TW202534429A - Method of pellicle detection, and computer program for pellicle monitoring - Google Patents

Abstract

A method of pellicle monitoring using an alignment sensor of a lithographic apparatus, wherein: the alignment sensor is configured to sense alignment using a patterning device alignment mark and a stage alignment mark; and the pellicle intersects a light path between the alignment sensor and the patterning device; wherein the method comprises: using the alignment sensor, measuring a first detection intensity; using the alignment sensor, measuring a second detection intensity, being the intensity of light reflected from the patterning device; and comparing the first and second detection intensities.

Description

Method for detecting pellicle and computer program for pellicle monitoring

The present invention relates to a technology for detecting the presence/integrity or absence/rupture of a pellicle and/or monitoring the remaining life of the pellicle.

A lithography system is a machine designed to deposit a desired pattern onto a substrate. Lithography systems are used, for example, in the manufacture of integrated circuits (ICs). They project a pattern (often referred to as a "design layout" or "design") of a patterned device (e.g., a mask) onto a layer of radiation-sensitive material (resist) disposed on a substrate (e.g., a wafer).

As semiconductor manufacturing processes continue to advance, the size of circuit components has steadily decreased over the past few decades, while the number of functional elements, such as transistors, per device has steadily increased, following a trend commonly known as "Moore's Law." To keep pace with Moore's Law, the semiconductor industry is seeking technologies that can produce ever-smaller features. To project patterns onto substrates, lithography equipment uses electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features that can be patterned on the substrate. Typical wavelengths currently in use are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm.

A lithography apparatus may include an illumination system for providing a projected radiation beam and a support structure for supporting a patterning device. The patterning device may be configured to impart a pattern to the projected beam in its cross-section. The apparatus may also include a projection system for projecting the patterned beam onto a target portion of a substrate.

Contaminant particles can be generated during exposure. If these particles are allowed to reach the patterning device and deposit on it, they can project an image onto the substrate, thereby causing defects in the substrate. As feature sizes continue to shrink, preventing the formation of such defects becomes increasingly important. For this purpose, the patterning device is often covered with a pellicle, which is an optically transparent diaphragm. However, pellicles have a limited lifetime and can break after several exposure cycles. When a pellicle breaks, a large number of contaminant particles are generated. In this situation, it may be necessary to pause the lithography equipment as quickly as possible. To achieve this, it may be necessary to monitor the status of the pellicle.

Therefore, one object of the present invention is to provide pellicle detection and/or monitoring. Another object is to provide pellicle detection without affecting the production throughput of the lithography equipment. Another object is to monitor the remaining life of the pellicle.

According to the present invention, a method for performing pellicle monitoring using an alignment sensor of a lithography apparatus is disclosed, wherein: the lithography apparatus includes a patterning device stage for supporting a patterning device; the patterning device stage includes a stage alignment mark fixedly disposed thereon; the patterning device includes a patterning device alignment mark fixedly disposed thereon; the alignment sensor is configured to use the patterning device alignment mark and the The lithography apparatus is configured to position a pellicle so that the pellicle intersects a light path between the alignment sensor and the patterning device; wherein the method includes: using the alignment sensor to measure a first detection intensity; using the alignment sensor to measure a second detection intensity, the second detection intensity being the intensity of light reflected from the patterning device; and comparing the first detection intensity and the second detection intensity.

In this document, the terms "radiation" and "beam" are used to cover all types of electromagnetic radiation, including ultraviolet radiation (e.g., having a wavelength of 436, 405, 365, 248, 193, 157, 126 or 13.5 nm).

As used herein, the terms "reduction mask," "mask," or "patterning device" should be broadly interpreted to refer to a general patterning device that can be used to impart a patterned cross-section to an incident radiation beam, corresponding to the pattern to be produced in a target portion of a substrate. The term "light valve" may also be used in this context. In addition to classic masks (transmissive or reflective, binary, phase-shifting, hybrid, etc.), examples of other such patterning devices include programmable mirror arrays and programmable LCD arrays.

FIG1 schematically depicts a lithography apparatus LA. The lithography apparatus LA includes an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., EUV radiation or DUV radiation); a patterning device stage or mask support (e.g., a mask stage) MT configured to support a patterning device (e.g., a mask) MA and connected to a first positioner PM configured to accurately position the patterning device MA according to certain parameters; a substrate support (e.g., a substrate stage or substrate holder) WT configured to hold a substrate (e.g., a resist-coated wafer) W and connected to a second positioner PW configured to accurately position the substrate support WT according to certain parameters; and a projection system (e.g., a refractive projection lens system or a reflective optics system). PS is configured to project the pattern imparted to the radiation beam B by the patterning device MA onto a target portion C of the substrate W (e.g., comprising one or more dies).

In operation, the illumination system IL receives a radiation beam B from a radiation source SO, for example, via a beam delivery system BD. The illumination system IL may include various types of optical components for directing, shaping, and/or controlling the radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, and/or other types of optical components, or any combination thereof. The illuminator IL may be used to condition the radiation beam B so as to have a desired spatial and angular intensity distribution in its cross-section at the plane of the patterning device MA.

The term "projection system" PS as used herein should be interpreted broadly as covering various types of projection systems, including refractive, reflective, catadioptric, synthetic, magnetic, electromagnetic and/or electrostatic optical systems, or any combination thereof, as appropriate to the exposure radiation used and/or other factors such as the use of an immersion liquid or the use of a vacuum. Any use of the term "projection lens" herein should be considered synonymous with the more general term "projection system" PS.

The lithography apparatus LA may be of a type in which at least a portion of the substrate W may be covered by a liquid having a relatively high refractive index (e.g., water) in order to fill the space between the projection system PS and the substrate W, which is also known as immersion lithography. More information on immersion technology is given in US Pat. No. 6,952,253, which is incorporated herein by reference.

The lithography apparatus LA may also be of a type having two or more substrate supports WT (also referred to as a "dual-stage" apparatus). In such a "multi-stage" apparatus, the substrate supports WT can be used in parallel, and/or a substrate W on one of the substrate supports WT can be prepared for subsequent exposure while another substrate W on another substrate support WT is being used to expose a pattern.

In addition to the substrate support WT, the lithography apparatus LA may also include a measurement stage (not shown in FIG1 ). The measurement stage is configured to hold a sensor and/or a cleaning device. The sensor may be configured to measure properties of the projection system PS or properties of the radiation beam B. The measurement stage may hold a plurality of sensors. The cleaning device may be configured to clean parts of the lithography apparatus LA, such as a part of the projection system PS or a part of the system for providing an immersion liquid. The measurement stage may be movable under the projection system PS when the substrate support WT is away from the projection system PS.

In operation, a radiation beam B is incident on a patterning device (e.g., a mask) MA, which is held on a patterning device stage MT, and is patterned by a pattern (design layout) present on the patterning device MA. Having traversed the mask MA, the radiation beam B passes through a projection system PS, which focuses the beam onto a target portion C of a substrate W. With the aid of a second positioner and a position measurement system, the substrate support WT can be accurately moved, for example, so that different target portions C are positioned at focused and aligned positions in the path of the radiation beam B. Similarly, the first positioner and possibly another position sensor (not explicitly depicted in FIG. 1 ) can be used to accurately position the patterning device MA relative to the path of the radiation beam B. The patterning device MA and substrate W can be aligned using the patterning device alignment marks MAF and substrate alignment marks. Although substrate alignment marks occupy dedicated target portions, they can be located in the spaces between target portions. When substrate alignment marks are located between target portions, they are referred to as scribe line alignment marks.

In this specification, the Cartesian coordinate system is used. The Cartesian coordinate system has three axes, namely the x-axis, the y-axis and the z-axis. Each of the three axes is orthogonal to the other two axes. The rotation about the x-axis is called the Rx rotation. The rotation about the y-axis is called the Ry rotation. The rotation about the z-axis is called the Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in the vertical direction. The Cartesian coordinate system does not limit the present invention and is only used for illustration. In fact, another coordinate system, such as a cylindrical coordinate system, can be used to illustrate the present invention. The orientation of the Cartesian coordinate system can be different, for example, so that the z-axis has a component along the horizontal plane.

As mentioned above, the lithography apparatus LA can be used to expose portions of a substrate W in order to form a pattern in the substrate W. To improve the accuracy with which the desired pattern is transferred to the substrate W, properties such as the alignment of the patterning device MA and/or the patterning device stage MT can be measured. Such alignments can include relative alignments, including relative alignment between the patterning device MA and the patterning device stage MT, relative alignment between the patterning device MA and the substrate support WT, and/or relative alignment between the patterning device stage MT and the substrate support WT. These properties can be measured regularly (often before and/or also after exposure of each substrate W), or they can be measured less frequently, for example, as part of a calibration procedure.

Determining the relative alignment of the patterning device stage MT and the substrate support WT facilitates directing the patterned radiation beam onto desired portions of the substrate W. This may be particularly important when projecting patterned radiation onto a substrate W that includes portions already exposed to radiation in order to improve alignment of the patterned radiation with previously exposed areas.

The alignment measurements described above can be performed by illuminating, as needed, alignment marks MAF fixedly disposed on the patterning device MA and/or alignment marks MTF fixedly disposed on the patterning device stage MT. The images generated by these alignment marks can be captured by an optical system such as an alignment sensor WS.

The patterned device alignment mark MAF and the stage alignment mark MTF can each have a reflective geometric pattern. Different geometric patterns may be suitable for different orientations or alignment accuracies. Examples of suitable geometric patterns include solid squares or rectangles, pinhole features, diffraction gratings, and checkerboard patterns. Furthermore, more than one alignment mark may be provided on each of the patterned device MA and the patterned device stage MT. It should also be understood that marks for purposes other than alignment (such as marks used for aberration detection) may also be present.

As shown in FIG1 , the patterning device alignment mark MAF can form part of the patterning device MA. One or more of these alignment marks MAF can be provided on the patterning device MA for performing the lithographic exposure. The alignment mark MAF can be positioned outside a patterned area of the patterning device MA, which is illuminated with radiation during the lithographic exposure. As mentioned above, a plurality of alignment marks MAF, MTF can be provided on each of the patterning device MA and the patterning device stage MT. The alignment operation can utilize one, several or all of these alignment marks MAF, MTF. For example, each of the alignment marks MAF, MTF can include a dedicated hardware segment, sometimes referred to as a “fiducial”. In some implementations, the patterning device alignment mark MAF can be etched directly into the patterning device MA along the patterned region of the patterning device MA. For the purposes of this description, the fiducial is considered an example of an alignment mark.

As shown in FIG1 , the lithography apparatus LA can be an EUV lithography apparatus and, therefore, utilize a reflective patterning device MA. Therefore, the patterning device alignment marks MAF can be reflective. In other lithography techniques, the patterning device MA can be transmissive, and, therefore, the patterning device alignment marks MAF can also be transmissive. It should be understood that the present invention can be implemented using either reflective or transmissive alignment marks, depending on the lithography technique employed.

To measure the alignment of the patterning device MA and the patterning device stage MT, an alignment sensor WS (as schematically shown in FIG1 ) can be provided to measure the light B′ output from the projection system PS. The alignment sensor WS can, for example, be disposed on or attached to the substrate support WT, as shown in FIG1 . To perform the alignment procedure, the patterning device stage MT can be positioned so that a stage alignment mark MTF is illuminated by light B from the illumination system IL, and the alignment sensor WS measures the image of the stage alignment mark MTF. Separately, the patterning device stage MT can be positioned so that a patterning device alignment mark MAF is illuminated by light B from the illumination system IL, and the alignment sensor WS measures the image of the patterning device alignment mark MAF. The substrate support WT may be positioned so that radiation reflected from the alignment marks MAF, MTF is projected onto the alignment sensor WS by the projection system PS.

The position of alignment features in the radiation beam B can be measured by an alignment sensor WS positioned at the level of the substrate W (for example, arranged on or attached to the substrate support WT, as shown in Figure 1). The alignment sensor WS is operable to detect the position of the alignment features in radiation incident thereon. This allows the alignment of the substrate support WT relative to the stage alignment mark MTF and/or the patterning device alignment mark MAF to be determined. Knowing the relative alignment of the patterning device MA and/or the patterning device stage MT and/or the substrate support WT, the patterning device MA and the substrate support WT can be moved relative to each other so as to form a pattern at a desired position on the substrate W (using the patterned radiation beam B' reflected from the patterning device MA). A separate measurement procedure may be used to determine the position of the substrate W on the substrate support WT.

During the exposure cycle, various contaminant particles may be generated. These particles, if allowed to reach the patterning device MA and deposit on it, may contaminate the patterning device MA. This contamination may cause the pattern on the patterning device MA to be indirectly reproduced on the wafer W, thereby causing defects. Therefore, it is common for the operator of the lithography apparatus LA to use a pellicle MP to protect the patterning device MA. Typically, a pellicle is a diaphragm that is optically transmissive to the light beam B. As shown in FIG1 , the pellicle MP may be arranged directly in front of the patterning device MA. The pellicle MP may be separated from the patterning device MA by a distance. This prevents the image of any contaminants present on the pellicle MP from being reproduced on the substrate W. For example, the distance between the pellicle MP and the surface of the patterning device MA may be about 1 mm. The pellicle MP itself may have a thickness of tens of nanometers. Typically, the film MP is not 100% transmissive to light B. High lighting efficiency generally requires a high level of transmissivity. Typically, the transmissivity of the film MP can be in the range of 75% to 95%.

The pellicle MP generally has a limited lifespan and may break after a certain number of exposure cycles. When the pellicle MP breaks, the pellicle MP may shatter and generate a large number of contaminant particles, which may flow to different parts of the lithography apparatus LA. This may at best cause defects in the exposed substrate W, and at worst damage components of the lithography apparatus LA. Therefore, in the event that the pellicle MP breaks, it may be necessary to suspend the lithography apparatus LA as quickly as possible. The surfaces of the components within the lithography apparatus LA may need to be cleaned, and the components of the lithography apparatus LA may need to be repaired or replaced. Therefore, it may be necessary to detect whether the pellicle MP is present and intact or has broken, so that the lithography apparatus can be suspended as needed. Additionally or alternatively, it may be necessary to monitor the remaining lifespan of the pellicle MP so that the pellicle MP can be replaced before the risk of rupture becomes too high.

To detect pellicle MP, consideration has been given to providing sensors specifically designed for this purpose. However, in addition to taking up space within the lithography equipment LA, these sensors also require additional machine time for operation. Therefore, while using these sensors to detect pellicle MP is theoretically possible, this comes at the expense of reduced production throughput. Furthermore, adding additional hardware, such as dedicated sensors, increases the complexity of the lithography equipment LA, creating additional sources of failure and making maintenance more burdensome.

However, as the inventors of the present invention have discovered, it is not necessary to provide a dedicated sensor for detecting the presence of a pellicle MP. Instead, the inventors of the present invention have discovered that it is possible to use the alignment sensor WS described above to detect the presence of a pellicle MP and to perform an alignment operation. Furthermore, by using the alignment sensor WS, it is possible to determine the presence of a pellicle MP while performing an alignment operation. In other words, by means of the present invention, it is possible to provide the additional functionality of pellicle monitoring or detection without consuming machine time, so that the output of the lithography apparatus LA can be maintained. Furthermore, the additional functionality of pellicle monitoring or detection can be provided without requiring new hardware (e.g., a sensor).

As shown in Figure 1 , the pellicle MP can be positioned to cover the patterning device MA and the patterning device alignment mark MAF, but may leave the stage alignment mark MTF uncovered. Therefore, light B' from the patterning device alignment mark MAF will pass through the pellicle MP (if present) before reaching the alignment sensor WS, while light from the stage alignment mark MTF will not pass through the pellicle MP before reaching the alignment sensor WS (even if a pellicle is present). In other words, the pellicle MP can be positioned so that it intersects the optical path between the alignment sensor WS and the patterning device MA. More specifically, the pellicle MP can be positioned so that it intersects the optical path between the alignment sensor WS and the patterning device alignment mark MAF. Furthermore, the pellicle MP can be positioned so that the optical paths between the different alignment sensors WS and the stage alignment mark MTF intersect. Similarly, in embodiments where the patterning device MA is of a reflective type, the light beam B from the illumination system IL will pass through the pellicle MP (if present and intact) before reaching the patterning device alignment mark MAF, but will not pass through the pellicle MP before reaching the stage alignment mark MTF (even if the pellicle is present).

As the inventors discovered, the fact that pellicle MP (if present) covers the patterned device alignment mark MAF but not the stage alignment mark MTF enables the use of alignment sensor WS to provide the additional functionality of detecting the presence of pellicle MP. As shown in FIG2a , when patterned device stage MT is positioned so that patterned device alignment mark MAF is exposed to light B from illumination system IL, if pellicle MP is present and intact, light B′ from patterned device alignment mark MAF will pass through pellicle MP. In the case of a reflective patterned device MA (as shown in FIG2a ), light B from illumination system IL will also pass through pellicle MP before reaching patterned device alignment mark MAF. Therefore, if the patterned device MA is reflective, light B from the illumination system IL will pass through the membrane twice before reaching the alignment sensor WS. In either case, whether light B passes through the membrane MP once (in the case of a transmissive patterned device MA) or twice (in the case of a reflective patterned device MA), the reflected light B' will be slightly attenuated by the membrane MP. Therefore, as shown in Figure 2a, the intensity of light B' detected by the alignment sensor WS can be relatively low.

In contrast, as shown in Figure 2b, when the patterning device stage MT has been displaced to a position where the stage alignment mark MTF is exposed to light B from the illumination system IL, the light B reaches and leaves the stage alignment mark MTF without passing through the pellicle MP. Therefore, the intensity of the light B' detected by the alignment sensor WS can be relatively high.

If the pellicle is absent or ruptured, light B from the illumination system IL will reach and leave the patterning device alignment mark MAF without passing through any pellicle. Therefore, the intensity of light B' detected by the alignment sensor WS can be relatively high and can be comparable to the intensity of light B' from the stage alignment mark MTF.

In other words, if the pellicle MP is present and intact, the alignment sensor WS can be expected to measure a lower intensity of light B' from the patterned device alignment mark MAF (compared to the light B' reflected from the stage alignment mark MTF). If the pellicle MP is absent or broken, the alignment sensor WS can be expected to measure comparable intensities of light B' from the patterned device alignment mark MAF and from the stage alignment mark MTF.

Therefore, according to one embodiment of the present invention, a method for detecting pellicle MP includes: using an alignment sensor to measure a first detection intensity; using the alignment sensor to measure a second detection intensity, which is the intensity of light reflected from a patterned device; and comparing the first detection intensity with the second detection intensity. By comparing the first and second detection intensities, it is possible to detect whether the pellicle MP is present and intact, or absent or ruptured.

More specifically, the pellicle MP can be monitored using the stage alignment mark MTF and the patterned device alignment mark MAF. In this case, the first detection intensity The intensity of the light reflected from the stage alignment mark and the second detection intensity It can be the intensity of light reflected from the alignment mark of the self-patterning device.

To selectively expose the patterning device alignment mark MAF and the stage alignment mark MTF, the relative position between light beam B and patterning device stage MT can be adjusted. Specifically, when measuring a first detection intensity, the relative position can be adjusted so that at least a portion of light beam B is incident on the stage alignment mark MTF, and the reflection of this at least a portion is measured as the first detection intensity. When measuring a second detection intensity, the relative position can be adjusted so that at least a portion of light beam B is incident on the patterning device alignment mark MAF, and the reflection of this at least a portion is measured as the second detection intensity. If a pellicle is present, this portion of light beam B passes through the pellicle.

As with any real-life system, the first and second intensities can be affected by many different factors. Detailed mathematical models can be developed to estimate what the first and second detection intensities will be when a pellicle MP is present or absent. Below is a description of some of the factors that affect the first and second detection intensities and how these factors can be taken into account. Of course, the more these factors are considered, the better the reliability of pellicle monitoring or detection can be. However, it should be noted that many of these factors can be simplified or ignored, and pellicle monitoring or detection can still be successfully performed by comparing the first and second detection intensities. More or fewer of these factors can be considered, depending on the desired level of reliability. Furthermore, many of these factors can be reduced to or approximated as constants, provided that consecutive measurements are performed under the same conditions (e.g., using the same settings, at the same or similar locations, and at the same or similar times).

When the image of the alignment marks MAF, MTF is captured by the alignment sensor WS as discussed above, the intensity I measured by the alignment sensor WS can be determined by: the average source power I from the illumination system IL during the measurement period , sensor response ρ _sensor , specific illumination settings (e.g. pupil transmittance T _pupil and slit position dependency T _slit ), transmittance of the projection system PS , Transmittance of Dynamic Gas Lock Diaphragm (DGLm) and film transmittance , the optical properties of the alignment mark (including the size of the projected mark image ), reflectivity of reflector mark , Align the size of sensor WS , the reflectivity of the light absorber around the marked reflective part (assuming the alignment sensor WS is larger than the image), and finally the measurement uncertainty _δmeas (here, this includes sensor noise _δsensor and horizontal and vertical misalignment of the detector relative to the marker image). For simplicity, the alignment mark MAF and MTF may have a square shape, but it should be understood that alignment marks with other shapes may be used. Mathematically, the intensity measured by the alignment sensor WS can be modeled as: EQ1:

The intensity defined above is linearly related to the source power and is proportional to the transmittance values of the various components along the optical column (i.e., from the patterning device MA to the substrate W, including any intervening mirrors M0, M1, M3, M4 and other optical components). More importantly, the intensity depends on the transmittance of the surface film MP. , the pellicle reduces the measured intensity when present relative to its absence and causes a decrease. If the patterning device MA is of the reflective type (as in EUV lithography), the pellicle MP can cause an intensity decrease of ( ) is proportional to the intensity drop, since the light beam B passes through the membrane twice, i.e. before and after being reflected on the patterning device MA. It should be noted that the invention can also be implemented using a patterning device MA of the transmission type, in which case the membrane MP can make the intensity drop proportional to ( ) because the beam B passes through the membrane only once.

As mentioned above, not all parameters listed in EQ1 need to be modeled to successfully perform pellicle detection. For example, it can be assumed that the source intensity remains constant over time because the patterned device alignment mark MAF and stage alignment mark MTF can be measured quickly and continuously, and/or because the source intensity The spatial variation of can be considered negligible. However, in order to achieve improved reliability of pellicle detection, the source intensity can be compensated Changes.

For example, compensation can be achieved by measuring the intensity of the first source , which is the intensity of the beam when measuring the first intensity; measuring the intensity of the second source , which is the intensity of the beam when measuring the second intensity; the compensation factor is calculated as and before comparing the first detection intensity and the second detection intensity, by The second detection strength is adjusted by multiplying the compensation factor. Specifically, an independent source power sensor (not shown) can be used to measure the source strength when measuring the first source strength and the second source strength. For example, the source power sensor can be placed close to the patterned device MA.

Another way to simplify EQ1 is to assume that the light absorption portion of the alignment mark MAF, MTF does not contribute to the first detection intensity and the second detection intensity as measured by the alignment sensor WS. That is, we can assume that is negligible, making the The item was deleted. However, to achieve improved reliability, the contribution from the light-absorbing portion can be compensated. In particular, as the film transmittance increases and due to variations in the optical properties of patterned devices MA from different manufacturers, the contribution from the absorber can become non-negligible. Furthermore, recent developments in patterned device technology, such as low-n masks, foresee the use of absorbers with relatively high reflectivities of up to approximately 15%, compared to a maximum reflectivity of 0.5% for baseline components and 2% for conventional tantalum-multiplied masks. Therefore, it may be necessary to compensate for the absorber contribution.

For example, by measuring (which is the intensity of light reflected from the absorber portion of the stage alignment mark MTF) and measurement The absorber contribution is determined by shifting the patterning device stage MT so that the entire image measured by the alignment sensor WS is from the area of light-absorbing material adjacent to the respective alignment mark MTF, MAF (assuming the same optical properties as the absorber portion of the alignment mark itself). Because the entire image measured by the alignment sensor WS in this operation is from the absorber material, it is necessary to scale the intensity measurement by a geometric factor S , which represents the fraction of the area of the absorber portion of the alignment mark MTF, MAF relative to the total area of the alignment mark MTF, MAF, in order to obtain an estimate of the absorber contribution. When performing pellicle monitoring or detection, the estimated absorber contribution can be subtracted from the first and second intensities measured by the alignment sensor WS before comparing them. The absorber contribution does not need to be remeasured during each exposure cycle. Instead, it can be remeasured once within an exposure cycle batch to limit the amount of machine time required.

In other words, the pellicle monitoring or detection method may include: measuring , which is the intensity of light reflected from the absorber portion of the stage alignment mark MTF; measure , which is the intensity of the light reflected from the absorber portion of the patterned device aligned with the MAF mark; the geometric factor is obtained , which is the ratio of the area of the absorber portion of the stage alignment mark MTF to the total area of the stage alignment mark MTF; the geometric factor is obtained , which is the ratio of the area of the absorber portion of the patterned device alignment mark MAF to the total area of the patterned device alignment mark MAF; before comparing the first detection intensity and the second detection intensity, by subtracting To adjust the first detection strength , and by subtracting To adjust the second detection strength .

As mentioned above, pellicle monitoring or detection can be achieved by comparing the first detection intensity and the second detection intensity. In some embodiments, comparing the first detection intensity and the second detection intensity can include: calculating a detection intensity ratio PDR , which is the first detection intensity and the second detection intensity and comparing the detection intensity ratio to a detection threshold Th . The detection threshold Th may be a predetermined threshold. For example, the detection threshold may be provided as a user input. Alternatively, the detection threshold may be calculated based on the optical properties of the relevant components, which may be provided as user input. As mentioned above, many of the factors in EQ1 may be considered constants over a certain time scale (e.g., the duration of a batch of exposure cycles), subject to the constraint that the measurement settings are equal. Thus, when calculating the detection intensity ratio PDR , these constants are eliminated or can be assumed to be eliminated.

As mentioned above, the intensity drop caused by the presence of the pellicle MP can be related to the transmittance of the pellicle MP. Therefore, the detection threshold Th can be based on And set. The value of can be taken from the reference film. For example, The value of can be provided by the user or can be predetermined in other ways. The reference film can be a film that is known to have average optical properties across film batches.

The detection strength ratio PDR can be defined as , so that if the detection intensity ratio PDR exceeds the detection threshold value Th , it can be determined that the pellicle MP does not exist or is ruptured. It should be understood that the inverse of this definition of PDR can be used, so that if the ratio drops below the detection threshold value, it can be determined that the pellicle MP does not exist or is ruptured.

As mentioned above, if the patterning device MA is of the reflective type, the light beam B may pass through the membrane MP twice and thus be attenuated twice by the membrane MP. Therefore, a decrease in intensity of ( ). Therefore, the detection threshold Th can be set as The detection threshold can be selected to a value between 1 and 1. Furthermore, the amount of measurement uncertainty can be considered in the selection of the detection threshold to avoid or reduce false positives or negatives in pellicle detection. The selection of the detection threshold can also take into account variations in transmittance from one pellicle MP to another. Therefore, the selection of the detection threshold can be informed by the use of a reference pellicle MP, which can have optical properties that are averaged across a population of pellicle MPs.

However, it can happen that for the surface film MP at the edge of a group, the PDR is not significantly different from the selected detection threshold Th. As a result, fluctuations in measurement uncertainty can occasionally cause the PDR to exceed the detection threshold Th , leading to false crack detections and unnecessary system downtime. Similarly, the optical properties of the patterning device alignment mark MAF can also vary within the patterning device MA. For example, under certain manufacturers, the reflectivity can vary by as much as approximately 10%.

In order to reduce false break detection, a solution is to use relative PDR inspection. That is, in a plurality of exposure cycles where the detection intensity ratio PDR is measured and calculated, the detection method may include: calculating the detection intensity ratio in exposure cycle n + 1 Ratio of detection intensity to the previous exposure cycle n The difference between , then the pellicle is considered complete in exposure cycle n + 1, where is equal to or greater than A determination of an intact membrane overrides any determination of a membrane absence or rupture. Thus, false rupture detections can be reduced or prevented.

As mentioned above, the detection threshold Th can be set as and 1, and the detection strength measurement may have a certain degree of measurement uncertainty δ _meas . Therefore, the detection threshold Th can be set to ,in is equal to or greater than In other words, the detection threshold Th can be set to the midpoint (halfway) between the maximum possible PDR that the alignment sensor WS can measure when the pellicle MP is present and the minimum possible PDR that the alignment sensor WS can measure when the pellicle MP is not present. It should be noted that and The values of may be unrelated and may be different or equal. In some embodiments, and Both can be set to .

In some cases, the alignment marks MAF, MTF may have different manufacturing processes and may sometimes be damaged or contaminated, or the alignment marks MAF, MTF may have different marking geometries, etc. As a result, in such cases, the nominal signal for a bare (i.e. not covered by a pellicle MP) patterned device MA may not be 100%, and similarly, the nominal signal for a patterned device MA with a pellicle MP may not be 100%. , making it higher than A detection threshold value of may not result in perfectly reliable detection. As a further improvement, one can, for example, determine the PDR with respect to a reference patterning device MA, which may be naked and deliberately chosen as the average value of a population of patterning devices MA. The resulting intensity ratio value PDR _meas can be used to set the detection threshold value Th to This value corresponds to the PDR measured for a bare patterned device MA and the PDR measured for a patterned device MA with a given nominal transmittance. The mean of the corresponding PDRs obtained in the case of pellicle MP.

In addition to or as an alternative to detecting when a pellicle MP is likely to rupture (or not), it may be useful to provide some advance warning so that the pellicle MP can be replaced before the risk of rupture becomes too high. Specifically, it may be useful to be able to measure the remaining life of the pellicle MP. For example, it may be useful to predict the number of exposures remaining before rupture is likely.

Therefore, referring to FIG. 4 , the method may further include: measuring and recording a transmittance value of the film at each of a plurality of time points; recording an exposure count x of the film when measuring each of the plurality of transmittance values; and using the plurality of transmittance values and the plurality of exposure counts as input data to a prediction model that predicts when the transmittance value of the film reaches a replacement transmittance threshold. The remaining number of impressions before X.

The transmittance value of the pellicle MP can be any measure of the transmittance of the pellicle MP to the radiation beam B, which may include EUV radiation. For example, the transmittance T _pel can be used directly as the measured transmittance value of the pellicle MP at each point in time. Alternatively, it can be calculated as The detection intensity ratio PDR of T2 can be used as the measured transmittance value of the pellicle MP at each time point. Alternatively, it should be noted that the detection intensity ratio PDR can be roughly correlated with T2 , ^and the square root of PDR can be used as the measured transmittance value of the pellicle MP at each time point.

As mentioned above, it may be beneficial to replace the pellicle MP before the risk of rupture becomes too high. Therefore, a replacement transmittance threshold may be defined. . Replace the transmittance threshold This corresponds to the transmittance threshold of the recommended replacement film MP. Replacement transmittance threshold The replacement transmittance threshold may be a predefined threshold value set by the operator of the lithography apparatus LA. The replacement transmittance threshold value may be determined based on a trade-off between maximizing the useful life of the pellicle MP and the risk of cracking. The value of.

In the case of certain types of pellicle materials, the pellicle MP may become increasingly transmissive to the radiation beams B and B' as the number of exposures increases. This increase in transmittance can occur through various mechanisms. For example, the pellicle MP material may become thinner due to repeated exposure to the radiation beam B. That is, the radiation beam B may etch away certain material of the pellicle MP during each exposure. Alternatively or in addition, the material of the pellicle MP may become less dense due to repeated exposure to the radiation beam B, resulting in an increase in transmittance. The pellicle MP may become more transmissive due to exposure to the radiation beam B in the presence of hydrogen.

For example, the pellicle MP can be made of carbon nanotubes (CNTs). CNTs are an ideal material choice for the pellicle MP because they can withstand the high intensity of EVU radiation. The CNT pellicle MP can exhibit increasing transmittance with increasing exposure times. This can be attributed to etching by the radiation beam B, resulting in a decrease in thickness over time. Alternatively or additionally, the CNTs can shrink due to exposure to the radiation beam B, resulting in an increase in transmittance. Specifically, the wall thickness of the CNTs can be reduced. The CNTs can shrink without substantially affecting the thickness of the pellicle MP. In essence, the CNT surface film MP may have a porous structure and may become optically less dense due to repeated exposure to the radiation beam B.

In one configuration, the transmittance threshold is replaced Set to a value less than 100% to allow for a safety margin. For example, replace the transmittance threshold It can be set to a value less than the detection threshold value Th . This is particularly applicable to the surface film MP, whose transmittance increases with the number of times it is exposed to the radiation beam B. By setting the replacement transmittance threshold value In this way, the operator can be prompted to replace the pellicle MP before it ruptures or is presumed to have ruptured. Specifically, the operator can be aware of the remaining number of exposures X and schedule the replacement of the pellicle MP at an appropriate time. The operator may not necessarily wait until the remaining number of exposures X reaches zero before replacing the pellicle MP. For example, the operator may choose to replace the pellicle MP earlier to avoid interrupting the operation of the lithography apparatus LA during an exposure batch. Similarly, for the same reason, the operator may not necessarily replace the pellicle MP immediately when the remaining number of exposures X reaches zero.

By way of example only, a typical CNT film MP may have a transmittance of about 90% to 96%, usually greater than 95%, when new. For example, replacing the transmittance threshold It can be set to correspond to a transmittance of approximately 98% to 99%.

As mentioned above, the prediction model can take transmittance values and exposure counts as input data. However, the input data can include additional parameters. That is, the input data space can have more than two dimensions (not shown in Figure 4). For example, the input data can include three, four, or even more parameters. Taking more input parameters into account can improve the accuracy of the prediction of the remaining number of exposures X.

For example, some operating schemes may involve varying the hydrogen pressure from one exposure cycle to another. Thus, the method may further comprise measuring and recording the hydrogen pressure surrounding the pellicle MP while measuring each of the plurality of transmittance values, and the input data may further comprise a plurality of hydrogen pressure measurements. Hydrogen pressure may be a useful input parameter because it may have an impact on the corrosion rate of the pellicle MP. Generally, higher hydrogen pressures are expected to result in higher corrosion rates. The hydrogen pressure may be considered to be equivalent to the main chamber pressure of the lithography apparatus LA. Alternatively, a dedicated pressure sensor may be provided in the environment surrounding the pellicle MP to measure the hydrogen pressure.

Similarly, some operating protocols may involve varying the temperature of the pellicle MP or the temperature of the environment surrounding the pellicle MP from one exposure cycle to another. Therefore, the method may further include measuring and recording the temperature of the pellicle MP or the temperature of the environment surrounding the pellicle MP while measuring each of the plurality of transmittance values, and the input data may further include a plurality of temperature measurements. Temperature can also be a useful input parameter because it may affect the corrosion rate of the pellicle MP. Generally speaking, higher temperatures are expected to result in lower corrosion rates.

Referring again to FIG4 , regardless of the number of input parameters, the prediction model can predict the remaining number of exposures X by performing a regression analysis on the input data and extrapolating from it. That is, the regression analysis can extrapolate the input data to predict that the transmittance value at the surface film MP will be equal to the replacement threshold value The cumulative exposure count at time , and the remaining exposure count X can be calculated as the difference between the predicted cumulative exposure count and the current exposure count (ie, the number of times the surface film MP has been exposed to the radiation beam B).

Without being bound by any particular theory, it has been observed that the relationship between exposure times and the transmittance of the pellicle MP can be roughly linear or slightly accelerated (hence, Figure 4 shows an upward-curving extrapolated line, but the degree of acceleration is exaggerated for illustrative purposes). This is particularly true for CNT pellicle MPs. Therefore, regression analysis can include linear regression. Linear regression provides a sufficiently accurate fit to the input data. To better account for acceleration effects, quadratic and/or exponential regression can be used.

Regression analysis, including linear, quadratic, and/or exponential regression, can also be used when the input data includes more than two parameters (i.e., exposure count x and transmittance value of the pellicle MP) (such as hydrogen pressure and/or temperature as mentioned above). However, as the dimensionality of the input data increases, and due to the potential nonlinear effects of the various input parameters, machine learning can be more effective in predicting the remaining exposure count X. Therefore, the prediction model can include training a machine learning model. Of course, it should be noted that machine learning can be used even when the input parameters only include exposure count x and transmittance value of the pellicle MP.

Because the pellicle MP is expected to gradually degrade, its transmittance can also be expected to gradually increase. However, as with any real-world measurement, the input data may contain unexpected fluctuations, such as measurement noise. Therefore, a noise filter may be applied to the input data. Specifically, the noise filter may be applied to the input data before applying the prediction model. For example, the noise filter may include a low-pass filter.

During the operation of the lithography apparatus LA, the following situation may occur: for example, due to contamination, the reference intensity provided by the stage alignment mark MTF may drift over time, thereby making the threshold value Th determined above invalid over time. This can be solved by the following operation: at the initial time point t ₀ , measure the reference first detection intensity (which is a first detection intensity that can be measured when the reference stage alignment mark is installed in the lithography apparatus) and measuring the first detection intensity At the subsequent time point t ₁ , the reference first detection intensity is re-measured , and remeasure the first detection intensity ; Set the drift factor Calculated as and at a subsequent time point t ₁ , before comparing the detection intensity ratio PDR with the detection threshold Th , by multiplying the detection intensity ratio by the drift factor To adjust the detection intensity ratio. The reference first detection intensity can be repeated from time to time. and first detection intensity The drift factor can be updated accordingly It should also be noted that In the definition of , common-mode effects (e.g., transmission of the optical rod) can be eliminated by dividing the intensity measurement at time t ₁ by the intensity measurement at time t ₀ .

Like the stage alignment mark MTF, the optical properties of the patterned device alignment mark MAF may also drift over time, for example due to contamination. Therefore, a second drift factor may be calculated and applied to account for this drift. For example, the pellicle detection method may include: at an initial time point t ₂ , measuring a reference first detection intensity (which is a first detection intensity that can be measured when the reference stage alignment mark is installed in the lithography apparatus) and a second detection intensity is measured Then, at a subsequent time point t ₃ (which may be after multiple exposure cycles), the film detection method may include: re-measuring the reference first detection intensity And re-measure the second detection intensity ; Set the second drift factor Calculated as and at a subsequent time point t ₃ , before comparing the detection intensity ratio PDR with the detection threshold Th , by multiplying the detection intensity ratio by a second drift factor to adjust the detection strength ratio.

It should be understood that in the second drift factor _The initial time point t2 mentioned in the context of The initial time point t0 mentioned in the context of _t0 has any time relationship. For example, _the initial time point t2 may coincide with the initial time point t0 _. Similarly, in the second drift factor _The subsequent time point t3 mentioned in the context of The subsequent time point t1 mentioned in the context of _may have any time relationship. For example, _the subsequent time point t3 may coincide with the subsequent time point t1 _.

In some embodiments, the pellicle MP and patterning device MA can be fixed together to form an assembly and can be installed and uninstalled together. In addition, in some embodiments, the pellicle MP and patterning device MA can be installed in the lithography apparatus LA for multiple exposure cycles, then swapped out for a different pellicle and patterning device for multiple exposure cycles, and then reinstalled for another exposure cycle. In some cases, the swap out and reinstallation can be separated by several months. When the pellicle MP and patterning device MA are reinstalled, the second drift factor can be used again. More generally, a second drift factor can be stored for each pair of pellicle MP and patterning device MA before the pair is swapped out. The last known value of the second drift factor can be retrieved when swapping back to the pair. A database can be created to store the second drift factor for each of the sets of pellicle MP and patterning device MA pairs. The known value of .

Specifically, the pellicle detection method may include: at time point t3 _, making the second drift factor Associated with the patterning device MA and the pellicle MP installed in the lithography equipment, and storing the second drift factor ; disassembling the patterning device MA and the membrane MP; and at a subsequent time point t ₄ after time point t ₃ , reinstalling the patterning device MA and the membrane MP and extracting a second drift factor associated with the patterning device and the membrane . In capturing the second drift factor Thereafter, for the exposure cycles starting from this point, the detection intensity ratio PDR can be multiplied by the acquired second drift factor before comparing it with the detection threshold Th. to adjust the detection strength ratio.

By reusing the second drift factor The last known value of can be used to appropriately compensate the strength detection ratio PDR before comparing it with the detection threshold Th , so that the likelihood of false detection can be reduced. When reinstalling the patterning device MA and pellicle MP pair, it may be necessary to allow for a large degree of uncertainty in the optical properties of the patterning device MA and pellicle MP pair. By reusing the second drift factor The last known value of can reduce or eliminate this uncertainty. Of course, as in any practical system, some uncertainty may remain. For example, the measurement uncertainty δ _meas mentioned above can be maintained.

Alternatively, PDR _{t3 can} be stored at time t3 . At time t4 , when calculating _{PDR t4} , PDR _{t3 and PDR t4} can be used to perform _the relative PDR check described above. That is, the relative PDR check can be performed starting from _the first exposure cycle after reinstallation, as if the patterning device MA and pellicle MP pair had never been removed and reinstalled. This can result in improved accuracy.

Like the alignment mark MAF and MTF, the entire lithography apparatus LA may also drift over time due to a number of contributing factors, including but not limited to degradation of the projection system PS and the illumination system IL, or any of the intervention mirrors M0, M1, M3 and M4. As shown in EQ1, the intensity measured by the alignment sensor WS is partially affected by the source power intensity P0 _. The system drift of _the entire lithography apparatus LA can be tracked by calculating the system transmittance factor. For example, the pellicle detection method may further include: at an initial time point t5 , measuring (which is the intensity _of the light beam at time t5 ) and (which is the _second detection intensity at time point t5 ); the system transmittance factor _at time point t5 Calculated as At the subsequent time point t ₆ , measure (which is the intensity _of the light beam at time t6 ) and (which is the second detection intensity at time point t ₆ ); the system transmittance factor at time point t ₆ Calculated as and before comparing the first detection intensity and the second detection intensity after the subsequent time point t6 , _by Multiply to adjust the second detection strength.

In addition, it should be understood that _the initial time point t5 mentioned here can be the same as the first drift factor and the second drift factor The initial time points t0 and t2 mentioned in the context of FIG have any time relationship. For example, _the initial time point t5 may coincide with the initial time point t0 _and /or _the initial time point t2 _. Similarly, the subsequent time point t6 mentioned here may _coincide with the initial time point _t6 mentioned above in the first drift factor. and the second drift factor _The subsequent time points t1 and t3 mentioned in the context of may have any time relationship. For example, _the subsequent time point t6 may coincide with _the subsequent time point t1 and/or _the subsequent time _point t3 .

In some embodiments of the lithography apparatus LA, there may be more than one substrate support WT, so that the next substrate W can be loaded while the current substrate W is being exposed. In addition, each substrate support WT can be associated with its own alignment sensor WS or equipped with an alignment sensor WS. For example, the lithography apparatus LA can include alternating substrate supports WT. That is, the lithography apparatus LA can include a first and a second substrate support WT. In addition to the first alignment sensor WS, the lithography apparatus LA can also include a second alignment sensor WS. The first alignment sensor WS can be associated with the first substrate support WT, and the second alignment sensor WS can be associated with the second substrate support WT.

Therefore, every other exposure step may be practically blind to the presence of a pellicle. Furthermore, as the alignment operation of the patterning device MA becomes more and more time-aggressive in order to increase the machine throughput, it may happen that the alignment sensor WS used for the alignment operation may be different each time, e.g. different sensors on the same substrate support WT or sensors from different substrate supports WT. Therefore, it may be necessary to compensate for the differences between different alignment sensors WS. For example, the pellicle detection method may further comprise: obtaining a sensitivity ratio , which is the sensitivity of the first alignment sensor Sensitivity of the second alignment sensor The ratio between the two is measured using a second alignment sensor. , which is the intensity of light reflected from the alignment mark of the patterning device; and sensitivity ratio Multiply to adjust ; and comparison and .

A priori calibration can be used to obtain sensitivity ratios However, this may require a specific measurement scheme and additional machine time to perform the calibration. Furthermore, sensor responsiveness may change over time, for example due to sensor contamination or aging, such that the initial a priori calibration may become inaccurate and recalibration may become necessary.

However, in an exposure sequence, there are naturally measurements performed under practically identical conditions. For example, consecutive alignment operations can be performed sequentially by the first and second alignment sensors WS using the same patterned device alignment mark MAF. The sensitivity ratio for each exposure batch can be easily calculated. , and the sensitivity ratio can be updated over time. In other words, if the exposure cycle m is measured , then it can be measured in exposure cycle m + 1 immediately following exposure cycle m , and the sensitivity ratio Can be set to .

However, this assumes that the pellicle MP is intact in both exposure cycles m and m + 1, an assumption that may occasionally fail. If the pellicle MP breaks between cycles m and m + 1, the calculated sensitivity ratio May not be correct. To improve the sensitivity ratio To enhance the robustness of the setup, when the lithography apparatus LA switches back to using the first alignment sensor WS (and the first substrate support WT) and detects that the pellicle MP is still intact, the calculation of the sensitivity ratio can be delayed until exposure cycle m +2 . That is, if the pellicle MP is intact in cycle m+2, then it must also be intact in cycle m +1. Furthermore, it is possible to confirm that the pellicle MP is intact in cycle m +2 because the measurements in cycles m and m +1 are both performed by the first alignment sensor WS. In other words, the pellicle detection method may further include: using the first alignment sensor WS to detect the pellicle MP in exposure cycle m + 2 following exposure cycle m + 1 , wherein the sensitivity ratio is set to Set to (Use the values measured in cycles m and m + 1). Sensitivity ratio Can be stored in cache memory for use in subsequent exposure cycles. In addition, by storing the sensitivity ratio , statistical averaging techniques can be applied to improve detection accuracy.

Of course, this approach also applies when measurements are not performed in two consecutive exposure cycles (with the constraint that the pellicle MP has not yet broken). More generally, it applies to any combination of sensors: different sensors in the same substrate support WT, sensors from different substrate supports WT, different pairs of alignment sensors WS and patterning device alignment marks MAF, and even different types of sensors.

Finally, it is worth noting that, assuming all other measurement conditions are equal, the sensitivity ratio depends only on the sensor response and not on the specific conditions and lighting settings of a particular exposure batch. Therefore, any measured sensitivity ratio It can be reused in subsequent batches, enabling earlier detection of membrane failures. In addition, the measured sensitivity ratios can be stored in a database, enabling statistical averaging methods to improve accuracy.

Similar to the concept of sensor sensitivity ratio described above, when there are multiple patterned device alignment marks MAF on the patterned device MA, the difference in the intensity of light reflected by the patterned device alignment marks MAF can also be compensated. Specifically, the pellicle detection method can further include: obtaining an alignment mark intensity ratio I _markA /I _markB , where I _markA is the intensity of reflected light that can be measured from a first patterned device alignment mark and I _markB is the intensity of reflected light that can be measured from a second patterned device alignment mark under equal conditions; using an alignment sensor to measure I _ret,markB , which is the intensity of light reflected from the second patterned device alignment mark; and before comparing the first detection intensity and the second detection intensity, is replaced by the second detection intensity. This can be beneficial because different patterning device alignment marks MAF can be used at different steps in an alignment operation, and different alignment operations can also use different patterning device alignment marks MAF. This method can be particularly effective if the patterning device alignment marks MAF are positioned closely together on the patterning device MA so that T _slit (see EQ1) is approximately constant.

It should be understood that the various adjustments and compensations described above can be freely combined as desired. In addition, each of the contributing factors identified in EQ1 that were not explicitly considered in the above disclosure can also be measured and calibrated. The multiplicative nature of these factors means that any such additional improvements can be included by multiplying the PDR by an additional compensation factor, if desired.

As mentioned above, the advantage of using the alignment sensor WS and alignment marks MAF and MTF to detect pellicle MP is that it requires little to no additional machine time, as all required raw measurements can already be acquired as part of conventional alignment operations. Therefore, the steps of measuring the second detection intensity and comparing the first and second detection intensities can be repeated during each exposure cycle. Furthermore, the lithography apparatus LA can be paused upon detecting the absence or rupture of the pellicle.

In addition to detecting pellicles MP, the method can also be extended to detect other optically transmissive membranes along the optical column between the patterning device MA and the alignment sensor WS. For example, the method can also be extended to detect dynamic gas lock membranes (DGLm). As is known in EUV lithography, DGLm can be used to prevent substrate contamination and/or debris from entering the projection system PS of the lithography apparatus LA.

In the context of the present invention, when the pellicle MP covers the patterned device MA but does not cover the patterned device MAF, DGLm (if present) always intersects the light path to the alignment sensor WS. Therefore, the light beam B' reaching the alignment sensor WS will be attenuated ( ) times, is the transmittance of DGLm (see EQ1). Specifically, both the first detection intensity and the second detection intensity will include attenuation. Therefore, the state of DGLm cannot be detected by comparing the first detection intensity and the second detection intensity. However, in the case of DGLm rupture, a jump in the first detection intensity and/or the second detection intensity can be expected ( ) times. Therefore, the film detection method can further include: obtaining the transmittance of DGLm ; When the first detection intensity and/or the second detection intensity in an exposure cycle is detected to be increased compared with the previous exposure cycle ( ) times, it is determined that the DGLm has been broken. In addition, in the case where the DGLm is broken between the measurement of the first detection intensity and the second detection intensity, it is expected that the intensity detection ratio PDR jumps ( ) times. This can also be used to detect DGLm cracks. The transmittance of the DGLm can be measured during a calibration step (e.g. at the beginning of an exposure batch) .

Various types of alignment sensors WS can be used to perform the present method. For example, the alignment sensor WS can include a transmissive image sensor (TIS). For example, detailed disclosures of TIS can be found in US 6888151 B2, WO 2022207259 A1, and WO 2017207512 A2, all of which are incorporated herein by reference.

Additionally or alternatively, the alignment sensor WS may comprise a Shearing Interferometer Phase Stepping Measurement Sensor (PARIS). Details of PARIS can be found in WO 2021069147 A1, WO 2022248154 A1, and WO 2022268679 A1, all of which are incorporated herein by reference. Furthermore, each of the stage alignment mark MTF and the patterned device alignment mark MAF may comprise an orthogonal grating for use with PARIS.

For each alignment mark MAF, MTF, PARIS can first orient one grating (e.g., U grating) and then perform phase stepping measurements on another orthogonal grating (e.g., V grating). This generates two wavefront data, so that for each pixel in the sensor, the measured intensity I can be described as .

is the offset component, which is linearly proportional to the incident light on the sensor and is therefore proportional to: the source power , Grating reflectivity of the grating structure of the patterned device alignment mark MAF and absorber reflectivity and/or grating reflectivity of the stage alignment mark MTF The average value of the surface transmittance T _pel ² of the surface film MP and the transmittance of the projection system PS 、PARIS sensitivity etc. Therefore, the DC component can be modeled as: In the typical case of a binary mask grating (negligible absorber reflectivity), it becomes:

is the magnitude of the phase modulation component of the signal, which has similar dependencies on the source power, the projector box PS transmittance, the PARIS sensitivity, etc., and in terms of the grating surface properties, it is the contrast between the grating reflectivity and the background absorber. Therefore, M can be modeled as: In the typical case of a binary mask raster, this becomes:

finally, A phase that describes the aberration state of a lens and is not relevant to pellicle detection.

As can be seen, DC and M are equally sensitive to the presence of the membrane due to their common dependence on various parameters. On the other hand, their sensitivities to measurement disturbances differ (for example, the modulated component is also sensitive to aberrations perceived by the sensor; for example, defocus blurs the image and reduces the modulation, while offset does not). Therefore, the redundancy provided by these two measurements provides further robustness against systematic errors compared to a single measurement.

Each of DC and M can be used to detect the transmittance change caused by the rupture of the surface film MP. That is, the first detection intensity can be derived from the offset component DC of the same pixel or pixel group. and the second detection intensity Alternatively or additionally, the phase modulation components of the same pixel or pixel group may be Derivation of the first detection intensity and the second detection intensity Specifically, the first detection intensity can be derived from the magnitude M of the phase modulation component of the same pixel or pixel group. and the second detection intensity Each of them.

In addition, in order to improve the statistical confidence, the first detection strength can be derived from both the offset component DC and the magnitude M of the phase modulation component of the same pixel or pixel group. and the second detection intensity For example, the first detection intensity can be derived from a linear combination of the offset component DC and the magnitude M of the phase modulation component of the same pixel or pixel group. and the second detection intensity More specifically, the first detection intensity and the second detection intensity Each of them can be calculated as the average value of the magnitude M of the offset component DC and the phase modulation component of the same pixel or pixel group.

The detection intensity ratio PDR can be calculated as discussed above: As can be seen, except for the absence/rupture of the pellicle MP, All terms except 、 、 and Eliminated in PDR. In addition, when using PARIS, all adjustments and compensations disclosed above can also be applied.

In addition, as the inventors of this case have discovered, the ratio (in: and , and are the values of the offset component and the phase modulation component of the pixel or pixel group that can be measured from the stage alignment mark MTF, and and The magnitude of the offset component and the phase modulation component of a pixel or group of pixels, respectively, generated by light reflected from the patterning device alignment mark MAF, may be constant regardless of the presence/integrity of the pellicle MP.

Therefore, the pellicle detection method can further include: using PARIS to measure 、 、 and ; Calculation and monitoring The value of; and when detected After it has changed by more than a predetermined amount, the measurement is deemed unreliable. This may indicate instability in the system, incorrect measurement or error, and any obvious detection of a membrane rupture may be ignored.

As mentioned above, PARIS outputs an array of pixels. The above mathematical description of the output of PARIS applies to individual pixels. Therefore, all of the above techniques can be performed based on a single pixel only. However, in order to achieve improved statistical confidence and measurement uncertainty suppression, the above techniques can be performed by averaging groups of pixels. Specifically, the pixel group can be selected from a subset of pixels with the best performance. For example, the pixels located in the center of the PARIS field of view can be selected because these pixels generally produce a stronger signal and therefore have a better signal-to-noise ratio. Alternatively, the pixel group can be selected from a pixel group that is less sensitive to noise sources.

Furthermore, in an embodiment of PARIS, also referred to as parallel ILIAS, multiple pairs (e.g., seven pairs) of U and V detectors can be used simultaneously. In this embodiment, PARIS can measure a corresponding plurality (e.g., seven) of alignment marks MAF fixedly disposed on the patterned device MA. Furthermore, the patterned device alignment marks MAF can be distributed over the full width of the light B'. Thus, PARIS can generate a set of wavefront data for each of the U and V detectors in each of the multiple detector pairs, and each set of wavefront data can be decomposed into DC and M terms. For PARIS with seven pairs of U and V detectors, 2 x 2 x 7 = 28 simultaneous measurements of the pellicle can be generated at once. These simultaneous measurements can be used collectively for correlation analysis and statistically robust detection. Specifically, the first detection strength may be derived from the average of the outputs from a plurality of detectors. and the second detection intensity For each of these, these outputs may be generated simultaneously.

Using PARIS for pellicle detection offers another performance advantage over TIS. TIS's performance for pellicle detection can be limited by the residual reflectivity of the absorber portion of the alignment mark's MAF and MTF, as well as sensor manufacturing tolerances. This can introduce systematic errors in the measured intensity ratio (PDR ) of up to 15% to 20%. When using TIS for pellicle detection, accuracy can be improved by performing additional measurements, but this comes at the expense of machine time and, therefore, throughput.

In the case of PARIS, in the case of a non-binary (i.e., with high absorber reflectivity, e.g., up to 13%) patterned device alignment mark MAF, assuming the geometric design is still binary, the DC and M ratios can be modeled as: and

Averaging the above two terms, we get: , which is independent of the absorber reflectivity. This makes the contribution of the absorber reticle-to-reticle error to the detection accuracy practically negligible.

Therefore, to take advantage of this, the pellicle monitoring method may further comprise: using PARIS to measure and , which are the magnitudes of the offset component and phase modulation component of a pixel or pixel group generated by the light reflected from the stage alignment mark; measured using PARIS and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group generated by the light reflected from the alignment mark of the patterning device; the detection intensity ratio PDR is calculated as ,in and .

In the case of certain membrane materials, including but not limited to CNT membranes, the membrane MP can degrade gradually rather than completely. For example, the membrane MP may initially tear locally, and the failure area may expand over time, folding and wrapping around until the entire membrane MP fails. It may be necessary to detect failures early in the process, before the membrane MP completely fails.

However, using the second intensity It may be difficult to detect the early stages of failure of the pellicle MP by local measurements. That is, unless the second intensity The measurement point coincides with the fault point of the membrane MP, otherwise it may not be possible to detect the early stage of the fault.

One proposal is to monitor the entire surface of the pellicle MP at many sample points. However, such a procedure would require a considerable amount of measuring time. Furthermore, the patterning device MA would have to be equipped with a large number of measurement marks (one for each sample point), which would take up a considerable amount of surface area that could otherwise be used for exposing features. In particular, if the entire surface of the pellicle MP were to be checked before each exposure of the substrate W, each exposure cycle could be extended by a corresponding amount, which could significantly reduce the throughput of the lithography apparatus LA. In some scenarios, even sampling the entire surface of the pellicle MP once per exposure batch could result in an unacceptable reduction in the throughput of the lithography apparatus LA. For reference, in one proposed measurement scheme, sampling the entire surface of the pellicle MP requires approximately 30 to 60 seconds.

Therefore, it may be necessary to monitor the entire surface of the pellicle MP without losing too much throughput of the lithography apparatus LA.

As mentioned above, the output of PARIS provides two wavefront data, so that for each of the pixels in the sensor, the measured intensity I can be described as As discovered by the inventors of this case, although the phase term The transmittance of the surface film is not sensitive, but it carries information about the wavefront on the PARIS pixel array, from which aberrations in the optical system can be deduced.

However, it is worth noting that when the pellicle MP is mounted on the patterned device MA, even if the pellicle has a high transmittance , their presence can still contribute to the overall aberration content that can be measured by PARIS. In particular, local inhomogeneities, defects, transmittance variations, etc. in the surface film material can be expected to affect higher-order aberrations.

Therefore, as pellicle MP gradually wears and cracks develop in its diaphragm structure, while still mounted above patterning device MA, its mechanical structure can undergo significant changes. This can lead to different mechanical equilibriums, different asymmetric tensions and diaphragm stresses, wrinkles, and so on, each of which can modify the state of pellicle MP from its original intact state. In other words, localized damage can produce globally observable changes to pellicle MP. These changes, in turn, can alter the aberrations measurable by PARIS. More specifically, these changes can impart different "fingerprints" to the terms of the Zernike polynomials that can be extracted from the PARIS measurements.

Thus, as discovered by the present inventors, the output of PARIS can enable early detection of pellicle MP failures. Specifically, Zernike aberration terms that can be derived from the output of PARIS can be used. Furthermore, while PARIS can perform local measurements of the pellicle MP, the global state of the pellicle MP can be inferred from the output of PARIS. Thus, by using the output of PARIS, it may not be necessary to sample the entire surface of the pellicle MP. Furthermore, it is possible to extract Zernike aberration terms from PARIS measurements already performed during alignment of the patterning device MA, making it possible to eliminate the need for additional measurements and adding no time penalty to the exposure cycle.

Specifically, when using PARIS, the first detection intensity and the second detection intensity Each of may be a field corresponding to an intensity value of a pixel array output by PARIS. Thus, the method may comprise determining the presence of and/or For example, the method may include determining the existence of one or more non-zero order terms in the Zernike polynomials for the aberration in and/or At least one Zernike term of the second or third order (the second and third orders are rotated 90° relative to each other but otherwise have the same angular and radial frequencies) or higher in the aberrations of the image. The order of the Zernike terms is defined according to the Noll ordering scheme (Noll, RJ (1976). "Zernike polynomials and atmospheric turbulence". J. Opt. Soc. Am. 66 (3): 207. Bibcode:1976JOSA...66..207N. doi:10.1364/JOSA.66.000207.). Several Zernike terms of the second, third, or higher order may be determined. For example, at least one Zenkal term of order 5 or 6 or higher can be calculated.

While degradation of the pellicle MP may manifest itself in all Zenith terms, different order Zenith terms may be more or less affected by different factors. For example, low-order Zenith terms (e.g., up to order 4) may be more affected by translational alignment errors (e.g., caused by other parts of the lithography apparatus LA, particularly the patterning device stage MT), while higher-order Zenith terms may be more indicative of degradation of the pellicle MP. For example, for purposes of this invention, "higher order" Zenkal terms may include order 5 or 6 and higher, or order 7 or 8 and higher, or order 9 or 10 and higher, or order 11 and higher, or order 12 or 13 and higher, or order 14 or 15 and higher.

The method may further comprise comparing the Zernike aberration in the second detection intensity of the current exposure and the Zernike aberration in the first detection intensity For example, the Zernike aberration in the second detection intensity measured from the patterning device alignment mark MAF of the current exposure can be Subtracting the Zernike aberration from the first detection intensity of the MTF measurement of the stage alignment mark As mentioned above, it is not necessary to measure the first detection intensity every time the substrate W is exposed. For example, in some scenarios, a first detection intensity may be measured per exposure batch. once. This comparison eliminates any aberration contributions from various components along the optical column (i.e., from the patterning device MA to the substrate W, including any intervening mirrors M0, M1, M3, M4, and other optical components), the alignment mark MAF and MTF, and the contribution from PARIS itself. Therefore, any remaining contributions can be assumed to be from the patterning device MA and the pellicle MP.

It should be understood that the Zernike aberration in the second detection intensity May be subject to additional or alternative formal procedures or inspections.

For example, as shown in FIG5a, the method may further include comparing the Zernike aberration in the second detection intensity of the current exposure The Zörnicke aberration in the second detected intensity of the first exposure within the same exposure batch is compared. This can be done, for example, within each exposure batch. This comparison makes it possible to eliminate any contribution from the patterning device MA.

For example, as shown in FIG5b, the method may further include comparing the Zernike aberration in the second detection intensity of the current exposure The Zöller aberration in the intensity of the second detected exposure is compared to the immediately preceding exposure. This comparison enables the detection of small changes from one exposure to the next and increases the detection frequency.

For example, as also shown in FIG5b, the method may further comprise comparing the Zörnicke aberration in the second detected intensity of the first exposure in the current exposure batch The Zörnicke aberration in the second detected intensity of the last exposure in the immediately preceding exposure batch can be compared. This comparison enables the detection of the aforementioned minor variations in the intensity of the first exposure in an exposure batch. This comparison can be particularly effective when the same patterning device MA and/or the same pellicle MP are used for both the current exposure batch and the previous exposure batch.

For example, as shown in FIG5c, the method may further include comparing the Zernike aberration in the second detected intensity of the current exposure in the current exposure batch and the Zernike aberration in the second detected intensity of the corresponding exposure in the immediately preceding exposure batch.

It should be understood that the above comparisons can be freely combined as needed.

It should also be understood that the above comparisons can be based on any one Zenkie term of order 2, 3, or higher. Furthermore, the above comparisons can be based on multiple Zenkie terms of order 2, 3, or higher. For example, the comparisons can be performed term-by-term. Additionally or alternatively, two or more of the Zenkie terms can be combined before comparison (e.g., by adding coefficients as a weighted sum).

Each of the above comparisons can be used to determine whether the pellicle MP is worn. For example, for each of the above comparisons, the method may include: if the difference of at least one Zehnke term of order 2, 3, or higher exceeds a predetermined threshold, indicating that the pellicle is worn.

It should be understood that any Zenkal aberration can also be used to monitor the pellicle MP using parallel ILIAS (as explained above). In the case of parallel ILIAS, since measurements are taken at multiple locations simultaneously, it is possible to construct an aberration map of the entire pellicle MP surface using the Zenkal terms extracted from each of the PARIS sensors in the parallel ILIAS terms. Furthermore, in the case of parallel ILIAS, additional metrics can be defined by observing the differences in measurements from different PARIS sensors (specifically, the PARIS sensors corresponding to the patterned device alignment marks MAF located at the extreme ends of the slits, or sensors located at any locations on the geometric nodes or pellicle MP region that are important for a particular Zenkal "fingerprint").

Furthermore, in addition to or as an alternative to monitoring the early stages of failure of the pellicle MP, the Zörnik aberration can be used to monitor the health of the pellicle MP or to estimate the remaining life of the pellicle MP (due to aging and degradation).

In addition to or as an alternative to using the stage alignment mark MTF and the patterned device alignment mark MAF, pellicle monitoring can be performed using light reflected from the patterned device MA. Specifically, pellicle monitoring can be performed using a detection intensity map of the patterned device MA. Specifically, measuring a first detection intensity can include measuring the intensity of light reflected from a plurality of locations of the patterned device MA, thereby generating a first detection map. Measuring a second detection intensity can be performed after measuring the first detection intensity and can include measuring the intensity of light reflected from a plurality of locations of the patterned device MA, thereby generating a second detection map. Comparing the first detection intensity and the second detection intensity can include comparing the first detection map and the second detection map.

The values of the first and second detection maps can be offset by attenuation caused by the patterning device MA itself. That is, the first and second detection maps can be offset from a reference detection map measured on a "bare" patterning device MA. In other words, the reference detection map can be measured without the pellicle MP intersecting the optical path between the alignment sensor and the patterning device MA.

Comparing the first and second detection maps may include calculating a difference map by subtracting the first and second detection maps from each other.

In embodiments where the first and second detection maps are offset from a reference detection map, it can be assumed that the values in the difference map are determined entirely or primarily by the local transmittance values of the pellicle MP at a plurality of locations. Furthermore, the values in the difference map can be normalized by the corresponding values in the reference detection map (obtained from the bare patterning device MA) so that the difference map can contain variations in the local transmittance values of the pellicle MP (e.g., in terms of percentage variations in the values in the first detection map, or as dimensionless numbers).

In embodiments where the first detection map is obtained in the presence of a pellicle MP, the values in the difference map may represent variations in detection intensity at a plurality of locations of the pellicle MP.

Various metrics can be determined from the first and second detection maps and can be used individually or in combination to determine the state of the pellicle MP.

For example, a mean difference can be calculated from the difference map. If the mean difference exceeds a predetermined mean difference threshold, it can be determined that the pellicle MP is absent or ruptured. The predetermined mean difference threshold can be determined in various ways. For example, the predetermined mean difference threshold can be determined experimentally. Alternatively, the predetermined mean difference threshold can be determined from historical data. For example, the predetermined mean difference threshold can be set to an envelope of transmittance values corresponding to a population of known intact pellicle MPs.

Figure 6a depicts a difference map for a pellicle MP determined to be intact. This difference map is generated by subtracting the first detection map from the second detection map. In this example, the first and second detection maps are each offset from a reference detection map obtained for a bare patterned device MA (i.e., without the pellicle MP present). Therefore, the first and second detection maps contain values obtained at two points in time, assumed to measure the contribution from the pellicle MP and assumed to exclude any attenuation caused by the patterned device MA. The values in the difference map are also normalized so that they are actually a measure of the change in local transmittance values at each location of the pellicle MP (i.e., a value of 0 corresponds to no transmittance change; a value of +1% corresponds to a 1 percentage point increase in transmittance). In Figure 6a, the vertical axis shows the transmittance change. Figure 6b is a histogram of the difference map of Figure 6a.

As can be seen visually in FIG6b, the mean difference is approximately 0% (dRT = 0.1%), which is below the predetermined mean difference threshold, which in this example is set to 2.0% (ie, a 2.0 percentage point increase in transmittance).

Figures 7a and 7b illustrate an example where the pellicle MP was determined to have ruptured. These plots were generated in the same manner as Figures 6a and 6b, except using data from a different scenario. Like Figures 6a and 6b, Figure 7a is a difference map showing the variation in local transmittance values, and Figure 7b is a histogram of the difference map in Figure 7a.

As can be seen from Figure 7b, the mean difference (dRT) was approximately 2.4%, which exceeded the predetermined mean difference threshold of 2.0%. Therefore, the pellicle MP was determined to have ruptured.

While the mean difference is a valid metric, there are situations where a ruptured pellicle MP cannot be detected based solely on the mean difference. For example, if the rupture of the pellicle MP is very localized, the contribution of the rupture to the mean difference may be relatively small, and the mean difference may not exceed a predetermined mean difference threshold. However, even if the rupture is localized, the pellicle MP may still require immediate replacement.

Therefore, other metrics may be used in addition or instead. In particular, metrics that measure the distribution of values in the detection map and/or the difference map may be used.

For example, a metric can be defined to measure how widely the values in the difference map are spread out. Specifically, the difference map can be converted into a histogram of the difference values. Based on the histogram of the difference values, the width of the distribution of the difference values can be calculated. Different definitions of the distribution width can be used. For example, the width can be defined as the width of the minimum difference range that covers a large proportion (e.g., 70%, 80%, 90%, 95% or 98%) of the data points. For another example, the distribution width can be the standard deviation of the difference map values. If the distribution width exceeds a predetermined distribution width threshold, it can be determined that the surface film is not present or is ruptured. The predetermined distribution width threshold can be determined experimentally or can be determined from historical data. For example, the predetermined distribution width threshold can be determined as a multiple of the standard deviation of the transmittance values of a known complete pellicle MP population.

Figures 8a and 8b illustrate the use of distribution width to detect ruptured pellicle MP. Figures 8a and 8b were generated in the same manner as Figures 6a, 6b, 7a, and 7b, except that data from a different scenario was used. Figure 8a shows the difference map for this example, and Figure 8b is a histogram of the difference map. In the example shown in Figures 8a and 8b, the pellicle MP was not judged ruptured based on the mean difference metric discussed above because the mean difference (dRT) was only 1.8%, which is below the 2.0% threshold. As can be seen visually in Figure 8a, the rupture is relatively localized, resulting in relatively small changes in the mean difference. However, the distribution width (defined here as the width of the minimum difference range covering 90% of the data points) is 6.8%, which is higher than the predetermined distribution width threshold, which is set to 4.0% (i.e., 4 percentage points for transmittance) in this example.

As mentioned above, the distribution width alone can be used to detect a ruptured membrane MP. Therefore, the example shown in Figures 7a and 7b would also result in a determination of a ruptured membrane MP, since the distribution width in the histogram of Figure 7b (defined in the same manner as in Figure 8b, as described above) is 7.6%, which exceeds the 4.0% threshold.

Alternatively, the distribution width metric can be used in conjunction with other metrics, such as the mean difference mentioned above. More specifically, the mean difference can be used as the primary metric, and the distribution width as the secondary metric. That is, the distribution width metric can be used only when the mean difference metric determines that the pellicle is not ruptured. More specifically, the step of determining that the pellicle is absent or ruptured if the distribution width exceeds a predetermined distribution width threshold can be performed only when the mean difference is determined to be within a predetermined mean difference threshold. For example, as mentioned above, although the scenarios in Figures 8a and 8b do not result in a determination of a ruptured pellicle MP based on the mean difference metric, a determination is made using the distribution width metric. In contrast, since the scenarios in Figures 7a and 7b result in the determination of a ruptured membrane MP based on the mean difference metric, there is no need to apply the distribution width metric.

As yet another metric that can be used alone or in combination with the mean difference metric and/or the distribution width metric, the condition of the pellicle MP can be determined based on the distribution pattern of the detection values. For example, the first detection map and the second detection map can be converted into a first histogram and a second histogram of the detection values, respectively. A first distribution pattern can then be determined from the first histogram of the detection values, and a second distribution pattern can be determined from the second histogram of the detection values. Generally, while the transmittance values of an intact pellicle MP will exhibit some dispersion, the pellicle MP tends to be homogeneous, and the transmittance values tend to exhibit a unimodal distribution. In contrast, a damaged or cracked pellicle MP may be less homogeneous, and the transmittance values tend to exhibit a multimodal distribution. In particular, a bimodal distribution in the transmittance values can be expected in cases where the pellicle MP has been disrupted in such a way that there are areas where the pellicle MP is absent and other areas where the pellicle MP is intact.

Therefore, if the first distribution mode is a unimodal distribution and the second distribution mode is a multimodal distribution (or more specifically, a bimodal distribution), it can be determined that the surface film has been ruptured.

Although Figures 6a, 7a, and 8a are difference maps rather than detection value maps, and Figures 6b, 7b, and 8b are histograms of the corresponding figures 6a, 7a, and 8a, the histograms of the detection values exhibit the same distribution pattern as the corresponding histograms of the difference values.

As can be seen in Figure 6b (for intact pellicle MP), the histogram shows a unimodal distribution. Therefore, based on the distribution pattern metric, the pellicle MP is judged to be unruptured.

In each of the examples in Figures 7b and 8b, the pellicle MP is determined to be ruptured based on the distribution pattern metric. In each of Figures 7b and 8b, the histograms exhibit a multimodal (specifically, bimodal) distribution. Comparing Figures 7b or 8b with Figure 6b shows that the distribution pattern has changed from unimodal to multimodal, and the pellicle MP is determined to be ruptured based on the distribution pattern metric. More generally, a shift away from a unimodal distribution (i.e., a shift from unimodal to multimodal) can indicate a rupture.

In addition to the pellicle detection method, a method of manufacturing a device is also disclosed, which includes the pellicle detection method disclosed above.

Also disclosed is a computer program comprising instructions for causing a lithography apparatus to execute the pellicle detection method disclosed above.

Also disclosed is a lithography apparatus configured to perform the above-disclosed method for pellicle detection.

Although specific reference may be made herein to the use of lithography equipment in IC manufacturing, it should be understood that the lithography equipment described herein may have other applications, such as in the fabrication of integrated optical systems, guide and detection patterns for magnetic resonance memory, flat panel displays, liquid crystal displays (LCDs), thin-film magnetic heads, and the like. Those skilled in the art will appreciate that any use of the terms "wafer" or "die" herein in the context of such alternative applications may be considered synonymous with the more general terms "substrate" or "target portion," respectively. The substrates referred to herein may be processed, before or after exposure, in, for example, a track (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology tool, and/or an inspection tool. Where applicable, the disclosure herein may be applied to these and other substrate processing tools. In addition, a substrate may be processed more than once, for example to produce a multi-layer IC, so that the term substrate as used herein may also refer to a substrate that already contains one or more processed layers.

Although specific reference may be made above to the use of embodiments of the present invention in the context of photolithography, it will be appreciated that the invention may be used in other applications.

Aspects of the present invention are described in the following numbered clauses. 1. The present invention provides a method for performing pellicle monitoring using an alignment sensor of a lithography apparatus, wherein: the lithography apparatus includes a patterning device stage for supporting a patterning device; the patterning device stage includes a stage alignment mark fixedly disposed thereon; the patterning device includes a patterning device alignment mark fixedly disposed thereon; the alignment sensor is configured to use the patterning device alignment mark and the patterning device alignment mark to monitor the pellicle surface; 2. The method of claim 1, wherein: the lithography apparatus is configured to position a pellicle so that the pellicle intersects an optical path between the alignment sensor and the patterning device; wherein the method comprises: using the alignment sensor to measure a first detection intensity; using the alignment sensor to measure a second detection intensity, the second detection intensity being the intensity of light reflected from the patterning device; and comparing the first detection intensity and the second detection intensity. is the intensity of the light reflected from the stage alignment mark; the second detection intensity is the intensity of light reflected from the patterning device alignment mark. 3. The method of clause 2, further comprising adjusting the relative position between a light beam and the patterning device stage so that: when measuring the first detection intensity, at least a portion of the light beam is incident on the stage alignment mark, and the reflection of the at least a portion is measured as the first detection intensity; and when measuring the second detection intensity, at least a portion of the light beam is incident on the patterning device alignment mark, and the reflection of the at least a portion is measured as the second detection intensity, and in the presence of the pellicle, the portion of the light beam passes through the pellicle. 4. The method of clause 3, further comprising: measuring a first source intensity , which is the intensity of the light beam when measuring the first intensity; measuring a second source intensity , which is the intensity of the light beam when measuring the second intensity; a compensation factor is calculated as and before comparing the first detection strength and the second detection strength, by 5. The method of clause 3 or clause 4, wherein each of the patterned device alignment mark and the stage alignment mark is defined by a geometric arrangement of a reflective portion and an absorber portion, and the method further comprises: measuring , which is the intensity of light reflected from the absorber portion of the stage alignment mark; measuring , which is the intensity of light reflected from the absorber portion of the patterned device alignment mark; obtain the geometric factor , which is the ratio of the area of the absorber portion of the stage alignment mark to the total area of the stage alignment mark; the geometric factor is obtained , which is the ratio of the area of the absorber portion of the patterned device alignment mark to the total area of the patterned device alignment mark; before comparing the first detection intensity and the second detection intensity, by subtracting To adjust the first detection strength , and by subtracting To adjust the second detection strength 6. The method of any one of clauses 2 to 5, wherein the comparing the first detection strength and the second detection strength comprises: calculating a detection strength ratio PDR , the detection strength ratio being the first detection strength With the second detection strength and comparing the detected intensity ratio with a detection threshold value Th . 7. The method of clause 6, wherein the detection threshold value Th is a predetermined threshold value. 8. The method of clause 6 or clause 7, further comprising: obtaining a transmittance of a reference film for the measured light. , and based on The detection threshold Th is set. 9. The method of clause 8, wherein the detection intensity ratio PDR is calculated as , and the method further comprises: if the detection intensity ratio PDR exceeds the detection threshold value Th , then determining that a film is not present or broken. 10. The method of clause 9, wherein the detection intensity ratio PDR is measured and calculated in each of a plurality of exposure cycles, and the method further comprises: obtaining a measurement uncertainty value _δmeas associated with the measurement of the detection intensities; calculating the detection intensity ratio in exposure cycle n+1 The ratio of the detection intensity in the previous exposure cycle If , then the pellicle is determined to be complete in exposure cycle n + 1, where is equal to or greater than 11. The method of clause 10, wherein the determination that the membrane is complete includes overriding any determination that the membrane is not present or ruptured. 12. The method of clause 9, wherein the detection threshold Th is set to A value between 1 and 1. 13. The method of any one of clauses 8 to 12, further comprising obtaining a measurement uncertainty value δ _meas associated with the measurement of the detection strengths, wherein the detection threshold Th is set to ,in is equal to or greater than 14. The method of any one of clauses 8 to 12, further comprising: obtaining a reference second detection strength , which is the second detection intensity that can be measured when a reference patterning device is installed in the lithography apparatus and the pellicle is not installed in the lithography apparatus; and a reference detection intensity ratio PDR _meas is calculated as ; The detection threshold value Th is set to 15. The method of any one of clauses 2 to 14, further comprising: measuring and recording a transmittance value of the film at each of a plurality of time points; recording an exposure count x of the film when measuring each of the plurality of transmittance values; using the plurality of transmittance values and the plurality of exposure counts as input data to a prediction model, the prediction model predicting when the transmittance value of the film is expected to reach a replacement transmittance threshold value The remaining number of impressions before X. 16. The method of clause 15, wherein the calculated The detection intensity ratio PDR is used as the measured transmittance value of the surface film at each time point. 17. The method of clause 16, wherein the replacement transmittance threshold value is set to a value less than the detection threshold Th . 18. The method of any one of clauses 15 to 17, further comprising measuring and recording the hydrogen pressure surrounding the pellicle when measuring each of the plurality of transmittance values; wherein the input data further comprises a plurality of hydrogen pressure measurements. 19. The method of any one of clauses 15 to 18, further comprising measuring and recording the temperature of the pellicle or the temperature of the environment surrounding the pellicle when measuring each of the plurality of transmittance values; wherein the input data further comprises a plurality of temperature measurements. 20. The method of any one of clauses 15 to 19, wherein the prediction model predicts the remaining number of exposures by performing a regression analysis on the input data and extrapolating therefrom. 21. The method of clause 20, wherein the regression analysis comprises one or more of linear regression, quadratic regression, and exponential regression. 22. The method of any one of clauses 15 to 19, wherein the prediction model comprises a trained machine learning model. 23. The method of any one of clauses 15 to 22, further comprising applying a noise filter to the input data. 24. The method of clause 23, wherein the noise filter comprises a low-pass filter. 25. The method of any one of clauses 6 to 24, further comprising: at an initial time point t ₀ , measuring a reference first detection strength And measure the first detection strength The reference first detection intensity is the first detection intensity that can be measured when a reference stage alignment mark is installed in the lithography apparatus; at a subsequent time point t ₁ , the reference first detection intensity is remeasured. , and remeasure the first detection strength ; Set a drift factor Calculated as and at the subsequent time point t ₁ , before comparing the detection intensity ratio PDR with the detection threshold Th , by multiplying the detection intensity ratio by the drift factor 26. The method of any one of clauses 6 to 25, further comprising: measuring a reference first detection strength at an initial time point t ₂ . And measure the second detection strength The reference first detection intensity is the first detection intensity that can be measured when a reference stage alignment mark is installed in the lithography apparatus; at a subsequent time point t ₃ , the reference first detection intensity is remeasured. , and remeasure the second detection strength ; Set the second drift factor Calculated as and at the subsequent time point t ₃ , before comparing the detection intensity ratio PDR with the detection threshold Th , by multiplying the detection intensity ratio by the second drift factor 27. The method of clause 26, further comprising: at time point t3 _, making the second drift factor Associated with the patterning device and the pellicle mounted in the lithography apparatus, and storing the second drift factor ; dismantling the patterning device and the membrane; at a subsequent time point t ₄ after time point t ₃ , reinstalling the patterning device and the membrane and acquiring the second drift factor associated with the patterning device and the membrane 28. The method of any one of clauses 3 to 27, further comprising: at an initial time point t ₅ , measuring (which is the intensity _of the beam at time t5 ) and (which is the second detection intensity at time point t5 ); a system transmittance factor _at time _point t5 Calculated as At a subsequent time point t ₆ , measure (which is the intensity _of the beam at time t6 ) and (which is the second detection intensity at time point t ₆ ); the system transmittance factor at time point t ₆ Calculated as and before comparing the first detection intensity and the second detection intensity after _the subsequent time point t6 , by subtracting the second detection intensity from the first detection intensity. Multiply 29. The method of any one of clauses 2 to 28, wherein the lithography apparatus comprises a second alignment sensor, wherein the method further comprises: obtaining a sensitivity ratio , which is the sensitivity of the first alignment sensor and the sensitivity of the second alignment sensor A ratio between the two; using the second alignment sensor to measure , which is the intensity of light reflected from the patterned device alignment mark; With the sensitivity ratio Multiply to adjust ; and comparison and 30. The method of clause 29, wherein the exposure cycle m is measured , measured in exposure cycle m + 1 immediately following exposure cycle m , and the sensitivity ratio Set to 31. The method of clause 30, further comprising using the first alignment sensor to detect the pellicle in exposure cycle m + 2 following exposure cycle m + 1 , wherein the sensitivity ratio is set to zero only if the pellicle is detected to be intact in exposure cycle m + 2. Set to 32. The method of any one of clauses 2 to 31, wherein the patterning device includes a second patterning device alignment mark fixedly disposed thereon, wherein the method further comprises: obtaining an alignment mark intensity ratio I _markA /I _markB , where I _markA is the intensity of reflected light measurable from the first patterning device alignment mark and I _markB is the intensity of reflected light measurable from the second patterning device alignment mark under equal conditions; using the alignment sensor to measure I _ret,markB , which is the intensity of light reflected from the second patterning device alignment mark; and before comparing the first detection intensity and the second detection intensity, 33. The method of any one of clauses 2 to 32, wherein the first detection intensity and the second detection intensity are measured during a patterning device alignment operation. 34. The method of any one of clauses 2 to 33, wherein the steps of measuring the second detection intensity and comparing the first detection intensity and the second detection intensity are repeated at least once during each exposure cycle. 35. The method of any one of clauses 2 to 34, further comprising pausing the lithography apparatus after detecting that the pellicle is absent or ruptured. 36. The method of any one of clauses 2 to 35, wherein the lithography apparatus further comprises a dynamic air lock membrane (DGLm) intersecting both the optical path between the alignment sensor and the patterning device alignment mark and the optical path between the alignment sensor and the stage alignment mark, the method further comprising: obtaining a transmittance of the DGLm ; when the first detection intensity and/or the second detection intensity in an exposure cycle is detected to be increased compared with a previous exposure cycle ( ) times, determining that the DGLm has been broken. 37. A method as in any one of clauses 2 to 36, wherein the alignment sensor comprises a transmission image sensor. 38. A method as in any one of clauses 2 to 37, wherein: each of the stage alignment mark and the patterning device alignment mark comprises an orthogonal grating; the alignment sensor comprises a shearing interferometer phase stepping measurement sensor (PARIS); and the PARIS outputs a pixel array, each pixel having an offset component DC and a phase modulation component 39. The method of clause 38, wherein the first detection intensity and the second detection intensity Each of the above is derived from the offset component DC of the same pixel or pixel group. 40. The method of clause 38 or clause 39, wherein the first detection intensity and the second detection intensity Each of them is the phase modulation component from the same pixel or pixel group 41. The method of clause 40, wherein the first detection intensity and the second detection intensity Each of the first detection intensity is derived from the magnitude M of the phase modulation component of the same pixel or pixel group. and the second detection intensity Each of the above is derived from a linear combination of the offset component DC and the magnitude M of the phase modulation component for the same pixel or pixel group. 43. The method of any one of clauses 38 to 42, further comprising: using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group measurable from the stage alignment mark; using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group generated by light reflected from the alignment mark of the patterning device; calculating and monitoring The value of and ; Upon detection after having changed beyond a predetermined amount, determining that the measurements are unreliable. 44. The method of any one of clauses 38 to 43, further comprising averaging the pixel group. 45. The method of any one of clauses 38 to 44, wherein the pixel group is located at the center of the field of view of the PARIS. 46. The method of any one of clauses 38 to 45, wherein: the patterning device stage includes a plurality of stage alignment marks fixedly disposed thereon, and/or the patterning device includes a plurality of patterning device alignment marks fixedly disposed thereon; the PARIS includes a plurality of detectors for measuring light reflected from the patterning device stage and/or the plurality of alignment marks on the patterning device; and the first detection intensity and the second detection intensity Each of the detectors is derived from an average of the outputs from the plurality of detectors. 47. The method of any one of clauses 38 to 46, comprising: using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group generated by light reflected from the stage alignment mark; using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group generated by the light reflected from the alignment mark of the patterned device; the detection intensity ratio PDR is calculated as ,in and 48. A method as claimed in any one of clauses 38 to 47, wherein the first detection intensity and the second detection intensity is a field corresponding to the intensity value of the pixel array output by the PARIS, and the method further comprises determining the presence of and/or 49. The method of clause 48, further comprising comparing the Zernike aberrations in the second detection intensity of the current exposure to ... and the Zernike aberrations in the first detection intensity 50. The method of clause 48 or clause 49, further comprising comparing the Zöller aberrations in the second detection intensity of the current exposure 51. The method of any one of clauses 48 to 50, further comprising comparing the Zernike aberrations in the second detected intensity of the current exposure with the Zernike aberrations in the second detected intensity of the first exposure in the same exposure batch. 52. The method of any one of clauses 48 to 51, further comprising comparing the Zernike aberrations in the second detected intensity of the first exposure in the current exposure batch with the Zernike aberrations in the second detected intensity of the immediately preceding exposure. 53. The method of any one of clauses 48 to 52, further comprising comparing the Zernike aberrations in the second detected intensity of the current exposure in the current exposure batch with the Zernike aberrations in the second detected intensity of the last exposure in the immediately preceding exposure batch. 54. The method of any one of clauses 49 to 53, wherein the comparing the Zernike aberrations comprises calculating a difference between at least one Zernike term of the 2nd order, or the 3rd order, or higher, and optionally at least one Zernike term of the 5th order, or the 6th order, or higher. 55. The method of clause 54, further comprising: indicating that the pellicle is worn if the difference between the at least one Zernike term of the 2nd order, or the 3rd order, or higher, exceeds a predetermined threshold. 56. A method as described in any of the preceding clauses, wherein: measuring the first detection intensity includes measuring the intensity of light reflected from multiple locations of the patterned device, thereby generating a first detection map; measuring the second detection intensity is performed after measuring the first detection intensity and includes measuring the intensity of light reflected from the multiple locations of the patterned device, thereby generating a second detection map; and comparing the first detection intensity and the second detection intensity includes comparing the first detection map and the second detection map. 57. The method of clause 56, wherein each of the first detection map and the second detection map is offset from a reference detection map measured when the optical path between the alignment sensor and the patterning device intersects a different pellicle. 58. The method of clause 56 or clause 57, wherein comparing the first detection map and the second detection map comprises calculating a difference map by subtracting the first detection map and the second detection map from each other. 59. The method of clause 58, further comprising calculating a mean difference from the difference map. 60. The method of clause 59, further comprising determining that a pellicle is not present or ruptured if the mean difference exceeds a predetermined mean difference threshold. 61. The method of any one of clauses 58 to 60, further comprising converting the difference map into a histogram of difference values. 62. The method of clause 61, further comprising calculating a distribution width of the difference values from the histogram of difference values. 63. The method of clause 62, further comprising determining that a pellicle is not present or ruptured if the distribution width exceeds a predetermined distribution width threshold. 64. The method of clause 63, wherein the step of determining that a pellicle is not present or ruptured if the distribution width exceeds the predetermined distribution width threshold is performed only if it is determined that the mean difference does not exceed the predetermined mean difference threshold. 65. The method of any one of clauses 56 to 64, further comprising converting the first detection map and the second detection map into a first histogram and a second histogram of detection values, respectively. 66. The method of clause 65, further comprising: determining a first distribution pattern from the first histogram of detection values; and determining a second distribution pattern from the second histogram of detection values. 67. The method of clause 66, further comprising determining a diaphragm rupture if: the first distribution pattern is a unimodal distribution; and the second distribution pattern is a multimodal distribution. 68. The method of clause 66, further comprising determining a pellicle break if the following conditions exist: the first distribution mode is a unimodal distribution; and the second distribution mode is a bimodal distribution. 69. The method of any of the preceding clauses, wherein the pellicle is made of a material whose transmittance increases with the number of exposures. 70. The method of any of the preceding clauses, wherein the pellicle is made of a carbon nanotube material. 71. A method of manufacturing an apparatus comprising the steps of the method of any of the preceding clauses. 72. A computer program comprising instructions for causing a lithography apparatus to perform the method of any of clauses 1 to 70. 73. A lithography apparatus configured to perform the method of any of clauses 1 to 70.

While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

The above description is intended to be illustrative and not restrictive. Therefore, it will be apparent to those skilled in the art that modifications may be made to the invention as described without departing from the scope of the claims hereinafter set forth.

B: Radiation beam B': Light/patterned radiation beam BD: Beam delivery system C: Target part IL: Illumination system LA: Lithography equipment MA: Patterning device MAF: Patterning device alignment mark MP: pellicle MT: Patterning device stage/mask support MTF: Stage alignment mark PM: First positioner PS: Projection system PW: Second positioner SO: Radiation source W: Substrate WS: Alignment sensor WT: Substrate support

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference characters indicate corresponding parts.

Figure 1 schematically depicts a lithography apparatus.

Figure 2a schematically depicts light from the alignment marks of the patterning device passing through the surface film.

Figure 2b schematically depicts light from the patterned device stage alignment marks that does not pass through the surface film.

Figure 2c schematically depicts the light traveling along the alignment mark of the self-patterning device when no pellicle is present.

Figure 3 depicts the output signal of the shearing interferometer phase stepping measurement sensor.

Figure 4 depicts the predicted number of exposures remaining before the cover should be replaced.

Figures 5a to 5c depict various comparison schemes.

Figures 6a and 6b depict difference images of a surface film that was determined to be intact.

FIG7a and FIG7b depict difference images of a surface film that has been determined to be ruptured.

FIG8a and FIG8b depict difference images of another film that was determined to have ruptured.

The features shown in the drawings are not necessarily drawn to scale, and the sizes and/or configurations depicted are not limiting. It will be understood that the drawings include optional features that may not be essential to the present invention. In addition, not all features of the apparatus are depicted in each of the drawings, and the drawings may show only some of the components relevant for describing the particular feature.

B:Radiation beam

B': Light/Patterned Radiation Beam

MA: Patterned Installation

MAF: Patterned device alignment mark

MP: pellicle

MT: Patterned device stage/mask support

MTF: Stage Alignment Mark

Claims (26)

A method for performing pellicle monitoring using an alignment sensor of a lithography apparatus, wherein: the lithography apparatus includes a patterning device stage for supporting a patterning device; the patterning device stage includes a stage alignment mark fixedly disposed thereon; the patterning device includes a patterning device alignment mark fixedly disposed thereon; the alignment sensor is configured to use the patterning device alignment mark and the stage alignment mark to The method includes sensing alignment using an alignment mark; and the lithography apparatus is configured to position a pellicle so that the pellicle intersects a light path between the alignment sensor and the patterning device; wherein the method includes: measuring a first detection intensity using the alignment sensor; measuring a second detection intensity using the alignment sensor, the second detection intensity being the intensity of light reflected from the patterning device; and comparing the first detection intensity and the second detection intensity. The method of claim 1, wherein: the lithography apparatus is configured to position a pellicle such that the pellicle intersects an optical path between the alignment sensor and the patterning device alignment mark and does not intersect an optical path between the alignment sensor and the stage alignment mark; the first detection intensity is the intensity of the light reflected from the stage alignment mark; the second detection intensity is the intensity of light reflected from the alignment mark of the patterned device. The method of claim 2 further includes adjusting the relative position between a light beam and the patterned device stage so that: when measuring the first detection intensity, at least a portion of the light beam is incident on the stage alignment mark, and the reflection of the at least a portion is measured as the first detection intensity; and when measuring the second detection intensity, at least a portion of the light beam is incident on the patterned device alignment mark, and the reflection of the at least a portion is measured as the second detection intensity, and in the presence of the surface film, the portion of the light beam passes through the surface film. The method of claim 3 further comprising: measuring a first source intensity , which is the intensity of the light beam when measuring the first intensity; measuring a second source intensity , which is the intensity of the light beam when measuring the second intensity; a compensation factor is calculated as and before comparing the first detection strength and the second detection strength, by The second detection strength is adjusted by multiplying the compensation factor. The method of claim 3 or claim 4, wherein each of the patterned device alignment mark and the stage alignment mark is defined by a geometric arrangement of a reflective portion and an absorber portion, and the method further comprises: measuring , which is the intensity of light reflected from the absorber portion of the stage alignment mark; measuring , which is the intensity of light reflected from the absorber portion of the patterned device alignment mark; obtain the geometric factor , which is the ratio of the area of the absorber portion of the stage alignment mark to the total area of the stage alignment mark; the geometric factor is obtained , which is the ratio of the area of the absorber portion of the patterned device alignment mark to the total area of the patterned device alignment mark; before comparing the first detection intensity and the second detection intensity, by subtracting To adjust the first detection strength , and by subtracting To adjust the second detection strength . The method of any one of claims 2 to 4, wherein the comparing the first detection strength and the second detection strength comprises: calculating a detection strength ratio PDR , the detection strength ratio being the first detection strength With the second detection strength and comparing the detection intensity ratio with a detection threshold Th . The method of claim 6, further comprising: obtaining a transmittance of a reference film for the measured light , and based on The detection threshold Th is set. The method of claim 7, wherein the detection strength ratio PDR is calculated as , and the method further includes: if the detection intensity ratio PDR exceeds the detection threshold value Th , determining that a surface film does not exist or is broken. The method of claim 8, wherein the detection threshold Th is set to A value between 0 and 1. The method of any one of claims 2 to 4, wherein the transmittance threshold is replaced is set to a value less than the detection threshold Th . The method of claim 10, further comprising measuring and recording the hydrogen pressure surrounding the film when measuring each of the plurality of transmittance values; wherein the input data further comprises a plurality of hydrogen pressure measurements. The method of claim 10, further comprising measuring and recording the temperature of the pellicle or the temperature of the environment surrounding the pellicle when measuring each of the plurality of transmittance values; wherein the input data further comprises a plurality of temperature measurements. The method of any one of claims 2 to 4, wherein the lithography apparatus comprises a second alignment sensor, wherein the method further comprises: obtaining a sensitivity ratio , which is the sensitivity of the first alignment sensor and the sensitivity of the second alignment sensor A ratio between the two; using the second alignment sensor to measure , which is the intensity of light reflected from the patterned device alignment mark; With the sensitivity ratio Multiply to adjust ; and comparison and . The method of any one of claims 2 to 4, wherein the lithography apparatus further comprises a dynamic air lock diaphragm (DGLm) intersecting both the optical path between the alignment sensor and the patterning device alignment mark and the optical path between the alignment sensor and the stage alignment mark, the method further comprising: obtaining a transmittance of the DGLm ; when the first detection intensity and/or the second detection intensity in an exposure cycle is detected to be increased compared with a previous exposure cycle ( ) times, it is determined that the DGLm has been ruptured. The method of any of claims 2 to 4, wherein the alignment sensor comprises a transmissive image sensor. The method of any one of claims 2 to 4, wherein: each of the stage alignment mark and the patterning device alignment mark comprises an orthogonal grating; the alignment sensor comprises a shearing interferometer phase stepping measurement sensor (PARIS); and the PARIS outputs a pixel array, each pixel having an offset component DC and a phase modulation component . The method of claim 16, further comprising: using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group measurable from the stage alignment mark; using the PARIS to measure and , which are the magnitudes of the offset component and the phase modulation component of the pixel or pixel group generated by light reflected from the alignment mark of the patterning device; calculating and monitoring The value of and ; Upon detection The measurements are deemed unreliable after they have changed by more than a predetermined amount. The method of claim 16, wherein: the patterning device stage includes a plurality of stage alignment marks fixedly disposed thereon, and/or the patterning device includes a plurality of patterning device alignment marks fixedly disposed thereon; the PARIS includes a plurality of detectors for measuring light reflected from the patterning device stage and/or the plurality of alignment marks on the patterning device; and the first detection intensity and the second detection intensity Each of which is derived from an average of the outputs from the plurality of detectors. The method of claim 16, wherein the first detection intensity and the second detection intensity is a field corresponding to the intensity value of the pixel array output by the PARIS, and the method further comprises determining the presence of and/or The aberrations in the optical system include at least one Zernike term of the second, third, or higher order, wherein the order of the Zernike term is defined according to the Noll ranking scheme. The method of claim 19, further comprising comparing the Zernike aberrations in the second detection intensity of the current exposure and the Zernike aberrations in the first detection intensity . A method as in any one of claims 1 to 4, wherein: measuring the first detection intensity includes measuring the intensity of light reflected from multiple locations of the patterned device, thereby generating a first detection map; measuring the second detection intensity is performed after measuring the first detection intensity and includes measuring the intensity of light reflected from the multiple locations of the patterned device, thereby generating a second detection map; and comparing the first detection intensity and the second detection intensity includes comparing the first detection map and the second detection map. The method of claim 21, wherein comparing the first detection map and the second detection map comprises calculating a difference map by subtracting the first detection map and the second detection map from each other. The method of claim 21, further comprising converting the difference map into a histogram of difference values, and calculating a distribution width of the difference values from the histogram of difference values. The method of claim 21, further comprising determining that a pellicle is not present or is ruptured if a) the distribution width exceeds a predetermined distribution width threshold and/or b) the mean difference exceeds a predetermined mean difference threshold. The method of claim 21, further comprising converting the first detection map and the second detection map into a first histogram and a second histogram of detection values, respectively, and then determining a first distribution pattern from the first histogram of detection values; and determining a second distribution pattern from the second histogram of detection values. The method of claim 25, further comprising determining a diaphragm rupture if the following conditions exist: the first distribution mode is a unimodal distribution; and the second distribution mode is a multimodal distribution.