TW202514286A - Calibration for a substrate topography measurement - Google Patents

Abstract

A method of obtaining a calibration for a substrate topography measurement, the method comprising: for each of a plurality of locations on a calibration substrate: obtaining a calibration substrate height reference value at the location; and obtaining a plurality of calibration substrate height measurement values at the location, each calibration substrate height measurement value corresponding to a measurement of a surface of the calibration substrate at the location, wherein a total number of the plurality of locations is greater than a total number of the plurality of calibration substrate height measurement values obtained at each location; the method further comprising: using the plurality of calibration substrate height measurement values obtained for each location, and the calibration substrate height reference values obtained for each location, to determine a plurality of calibration terms for the calibration substrate height measurement values.

Description

Calibration for substrate topography measurement

The present disclosure relates to methods and apparatus for obtaining calibrations for substrate topography measurement, and methods and apparatus for determining the topography of a substrate using the calibrations.

A lithography apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithography apparatus may be used, for example, in the manufacture of integrated circuits (ICs). A lithography apparatus may, for example, project a pattern (also often referred to as a "design layout" or "design") of a patterned device (e.g., a mask also known as a reticle) 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 been decreasing over the past few decades, while the number of functional components such as transistors per device has been increasing steadily, following a trend often referred to as "Moore's law." To keep pace with Moore's law, the semiconductor industry is pursuing technologies that enable the creation of smaller and smaller features. To project a pattern onto a substrate, lithography equipment can use electromagnetic radiation. The wavelength of this radiation determines the minimum size of the features patterned onto the substrate. Typical wavelengths currently used are 365 nm (i-line), 248 nm, 193 nm, and 13.5 nm. Lithography equipment using extreme ultraviolet (EUV) radiation having a wavelength in the range of 4 nm to 20 nm (eg, 6.7 nm or 13.5 nm) may be used to form smaller features on a substrate compared to lithography equipment using radiation having a wavelength of, for example, 193 nm.

Typically, a substrate may include multiple layers comprising one or more materials, each layer having been patterned by a reticle, and each of the layers may include multiple repetitions of the same pattern. The patterns of each layer may be arranged as a two-dimensional array. Any and all references to "substrate" should be understood to include a "base" substrate, such as a silicon or glass substrate or any other suitable base substrate and any layers disposed thereon, including but not limited to previously exposed and processed patterned layers and/or photoresists.

Different points across the surface of the substrate may be at different heights, and therefore, lithographic radiation focused on the surface of the substrate at a first point (at a first height) may not be focused at a second point (at a second height). To maintain focus on the substrate surface, the height of the surface of the substrate is measured, and corresponding adjustments of the lithography equipment are made.

A height measurement system may be used to measure the height of a surface of a substrate. However, it is known that light used by a height measurement system to measure the height of a surface of a substrate may partially penetrate into the substrate surface, rather than just reflect from the substrate surface. Partial reflection of the light may occur at layers below the surface of the substrate. This partial reflection causes errors in the substrate height measurement.

Substrate height measurement error may be referred to as height process dependency (HPD) or apparent surface deposition (ASD).

It may be desirable to provide a system that prevents or mitigates one or more of the problems associated with the prior art.

As described above, in order to maintain focus on the substrate surface, the height across the surface of the substrate is measured, which height is referred to herein as the topography of the substrate. Height measurement errors (e.g., height process dependency (HPD)) at a given location on the substrate surface can be reduced by optimizing the optical properties of the height measurement system (e.g., the spectrum of the light used for measurement, the angle of incidence, the focus, etc.). However, as the system is further optimized, these techniques become increasingly technically difficult. In addition, it is important to provide a solution for reducing height measurement errors that is generally applicable to any substrate.

The present disclosure thus provides methods and apparatus for determining calibrations for substrate topography measurements. Calibrations determined using physical calibration substrates and/or simulated calibration substrates can then be used to adjust topography measurements of production substrates to reduce or remove deviations of the measurements from true values due to height measurement errors.

As used herein, the term "calibration substrate" may refer to a substrate used for the purpose of obtaining a correction, and the term "production substrate" may refer to a substrate whose topography is to be corrected, for example, as part of an IC manufacturing process. For example, a production substrate may refer to one of a large number of production substrates in a large-scale production process. However, it should be understood that this terminology is generally arbitrary and is only used to distinguish substrates referred to in the methods and apparatus described and claimed herein.

According to the present disclosure, a method of obtaining a calibration for a substrate topography measurement is provided, the method comprising: for each of a plurality of locations on a calibration substrate: obtaining a calibration substrate height reference value at the location; and obtaining a plurality of calibration substrate height measurements at the location, each calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the location. A total number of the plurality of locations may be greater than a total number of the plurality of calibration substrate height measurements obtained at each location. The method may further comprise using the plurality of calibration substrate height measurements obtained for each location and the calibration substrate height reference values obtained for each location to determine a plurality of calibration terms for the calibration substrate height measurements.

Advantageously, the calibration methods described herein may be performed with respect to any substrate whose topography is to be determined, and may only need to be performed once for a given type of production substrate. Further advantageously, unlike some known methods of removing errors from the height measurement itself, the calibration methods described herein are not limited by the physical limitations of the system used to determine the calibration and/or substrate topography.

The correction substrate height reference value may be obtained by any suitable method to obtain a measurement of the correction substrate topography, which correction substrate topography may be assumed for the purposes of the methods described herein to be substantially the same as the true topography of the correction substrate. In applications where the correction substrate height reference value is obtained by measuring the height of a physical correction substrate at a number of locations on the correction substrate, such measurements may be slow and therefore unsuitable for use in high volume production processes. The methods described herein may thus enable all topography measurements of production substrates in a manufacturing process to benefit from accurate measurements of the correction substrate topography, while also achieving a high throughput of process substrates, since the height reference value need only be obtained once (on the correction substrate) and need not be obtained for each of the process substrates.

Similar to applications in which a physical calibration substrate is used, applications in which calibration substrate height reference values are obtained by simulation (i.e., based on a simulated calibration substrate) also achieve a high throughput of process substrates because only one substrate (the calibration substrate) needs to be simulated to obtain the calibration terms.

Multiple correction terms can be determined using multivariate regression.

The plurality of calibrated substrate height measurements may include one or more values corresponding to intensity measurements. For example, the one or more calibrated substrate height measurements may correspond to the intensity of a radiation beam reflected by the calibration substrate. In some examples, the reflected radiation may be divided into portions, and one or more of the calibrated substrate height measurements may correspond to the intensity of the one or more portions. In some examples, one or more of the calibrated substrate height measurements may correspond to the sum of the intensities of the one or more portions.

The plurality of calibrated substrate height measurements may include one or more values corresponding to polarized filtered measurements. For example, one or more radiation beams or portions of radiation beams reflected by the calibration substrate may pass through one or more polarization filters before being detected. In some examples, a plurality of calibrated substrate height measurements corresponding to the reflected radiation beam at a plurality of different polarizations may be obtained.

The plurality of calibration substrate height measurements may include one or more values corresponding to measurements obtained at different measurement wavelengths. For example, one or more radiation beams may be incident on the calibration substrate, and the one or more calibration substrate height measurements may correspond to the intensity of radiation at different wavelengths reflected by the calibration substrate. In some examples, the radiation beam incident on the calibration substrate may include broadband radiation. The measurement wavelength may include measurement of the radiation beam after reflection by the calibration substrate and filtering to select a specific wavelength. In some examples, multiple radiation beams, each having a different single wavelength (e.g., from one or more lasers), may be incident on the calibration substrate, and the intensities of the multiple radiation beams at different wavelengths may be detected after reflection by the calibration substrate.

The plurality of calibration substrate height measurement values may include values corresponding to measurements obtained using modulated radiation (e.g., wavelength modulated radiation). For example, obtaining the measurements using modulated radiation may include directing a wavelength modulated radiation beam (e.g., a wavelength modulated laser beam) having a wavelength modulated at a given frequency onto the calibration substrate at a location on the calibration substrate, and detecting a position of the wavelength modulated radiation beam at the location after the wavelength modulated radiation beam has been reflected from the calibration substrate, using detection based on the frequency of the modulation applied to the wavelength of the radiation beam to measure the modulation of the wavelength modulated radiation beam at the detected location.

Modulation of the detected position of the wavelength modulated radiation beam to detect the detected position may include using harmonics of the frequency of the modulation applied to the wavelength of the radiation beam.

The detection may be a lock-on detection which automatically selects between the first, second or other harmonics of the modulated frequency based on the amplitude of the harmonic.

The wavelength of the radiation beam can be modulated by up to 1/100 of the wavelength of the radiation beam.

The wavelength of the radiation beam can be modulated by up to 100 pm.

The radiation beam may be provided by a single frequency laser.

One or more of the calibration substrate height reference values may be simulated calibration substrate height reference values. For example, a simulated calibration substrate may be used to determine one or more of the calibration substrate height reference values.

One or more of the calibrated substrate height reference values may be obtained by measurement of the calibration substrate at the location (i.e., by physical measurement of the physical calibration substrate). For example, one or more of the calibrated substrate height reference values may be determined using barometric measurements, focus exposure matrix measurements, microscopy (e.g., atomic force microscopy, scanning probe microscopy, and/or scanning tunneling microscopy) measurements, or the like. Advantageously, obtaining the calibrated substrate height reference values (and/or calibrated substrate height measurement values) by measurement of a physical substrate enables the calibration of substrate topography measurements for any substrate using the methods described herein without requiring prior knowledge of the substrate properties.

One or more of the corrected substrate height measurements may be simulated corrected substrate height measurements. For example, a simulated corrected substrate may be used to determine one or more of the corrected substrate height measurements. In some examples, the simulated corrected substrate height measurements may be determined based on a corrected substrate height reference, where the corrected substrate height reference may be simulated and/or determined from measurements of a physical corrected substrate, as described herein. The simulated corrected substrate height measurements may be determined from simulations of any of the measurement techniques described herein for obtaining corrected substrate height measurements.

One or more of the correction substrate height measurements may be obtained by measuring the correction substrate at the location. For example, one or more of the correction substrate height measurements may be obtained by measuring a physical correction substrate according to one or more of the methods described herein for obtaining correction substrate height measurements.

In accordance with the present disclosure, a method of determining a topography of a production substrate is provided, the method comprising: obtaining a plurality of production substrate height measurements at a plurality of locations on a production substrate, each production substrate height measurement corresponding to a measurement of a surface of the production substrate at a respective one of the plurality of locations on the production substrate. The method may further comprise: receiving a set of correction terms obtained by the method described herein; and adjusting the production substrate height measurements based on the correction terms.

Advantageously, in the inventive method of determining the topography of production substrates, a single calibration (i.e., a set of calibration terms obtained for a calibration substrate) can be applied to all production substrates of the same type. Further advantageously, unlike some known methods of removing errors from the height measurement itself, applying the calibration described herein means that the removal (or correction) of height measurement errors is not limited by the physical limitations of the system used to determine the calibration and/or substrate topography.

The production substrate height measurements may be obtained using one or more of the methods described herein with respect to obtaining calibrated substrate height measurements, such that a set of production substrate height measurements corresponding to the calibrated substrate height measurements are obtained.

Further in accordance with the present disclosure, an apparatus for obtaining a calibration for a substrate topography measurement is provided. The apparatus may include: a support for supporting a calibration substrate; a projection unit configured to direct a radiation beam to a position on the calibration substrate; a moving mechanism operable to adjust the support and/or the projection unit so as to move the position on the calibration substrate at which the radiation beam is directed onto the calibration substrate; a detection system configured to detect the radiation after reflection by the calibration substrate, the detection system further configured to determine a calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the position; and one or more controllers configured to operate the moving mechanism so that the radiation beam is incident on a plurality of positions on the calibration substrate.

The one or more controllers may be further configured to, for each of the plurality of locations on the calibration substrate: receive a calibration substrate height reference value at the location; and receive a plurality of calibration substrate height measurements from the detection system, wherein a total number of the plurality of locations is greater than a total number of the plurality of calibration substrate height measurements received at each location. The one or more controllers may be further configured to use the plurality of calibration substrate height measurements received for each location and the calibration substrate height reference values received for each location to determine a plurality of correction terms for the calibration substrate height measurements.

Advantageously, the apparatus described herein can be used to obtain calibrations for any kind of substrate, without requiring prior knowledge of the substrate properties. Further advantageously, the calibration only needs to be performed once for a given type of production substrate. The apparatus described herein can thus enable all topography measurements of production substrates in a manufacturing process to benefit from accurate measurements of the calibration substrate topography, while also achieving a high throughput of process substrates, since the height reference value only needs to be obtained once (on the calibration substrate) and does not need to be obtained for each of the process substrates.

Additionally, calibrating substrate topography measurements using the apparatus described herein is not limited by the physical limitations of the projection and detection systems, or the projection and detection systems of the apparatus used to determine the topography of production substrates.

As described above, one or more of the correction substrate height reference values may be obtained by measurement of the correction substrate at the location (i.e., by physical measurement of the physical correction substrate). For example, one or more of the correction substrate height reference values may be determined using barometric measurement, focus exposure matrix measurement, microscopy (e.g., atomic force microscopy, scanning probe microscopy, and/or scanning tunneling microscopy) measurement, or the like, or by simulation. In some examples, the correction substrate height reference values may be determined using the apparatus described herein for obtaining calibrations for substrate topography measurement, but in other examples, the correction substrate height reference values may be obtained by other means.

The controller may be configured to determine the plurality of correction terms by means of multivariate regression.

The detection system can be configured to determine one or more corrected substrate height measurements corresponding to the intensity measurements. For example, the one or more corrected substrate height measurements can correspond to the intensity of the radiation beam reflected by the correction substrate. In some examples, the reflected radiation can be divided into parts (e.g., using appropriate optical elements, such as mirrors, filters, gratings, and the like), and one or more of the corrected substrate height measurements can correspond to the intensity of the one or more parts. In some examples, one or more of the corrected substrate height measurements can correspond to the sum of the intensities of the one or more parts.

The detection system can be configured to determine one or more calibrated substrate height measurements corresponding to polarized filtered measurements. For example, the apparatus can include one or more polarization filters, and the radiation beam reflected by the calibration substrate can pass through the one or more polarization filters before being detected by the detection system. In some examples, the detection system can be configured to obtain a plurality of calibrated substrate height measurements corresponding to the reflected radiation beam at a plurality of different polarizations (e.g., using a plurality of different polarization filters).

The detection system can be configured to determine one or more corrected substrate height measurements corresponding to measurements obtained at different measurement wavelengths. For example, one or more corrected substrate height measurements may correspond to the intensity of radiation at different wavelengths reflected by the correction substrate and detected by the detection system. In some examples, the projection unit can be configured to direct a radiation beam comprising broadband radiation onto the correction substrate. The measurement wavelength can include measurement of the radiation beam after reflection by the correction substrate and filtering to select a specific wavelength. For example, the device can include one or more narrowband pass filters, and/or diffraction gratings or prisms to achieve wavelength selection from the broadband radiation source. In some examples, the projection unit can be configured to direct multiple radiation beams, each having a different single wavelength (e.g., from one or more lasers), onto a correction substrate, and the detection system can be configured to detect the intensity of the multiple radiation beams at different wavelengths after reflection by the correction substrate.

The detection system may be configured to determine one or more calibration substrate height measurements corresponding to measurements obtained using modulated radiation (e.g., wavelength modulated radiation). For example, the projection unit may be configured to direct a wavelength modulated radiation beam (e.g., a wavelength modulated laser beam) having a wavelength modulated at a given frequency onto the calibration substrate at a location on the calibration substrate, and the detection system may be configured to detect the position of the wavelength modulated radiation beam at the location after the wavelength modulated radiation beam has been reflected from the calibration substrate, using detection based on the frequency of the modulation applied to the wavelength of the radiation beam to measure the modulation of the wavelength modulated radiation beam at the detected location.

The detection system may be configured to detect the modulation of the wavelength modulated radiation beam at the detected location using harmonics of the frequency of the modulation applied to the wavelength of the radiation beam.

The detection system may be configured to detect radiation using lock detection that automatically selects between the first harmonic, the second harmonic, or other harmonics of the modulated frequency based on the amplitude of the harmonic. For example, the detection system may include a lock amplifier.

The wavelength of the radiation beam can be adjusted up to 1/100 of the wavelength of the radiation beam.

The wavelength of the radiation beam can be adjusted up to 100 pm.

The radiation beam may be provided by a single frequency laser.

Further in accordance with the present disclosure, an apparatus for determining the topography of a produced substrate is provided. The apparatus may include: a support for supporting a production substrate; a projection unit configured to direct a radiation beam to a position on the correction substrate; a moving mechanism operable to adjust the support and/or the projection unit so as to move the position on the correction substrate at which the radiation beam is directed onto the production substrate; a detection system configured to detect the radiation after reflection by the position on the production substrate, the detection system further configured to determine a production substrate height measurement corresponding to a height of the production substrate at the position; and one or more controllers configured to operate the moving mechanism so that the radiation beam is incident on a plurality of positions on the production substrate.

The one or more controllers may be further configured to: receive a plurality of production substrate height measurements from the self-detection system; receive a set of correction terms; and adjust the production substrate height measurements based on the correction terms for each of the plurality of locations on the production substrate. The correction terms received by the one or more controllers may be obtained by the methods described herein. The correction terms received by the one or more controllers may be obtained using the apparatus described herein for obtaining calibrations for substrate topography measurements.

Advantageously, the apparatus described herein for determining the topography of production substrates enables a single calibration (i.e., a set of calibration terms obtained for a calibration substrate) to be applied to all production substrates of the same type. Further advantageously, the removal (or correction) of height measurement errors is not limited by the physical limitations of the apparatus.

In some examples, an apparatus for obtaining calibrations for substrate topography metrology may form part of an apparatus for determining the topography of a production substrate.

In general, it should be understood that the terms "calibration substrate height measurement" and "production substrate height measurement" as used herein may refer to values corresponding to measurements of calibration substrates and production substrates, respectively. Measurements of calibration substrates and/or production substrates may include, for example, measurements of the height of a guide substrate (i.e., at a position), measurements of height measurement errors, and/or intensity measurements or other types of measurements containing information related to the height of a substrate.

The locations on the production substrate where the production substrate height measurements are obtained should correspond to (eg, be the same or substantially the same as) the locations on the respective calibration substrates where the calibration substrate height measurements and calibration substrate height reference values are obtained.

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 365 nm, 248 nm, 193 nm, 157 nm or 126 nm) and EUV (extreme ultraviolet radiation, e.g., having a wavelength in the range of about 5 nm to 100 nm).

As used herein, the term “reticle,” “mask,” or “patterning device” may be broadly interpreted as referring to a general purpose patterning device that may be used to impart a patterned cross-section to an incident radiation beam that corresponds to a pattern to be produced in a target portion of a substrate.

FIG1 schematically depicts a lithography apparatus LA. The lithography apparatus LA comprises an illumination system (also referred to as an illuminator) IL configured to condition a radiation beam B (e.g., UV radiation, DUV radiation, or EUV radiation); a mask support (e.g., a mask stage) MT constructed 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 wafer stage) WT constructed 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 according to certain parameters; and a projection system (e.g., a refractive projection lens 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 (eg, comprising one or more dies).

In operation, the illumination system IL receives a radiation beam 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 to have a desired spatial and angular intensity distribution in a cross-section of the radiation beam 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 appropriate to the exposure radiation used and/or to other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, synthetic, magnetic, electromagnetic and/or electro-optical systems or any combination thereof. 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 may be covered by a liquid, such as water, having a relatively high refractive index, so as 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 US6952253, which is incorporated herein by reference.

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

In operation, a radiation beam B is incident on a patterning device (e.g. a mask) MA held on a mask support 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 the substrate W. By means of a second positioner PW and a position measurement system IF, the substrate support WT can be accurately moved, for example in order to position different target portions C at focused and aligned positions in the path of the radiation beam B. Similarly, a first positioner PM and possibly a further position sensor (which is 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 mask alignment marks M1, M2 and substrate alignment marks P1, P2 may be used to align the patterning device MA and the substrate W. Although the substrate alignment marks P1, P2 as shown occupy dedicated target portions, they may be located in the space between target portions. When the substrate alignment marks P1, P2 are located between target portions C, they are referred to as scribe line alignment marks.

To illustrate the present disclosure, a Cartesian coordinate system is used. A Cartesian coordinate system has three axes, namely, an x-axis, a y-axis, and a z-axis. Each of the three axes is orthogonal to the other two axes. A rotation about the x-axis is called an Rx rotation. A rotation about the y-axis is called an Ry rotation. A rotation about the z-axis is called an Rz rotation. The x-axis and the y-axis define a horizontal plane, while the z-axis is in a vertical direction. The Cartesian coordinate system is not limiting of the present disclosure and is only used for illustration. In fact, another coordinate system, such as a cylindrical coordinate system, can be used to illustrate the present disclosure. The orientation of the Cartesian coordinate system may be different, for example, so that the z-axis has a component along the horizontal plane. In the figures, the height of the substrate W is indicated as the Z direction.

The height measurement system LS is configured to measure the topography of the top surface of the substrate W. The height measurement system LS may be referred to as a level sensor or a topography measurement system. A map of the height (z) of the substrate as a function of the position (x, y) on the substrate may be generated from the measurements obtained using the height measurement system LS. This height map may then be used to adjust the vertical position of the substrate W and/or to adjust the projection system PS during projection of a pattern from the patterning device MA onto the substrate.

The height measurement system LS may be stationary. The substrate table WT and the substrate W may be moved in a scanning movement beneath the height measurement system LS. This allows the height measurement system to measure the height across the surface of the substrate W and thereby generate a height map.

The height measurement system LS comprises a projection unit 10, a detection system 12 and a processor 15. The projection unit 10 is configured to provide a light beam that is incident on a substrate W (including any patterned layers thereon) and then detected by the detection system 12. The position at which the light beam is incident on the detection system 12 depends on the height of the substrate W. This allows the height of the substrate W to be measured. The projection unit 10 comprises a diffraction grating (not depicted), which may be referred to as a projection grating. The detection system 12 comprises a diffraction grating (not depicted), which may be referred to as a detection grating. An image of the projection grating is formed at the diffraction grating, and this grating image provides a height measurement relative to the position of the detection grating.

The height measurement system LS may include multiple lasers (or other light sources). The height measurement system LS may, for example, include a broadband light source, such as a white light source that emits light across the visible spectrum. The height measurement system may, for example, include multiple lasers configured to emit light at different wavelengths. The output from the detection system 12 may be processed by a processor 15 to obtain a measured height of the substrate W. The measured height of the substrate may include height measurement errors. Height measurement errors may be caused by reflections of light from multiple layers of the substrate (as further explained below in conjunction with Figure 2). Height measurement errors may be referred to as height process dependence (HPD).

Height measurement error at a given position x on a substrate W during production Can be defined as: in is the height measurement value obtained by the height measurement system LS at position x on the substrate, and is the actual substrate topology or height at position x .

During metrology of substrate topography (also referred to as substrate or wafer map metrology), a plurality of values S1 ( _x ), S2 ( x ), ..., Sn ( x ) corresponding to measurements (or signals) from a height measurement system LS may be obtained at _each position x on the substrate (e.g., _{simultaneously} ). These values may correspond to, for example, the intensity of radiation reflected by the substrate, polarization filtered measurements, measurements obtained at different wavelengths, measurements obtained using modulated radiation, and/or any other kind of filtered measurement of substrate height.

The inventors of this case have found that the linear combination of equivalent values can be approximated : in Measure the reference height to be used The correction term may be determined by any suitable method for determining the morphology of the substrate. It should be understood that This can be determined by methods that are not suitable for execution on multiple production substrates (e.g., methods that are too slow or inefficient for high-volume production processes). However, according to the present disclosure, it may only be necessary to obtain Once, and therefore the resulting benefit of the improved ability to calibrate the HPD may therefore provide an acceptable trade-off in terms of time and resources. It may be determined, for example, from air pressure gauge measurements, focus exposure matrix measurements, microscopy (e.g. scanning tunneling microscopy) measurements, or the like. In some cases, simulation can be used to determine It is further proposed that principal component analysis can be used in linear combinations of signals to have a stronger fit, suppress potential noise and capture more information.

assumed For is a sufficient approximation, so that:

A plurality of height measurements (ie, substrate topography measurements) may be determined at a plurality of locations x ₁ , x ₂ , ..., x _m on the substrate. In the matrix formulation: in: , , , , .

For a given type of substrate, the correction term is obtained, for example, by simulation and/or based on height measurement of the physically corrected substrate. Once. For example, the lithography apparatus shown in FIG1 may further include a height measurement correction system ES. The height measurement correction system ES uses some of the same components as the height measurement system LS, and these components are indicated as common components in FIG1.

The height measurement correction system ES comprises a light source configured to generate a radiation beam. For example, the light source may be a single frequency laser. The single frequency laser may for example have a bandwidth of 10 MHz or less, for example a bandwidth of about 1 MHz. The light source may form part of the projection unit 10. The detection system 12 detects the reflection position of the laser beam.

Correction Item The update can be performed at given time intervals based on, for example, the reference height measurement data obtained. Advantageously, updating the correction term in this way can track process changes.

An example of a step or height sensor LS known in the art is schematically shown in FIG2 , which only illustrates the operating principle. The step or height sensor LS can also share several components with the height measurement correction system ES described herein. In the example shown in FIG2 , the step sensor comprises an optical system, which includes a projection unit LSP and a detection unit LSD. The projection unit LSP comprises a radiation source LSO (also referred to herein as light source), which provides a radiation beam LSB applied by a projection grating PGR of the projection unit LSP. The radiation source LSO may be, for example, a narrowband or broadband radiation source, such as a supercontinuum light source, polarized or non-polarized, pulsed or continuous, such as a polarized or non-polarized laser beam. The radiation source LSO may comprise a plurality of radiation sources with different colors or wavelength ranges, such as a plurality of LEDs. The radiation source LSO of the level sensor LS is not limited to visible radiation, but may additionally or alternatively cover UV and/or IR radiation and any wavelength range suitable for reflection from the surface of the substrate.

The projection grating PGR is a periodic grating comprising a periodic structure generating a radiation beam BE1 with a periodically varying intensity. The radiation beam BE1 with a periodically varying intensity is directed towards a measuring position MLO on the substrate W with an incident angle ANG between 0 and 90 degrees, typically between 70 and 80 degrees, relative to an axis (Z axis) perpendicular to the incident substrate surface. At the measuring position MLO, the patterned radiation beam BE1 is reflected by the substrate W (indicated by arrow BE2) and directed towards the detection unit LSD.

To determine the height level at the measuring position MLO, the level sensor further comprises a detection system comprising a detection grating DGR, a detector DET and a processing unit (not shown) for processing an output signal of the detector DET. The detection grating DGR may be equivalent to the projection grating PGR. The detector DET generates a detector output signal, which is indicative of the received light, for example indicating the intensity of the received light, such as a light detector, or representing the spatial distribution of the received intensity, such as a camera. The detector DET may comprise any combination of one or more detector types.

By means of triangulation techniques, the height level at the measurement location MLO can be determined. The detected height level is generally related to the signal strength as measured by the detector DET, which has a periodicity that depends inter alia on the design of the projection grating PGR and the (tilted) angle of incidence ANG.

The projection unit LSP and/or the detection unit LSD may comprise further optical elements such as lenses and/or mirrors (not shown) between the projection grating PGR and the detection grating DGR along the path of the patterned radiation beam.

In one embodiment, the detection grating DGR can be omitted and the detector DET can be placed where the detection grating DGR is located. Such a configuration provides a more direct detection of the image of the projection grating PGR.

In order to effectively cover the surface of the substrate W, the level sensor LS may be configured to project an array of measurement beams BE1 onto the surface of the substrate W, thereby generating an array of measurement areas MLO or light spots covering a larger measurement range.

Various height sensors of the general type are disclosed in, for example, US7265364 and US7646471, both of which are incorporated by reference. Height sensors that use UV radiation instead of visible or infrared radiation are disclosed in US2010233600A1, incorporated by reference. In WO2016102127A1, incorporated by reference, a compact height sensor is described that uses a multi-element detector to detect and identify the position of a grating image without detecting the grating.

Referring again to equation (4), the height measurement value (Matrix ) may correspond to a measurement of the height of the substrate W obtained by the triangulation technique described above with respect to the level sensor LS (wherein the height measurement may be determined by the height measurement calibration system ES with respect to the calibrated substrate). Height measurement value (Matrix ) may correspond to a measurement of the height of the substrate W obtained by measurement of the intensity of radiation reflected by the substrate W, a polarization filtered measurement, a measurement obtained at a different wavelength, a measurement obtained using modulated radiation, and/or any other type of filtered measurement of substrate height, as discussed above and discussed in more detail below. It should be understood that the terms "calibrated substrate height measurement" and "production substrate height measurement" as used herein may refer to height measurements. and/or altitude measurements .

Once the calibration substrate corresponding to a given type of production substrate has been determined, and , the correction term can be determined by solving equation (4) using multivariate regression (e.g., using the least squares method) The number of locations on the substrate should be greater than the number of calibrated substrate height measurements at each location, i.e. The larger the value of m , the better the fit.

Determine one or more production substrates corresponding to the calibration substrate and It should be understood that the calibration substrate and Before, after or simultaneously with the determination of and The production substrate can be judged in the same way as the calibration substrate. and The actual wafer morphology of each produced substrate can then be determined using the following formula: : .

In order to obtain calibrated substrate height measurements and production substrate height measurements at a plurality of positions on respective substrates W, the height measurement system LS and/or the height measurement correction system ES comprises a moving mechanism operable to adjust the measurement position MLO (i.e., the position on the substrate W at which the radiation beam BE1 is directed onto the substrate W) by moving the substrate support WT and/or the radiation source LSO. For example, the moving mechanism may comprise one or more actuators operable to move the support WT in the X-direction, the Y-direction, and/or the Z-direction, and/or one or more actuators operable to adjust the angle of the radiation source LSO and/or to move the radiation source LSO in the X-direction, the Y-direction, and/or the Z-direction. An example of a moving mechanism is the second positioner PW shown in FIG. 1 .

As discussed above, May include substrate height measurements corresponding to measurements obtained using modulated radiation. FIG3 illustrates an example of a height measurement correction system ES in more detail. As mentioned above, some components of the height measurement correction system ES may also form part of the height measurement system LS. In general, the projection unit 10 includes a light source 18 and is configured to direct a radiation beam 16 from the light source 18 onto an upper surface 22 of a substrate W (this substrate W may be a correction substrate for the purpose of obtaining correction items). The projection unit 10 may also include a diffraction grating 20. The diffraction grating 20, referred to as the projection grating 20, applies a periodic structure to the radiation beam 16. The radiation beam 16 is at an acute angle θ relative to a normal extending from the substrate W (in other words, relative in the Z direction).

The example height measurement system ES illustrated in FIG3 may be particularly useful for obtaining substrate height measurements corresponding to measurements obtained using modulated radiation. Substrate height measurements corresponding to measurements obtained using modulated radiation may correspond to height measurement errors (i.e., HPD). Although in the following description of FIG3 , the light source 18 is a single wavelength laser, it should be understood that other light sources may be used in addition to or in place of a single wavelength laser.

As shown in FIG3 , the locking amplifier 14 is configured to modulate the wavelength of the laser beam emitted by the projection unit 10. The locking amplifier 14 is further configured to receive an output signal from the detection system 12. The detected position of the reflected laser beam is modulated due to the wavelength modulation of the laser beam. The locking amplifier 14 provides an output that is a measure of the detected position modulation. The processor 15 uses the output from the locking amplifier to determine the height measurement error.

The laser 18 is configured to emit a laser beam 16 having a bandwidth of less than 2 nm, and may be referred to as a narrowband laser. The locked amplifier 14 applies modulation to the wavelength of the laser beam 16 emitted by the laser 18. The modulation may, for example, vary the wavelength of the laser beam 16 by approximately 1 pm. The modulation may vary the wavelength of the laser beam by up to 10 pm, for example up to 50 pm. The modulation may vary the wavelength by an amount greater than this, for example up to 100 pm. However, if a larger wavelength modulation, such as 100 pm, is used, the output from the locked amplifier 14 may no longer be linear (this will depend on the structure of the substrate).

Typically, the wavelength modulation may be up to 1/100 of the central wavelength of the laser beam 16 .

In general, the substrate W will include a number of patterned layers. However, for simplicity of description, the substrate W depicted in FIG. 3 has only two layers: a lower silicon layer 32 (which may be referred to as a "base" substrate) and an upper photoresist layer 30 (which may be referred to as an etch resist). The main portion 16a of the laser beam 16 is reflected from the upper surface 22 of the etch resist 30. The reflected main portion of the laser beam 16a is reflected toward the detection system 12.

The detection system 12 includes a diffraction grating 24 and a pair of detectors 26a, 26b. The diffraction grating 24 may be referred to as the detection grating 24. The reflected main portion of the laser beam 16a forms an image of the projected grating 20 at the detection grating 24. The detection grating 24 may have a periodicity that corresponds to the periodicity of the grating image formed by the reflected main portion of the laser beam 16a. The position of this grating image will depend on the height of the upper surface 22 of the resist 30. The detection grating 24 directs the laser light toward the first detector 26a and the second detector 26b. The ratio of laser light received by each detector 26a, 26b depends on the position of the grating image relative to the detection grating 24. Therefore, the signal output from the detectors 26a, 26b depends on the height of the upper surface 22 of the resist 30. A differential amplifier 28 can be used to determine the difference between the signals output from the detectors 26a, 26b. The output from the differential amplifier 28 is provided to the lock amplifier 14. Other position detection systems for detecting the position of the reflected laser beam can be used.

The projection unit 10 and the detection system 12 may include further optical elements such as lenses and/or mirrors (not depicted) along the path of the laser beam 16 (e.g. between the projection grating 20 and the detection grating 24).

As mentioned above, the main portion 16a of the laser beam is reflected from the upper surface 22 of the resist 30. However, the resist 30 is not a perfect reflector, and therefore a portion 16b of the laser beam 16 passes through the resist. This secondary laser beam portion 16b is reflected from the interface between the resist 30 and the silicon substrate 32. The secondary laser beam portion 16b is a relatively small proportion of the incident laser beam 16, such as 10% or less of the incident laser beam (e.g., 1% or less of the incident laser beam). This is schematically depicted by the secondary laser beam portion 16b being a thinner line than the main laser beam portion 16a.

The secondary laser beam portion 16b also forms an image of the projection grating 20 at the detector grating 24. However, this grating image is formed at a lower position than the grating image formed by the main laser beam portion 16a. As can be seen from FIG. 3, the position of the detector grating image provided by the secondary laser beam portion 16b is determined by the height of the silicon substrate 32. The height offset between the position of the grating image provided by the main laser beam portion 16a and the position of the grating image provided by the secondary laser beam portion 16b will depend on the thickness T of the resist.

The grating image formed by the secondary laser beam portion 16b introduces a measurement error into the signal output by the self-detectors 26a, 26b. The signal output by the self-detectors 26a, 26b will indicate that the height of the upper surface 22 of the resist is lower than the actual height of the upper surface of the resist. The height measurement correction system ES determines this height measurement error.

The measurement obtained by the height measurement calibration system ES shown in FIG3 is now explained in more detail with reference to FIG3. The optical path difference L between the primary laser beam portion 16a and the secondary laser beam portion 16b can be expressed as: The reflected laser beam 16, considered as a single beam, has a complex amplitude: Where A is the amplitude of the main laser beam portion 16a and a is the amplitude of the secondary laser beam portion 16b. It can be assumed that 𝑛 ₁ 1 and 𝑛 ₁ ≈𝑛 ₂ ( n ₁ is the refractive index of the resist 30 and n ₂ is the refractive index of the silicon substrate 32). Therefore, it can be assumed that the reflection 16b from the silicon substrate 32 is weaker than the reflection 16a from the resist 30. At A , the phase of the reflected laser beam 16 is: In the assumption In the case of , the height measurement error HPD caused by the secondary laser beam portion 16b can be expressed as: Equation 9 includes the following terms: This indicates that the height measurement error HPD will oscillate depending on the wavelength of the laser beam 16. The disclosed embodiment obtains information about the height measurement error HPD by applying modulation to the wavelength of the laser beam 16.

The locking amplifier 14 modulates the signal that controls the operation of the laser 18 so that the wavelength of the laser beam 16 is modulated. The modulation is at a given frequency (e.g., selected by the user or automatically selected by the locking amplifier). This results in a modulation of the position of the reflected laser beam 16 detected by the detectors 26a, 26b.

The locked amplifier 14 uses the frequency of the modulation applied to the laser beam to measure the modulation of the detected position of the laser beam 16. The locked amplifier is configured to identify harmonics (e.g., first harmonics) of the signal output from the operational amplifier 28 (or other output signals in the case of using a different position detection system). The locked amplifier 14 identifies the harmonics as components of the output signal that have a frequency that is a harmonic of the modulation applied to the laser 18. The locked amplifier 14 provides an output signal having an amplitude that is indicative of the amplitude of the detected harmonic. The processor 15 receives the output signal from the locked amplifier 14. The processor 15 uses the output signal to determine a height measurement error.

In some cases, the first harmonic of the signal received by the locking amplifier may have a lower amplitude than, for example, the second harmonic. The relative amplitudes of the different harmonics will depend on the refractive index and thickness of the anti-etching agent layer 30 in the scenario depicted in Figure 3. The locking amplifier 14 can be configured to automatically select the harmonic that provides the maximum signal amplitude. In other scenarios (not depicted) where the substrate is provided with more layers, the relative amplitudes of the different harmonics will depend on the refractive index and thickness of each layer. In addition, the locking amplifier 14 can be configured to automatically select the harmonic that provides the maximum signal amplitude. For example, for some substrates, the first harmonic can provide a strong signal that can be used to determine height measurement errors. For other substrates, the second harmonic may provide a strong signal that can be used to determine height measurement errors. Other harmonics may be used. Generally, lock detection automatically selects between the first harmonic, the second harmonic, or other harmonics of the modulated frequency based on the amplitude of the harmonic.

Generally speaking, lock detection is used to measure the modulation of a modulated wavelength laser beam at a detected position (such as detected by detectors 28a, 28b). Lock detection is achieved by modulating the laser beam at a given frequency and then using that frequency to identify the modulation of the detected position. The modulation of the laser beam and the lock detection can both be performed by the lock amplifier 14.

In one embodiment, the broadband light source (or other light source) of the height measurement system LS can be arranged adjacent to the laser 18 of the height measurement calibration system ES. In this case, the projection grating 20, the detection grating 24, and the detector 26 can be common between the two systems. The systems LS and ES can be operated simultaneously. That is, the height measurement system LS can measure the height map of the substrate W (which can correspond to the matrix ), and the height measurement correction system ES can also determine the height measurement error (which can form a matrix part of).

In the scenario depicted in FIG. 3 , the determined adjustment may be an absolute measure of the height measurement error HPD , i.e., a value indicating the offset between the measured height of the upper surface 22 of the resist 30 and the actual height of the upper surface of the resist. Referring to equation (10), the refractive index n ₂ of the resist 30 is known, the incident angle θ of the laser beam 16 is known, and the wavelength λ of the laser beam is known. The relative amplitudes a , A of the first laser beam portion 16a and the second laser beam portion 16b may be measured during calibration. Therefore, the height measurement error HPD may be considered as an absolute value that depends on the only unknown T.

Typically, more than 200 dies are exposed on the substrate, and in some cases, more than 600 dies are exposed on the substrate. Each of the dies has been exposed using the same series of patterning device exposures and has undergone the same processing. Therefore, each of the dies should have the same properties, including the same height measurement error. In practice, the height measurement error may vary across the substrate. This may occur, for example, due to the effects of processing of the substrate layer. In one example, metal may be deposited into a structure formed in the substrate, and excess metal may be removed from the substrate using polishing. Polishing may, for example, remove slightly more material from one side of the substrate compared to the opposite side of the substrate (e.g., there may be a gradient of metal thickness across the substrate). Embodiments of the present disclosure may provide output height measurement error values that vary gradually across the surface of the substrate.

As an alternative or in addition to the value corresponding to the measurement obtained using modulated radiation (i.e., the height measurement error value), May include measurements of the intensity of radiation detected by the detection system 12. In some examples, Polarized filtered measurements may be included. For example, the height measurement system LS and/or the height measurement correction system ES may include one or more polarized filters positioned in the path of the radiation beams BE1, BE2, 16, 16a, 16b. The polarized filters may be controllable or selectable by a controller, which may include a processor 15. In some examples, Measurements obtained at different wavelengths may be included. For example, the light source 18 may include multiple single wavelength light sources, and/or one or more gratings, prisms and/or filters may be positioned in the path of the radiation beams BE1, BE2, 16, 16a, 16b to achieve wavelength selection. The wavelength may be selected by a controller that may include a processor 15.

In order to effectively cover the surface of the substrate W, embodiments of the present disclosure may be configured to project an array of laser beams 16 onto the surface of the substrate W. This provides an array of measurement regions on the substrate that covers a larger measurement range.

The described embodiments of the present disclosure include a height measurement system LS and a separate height measurement calibration system ES. However, in one embodiment, a single system may be used. That is, the height measurement calibration system ES may determine height measurement errors and may also provide substrate height measurements.

Embodiments of the present invention are described as including a single frequency laser having a bandwidth of 10 MHz or less (e.g., a bandwidth of about 1 MHz). Embodiments of the present invention may include a single frequency laser having a bandwidth of up to 20 MHz. Such embodiments may provide useful height measurement errors. However, the dynamic range of such embodiments will be less than a single frequency laser having a narrower bandwidth.

The theory behind the correction technique disclosed in this article will now be described.

For a given substrate (e.g. a wafer stack), the height measurement error HPD may have a wavelength dependency. This wavelength dependency is strongly substrate dependent and cannot be easily predicted. In known methods for determining the topography of a substrate, a weighted average of this wavelength dependency curve is typically used to obtain the substrate height measurement. Since the weighting is fixed, small changes in the substrate result in small changes in the HPD curve, which in turn causes changes in the HPD (in detail, inter-field and intra-field HPD). In the method according to the present disclosure, an additional measurement signal is obtained (i.e., If the HPD curve varies randomly, there is no correlation between these signals and the total HPD. However, on typical substrates, the HPD variation across the wafer (both between fields and within fields) is typically small. Therefore, the variation in the HPD curve is expected to be small, and the variation measured by the additional signal shows a correlation with the total HPD and can therefore be used to correct for the variation. The methods disclosed herein may therefore be particularly applicable to correcting for HPD variations within a wafer, such as between fields and within fields HPD, which are advantageously the types of HPD that have the greatest impact on the focus of the height measurement system.

FIG4 illustrates an example of a method 400 for obtaining a calibration for substrate topography measurements according to the present disclosure. For example, the method 400 may be performed by the processor 15 illustrated in FIG3 , wherein the processor 15 may form part of a controller to control one or more elements of the height measurement system LS and/or height measurement calibration system ES described herein. Alternatively or additionally, the method may be performed with respect to a simulated calibration substrate, and one or more of the measurements of the method 400 may be simulated measurements.

In step S402 of method 400, for each of a plurality of positions (e.g., x ₁ , x ₂ , . . . , x _m ) on the calibration substrate, a calibration substrate height reference value (e.g., ).

In step S406 of method 400, for each of a plurality of locations on the calibration substrate, a plurality of substrate height measurements are obtained at the location (e.g. and/or S1 ( x ), S2 ( x ), ..., Sn ₍ x )). _Each calibration substrate height measurement value corresponds to a height measurement of the surface of the calibration substrate at that position. The total number of the plurality _of positions should be greater than the total number of the plurality of calibration substrate heights obtained at each position (i.e., ).

In step S408 of method 400, a plurality of correction terms (e.g., ). Multiple correction terms can be determined by multivariate regression.

Figure 5 shows an example of a method 500 for determining the topography of a production substrate. For example, the method 500 may be performed by the processor 15 shown in Figure 3, where the processor 15 may form part of a controller to control one or more components of the height measurement system LS and/or the height measurement calibration system ES described herein.

In step S502 of method 500, a plurality of production substrate height measurements are obtained at a plurality of locations on the production substrate. Each production substrate height measurement corresponds to a height measurement of a surface of the production substrate at a respective location among the plurality of locations on the production substrate.

In step S504 of method 500, a set of correction terms is received. The set of correction terms may have been determined by method 400 illustrated in FIG. 4 and/or using substrate height correction system ES. In some examples, the set of correction terms may be stored in a memory and may be provided as an input, for example, to processor 15 (i.e., retrieved from memory).

In step S506 of method 500, the production substrate height measurement is adjusted based on the correction term. The adjusted production substrate height measurement may provide a measurement of substrate topography that is closer to the true substrate topography than may be achieved using known methods and techniques for reducing height measurement errors.

To demonstrate the effectiveness of the correction techniques described in this disclosure, the results of a simulated determination of height measurement error (HPD) will now be presented and discussed. For simulation purposes, a simulation of a real production substrate comprising a stack of 14 layers with different thicknesses was produced.

Monte Carlo simulations are performed to calculate 100 different substrates with small variations based on known tolerances of layer thicknesses of production substrates. As described herein, the simulated height of the substrate can be considered as a substrate height reference value.

For each of the 100 simulated substrates, a height measurement value (signal) from the height measurement system LS is calculated, as well as nine additional substrate height measurements: a substrate height measurement value (signal) corresponding to the height measurement error (as described above with reference to FIG. 3 ), and a first harmonic lock signal (providing the local slope of the HPD curve) and a second harmonic lock signal (providing the local curvature of the HPD curve) are calculated at three different laser wavelengths (300 nm, 350 nm, and 400 nm). The nine additional substrate height measurements for the 100 simulated substrates are plotted in FIG. 6( a) to FIG. 6( c ), where the horizontal axis shows the calculated different HPD values, which are obtained by subtracting the calculated height of each substrate from the average substrate height of the 100 substrates.

From the height measurement values, 10 correction parameters are calculated. Next, the HPD correction is calculated using different sets of 100 Monte Carlo simulations. Figure 7(a) shows the field-to-field HPD variation across a simulated substrate for a correction based on only three substrate height measurement error signals (the top curves of each of Figures 6(a) to 6(c); the "three additional signals") and based on all nine of the "additional signals" described above. When only three substrate height measurement error signals are used in addition to the height measurement values from the height measurement system LS, an 83% reduction in HPD is achieved. When nine signals (including the first and second harmonics) are used, a 94% reduction in HPD is achieved. FIG. 7( b ) shows similar results for the second mock substrate stack, where a 56% reduction in HPD and a 98% reduction in HPD are achieved for three additional signals and nine additional signals, respectively.

Although the methods described herein have been described with respect to a substrate W that has been or will be exposed to lithographic radiation (i.e., radiation beam B), it will be apparent to those skilled in the art that the methods (and corresponding apparatus) may be advantageously adapted for use with substrates that are not exposed to lithographic radiation.

In the described embodiments of the invention, wavelength modulation and harmonic detection are performed by a locked amplifier. However, any suitable device may be used to apply the wavelength modulation, and any suitable device may be used to detect the harmonics of the applied modulation. Generally, any of homodyne detection, heterodyne detection, and quadrature detection may be used. These are examples of locked detection. Detection may use hardware or software.

A height metrology system and/or a height metrology correction system may be referred to as an apparatus for obtaining a calibration for substrate topography measurement and/or an apparatus for determining the topography of a production substrate.

Embodiments of the present disclosure may form part of a lithography apparatus (such as depicted). Embodiments of the present disclosure may form part of a lithography tool. Examples of lithography tools are further mentioned below.

Likewise, although the methods described herein have been described with respect to DUV lithography radiation, as will be apparent to those skilled in the art, such methods (and corresponding apparatus) may be beneficially adapted for use with EUV lithography radiation (and corresponding apparatus).

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. Possible other applications include the manufacture of integrated optical systems, guidance and detection for magnetic resonance memory, flat panel displays, liquid crystal displays (LCDs), thin film magnetic heads, and the like.

Although specific reference may be made herein to embodiments of the present disclosure in the context of lithography apparatus, embodiments of the present disclosure may be used in other apparatus. Embodiments of the present disclosure may form part of a mask inspection apparatus, a metrology apparatus, or any apparatus that measures or processes an object such as a wafer (or other substrate) or a mask (or other patterned device). Such apparatus may generally be referred to as a lithography tool. Such lithography tools may use vacuum conditions or ambient (non-vacuum) conditions.

Although the foregoing may specifically refer to the use of embodiments of the present disclosure in the context of optical lithography, it should be understood that the present disclosure is not limited to optical lithography where the context permits, and may be used in other applications such as imprint lithography or in applications related to optical distance measurement or optical profiling of surfaces of multi-layer materials.

Where the context permits, embodiments of the present disclosure may be implemented in hardware, firmware, software, or any combination thereof. Embodiments of the present disclosure may also be implemented as instructions stored on a machine-readable medium that may be read and executed by one or more processors (e.g., processor 15) that may form part of a controller. A machine-readable medium may include any mechanism for storing or transmitting information in a form that can be read by a machine (e.g., a computing device). For example, machine-readable media may include read-only memory (ROM); random access memory (RAM); magnetic storage media; optical storage media; flash memory devices; electrical, optical, acoustic or other forms of propagation signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. In addition, firmware, software, routines, instructions may be described herein as performing certain actions. However, it should be understood that such descriptions are merely for convenience, and such actions are in fact caused by a computing device, processor, controller or other device executing the firmware, software, routines, instructions, etc., and doing so may cause actuators or other devices to interact with the real world.

Although specific embodiments of the present disclosure have been described above, it should be understood that the present disclosure may be practiced in other ways than those described. The above description is intended to be illustrative and not restrictive. Thus, it will be apparent to one skilled in the art that the present disclosure may be modified as described without departing from the scope of the claims set forth below. Other aspects of the present invention are set forth in the following numbered clauses. 1.   A method for obtaining a calibration for a substrate topography measurement, the method comprising: For each of a plurality of locations on a calibration substrate: Obtaining a calibration substrate height reference value at the location; and Obtaining a plurality of calibration substrate height measurements at the location, each calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the location, wherein a total number of the plurality of locations is greater than a total number of the plurality of calibration substrate height measurements obtained at each location; The method further comprises: Using the plurality of calibration substrate height measurements obtained for each location and the calibration substrate height reference values obtained for each location to determine a plurality of calibration terms for the calibration substrate height measurements. 2.   The method of clause 1, comprising determining the plurality of calibration terms by means of multivariate regression. 3.   The method of clause 1 or 2, wherein the plurality of calibrated substrate height measurements include one or more values corresponding to an intensity measurement. 4.   The method of any of the preceding clauses, wherein the plurality of calibrated substrate height measurements include one or more values corresponding to a polarization filtered measurement. 5.   The method of any of the preceding clauses, wherein the plurality of calibrated substrate height measurements include values corresponding to measurements obtained at different measurement wavelengths. 6.   The method of any of the preceding clauses, wherein the plurality of calibrated substrate height measurements include values corresponding to measurements obtained using modulated radiation. 7.   The method of any of the preceding clauses, wherein one or more of the calibrated substrate height reference values are analog calibrated substrate height reference values. 8.   A method as in any of the preceding clauses, wherein one or more of the calibration substrate height reference values are obtained by measuring a height of the calibration substrate at the location. 9.   A method as in any of the preceding clauses, wherein one or more of the calibration substrate height measurement values are simulated calibration substrate height measurement values. 10.   A method as in any of the preceding clauses, wherein one or more of the calibration substrate height measurement values are obtained by measuring a height of the calibration substrate at the location. 11. A method for determining a morphology of a production substrate, the method comprising: obtaining a plurality of production substrate height measurements at a plurality of locations on a production substrate, each production substrate height measurement corresponding to a measurement of a surface of the production substrate at a respective one of the plurality of locations on the production substrate; receiving a set of correction terms obtained by a method as in any of the preceding clauses; and adjusting the production substrate height measurements based on the correction terms. 12. An apparatus for obtaining a calibration for a substrate topography measurement, the apparatus comprising: a support for supporting a calibration substrate; a projection unit configured to direct a radiation beam to a position on the calibration substrate; a movement mechanism operable to adjust the support and/or the projection unit to move the position on the calibration substrate at which the radiation beam is directed onto the calibration substrate; a detection system configured to detect the radiation after reflection by the position on the calibration substrate, the detection system further configured to determine a calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the position; and One or more controllers configured to operate the moving mechanism so that the radiation beam is incident on a plurality of positions on the calibration substrate; wherein the one or more controllers are further configured to, for each of the plurality of positions on the calibration substrate: receive a calibration substrate height reference value at the position; and receive a plurality of calibration substrate height measurements from the detection system, wherein a total number of the plurality of positions is greater than a total number of the plurality of calibration substrate height measurements received at each position; and wherein the one or more controllers are further configured to use the plurality of calibration substrate height measurements received for each position and the calibration substrate height reference values received for each position to determine a plurality of correction items for the calibration substrate height measurements. 13.  The apparatus of clause 12, wherein the controller is configured to determine the plurality of correction terms by means of multivariate regression. 14.  The apparatus of clause 12 or 13, wherein the detection system is configured to determine a corrected substrate height measurement corresponding to one or more of: an intensity measurement; a polarization filtered measurement; measurements obtained at different wavelengths; measurements obtained using modulated radiation. 15. An apparatus for determining a morphology of a production substrate, the apparatus comprising: a support for supporting a production substrate; a projection unit configured to direct a radiation beam to a position on the production substrate; a moving mechanism operable to adjust the support and/or the projection unit to move the position on the production substrate at which the radiation beam is directed onto the production substrate; a detection system configured to detect the radiation after reflection by the position on the production substrate, the detection system further configured to determine a production substrate height measurement corresponding to a measurement of a surface of the production substrate at the position; and One or more controllers configured to operate the motion mechanism so that the radiation beam is incident on a plurality of locations on the production substrate; wherein the one or more controllers are further configured to: receive a plurality of production substrate height measurements from the detection system for each of the plurality of locations on the production substrate; receive a set of correction terms obtained by the method of any of clauses 1 to 10; and adjust the production substrate height measurements based on the correction terms.

10: projection unit 12: detection system 14: locking amplifier 15: processor 16: laser beam/incident laser beam/reflected laser beam/laser beam array 16a: main laser beam portion/main portion/first laser beam portion/radiation beam 16b: secondary laser beam portion/portion/second laser beam portion/radiation beam 18: light source/laser 20: bypass grating/projection grating 22: upper surface 24: bypass grating/detection grating/detector grating 26a: detector/first detector 26b: detector/second detector 28: differential amplifier/operational amplifier 30: anti-etching agent/upper photoresist layer/anti-etching agent layer 32: Lower silicon layer/silicon substrate 400: method 500: method ANG: incident angle B: radiation beam BD: beam delivery system BE1: patterned radiation beam/radiation beam/measuring beam BE2: arrow C: target portion DGR: detection grating DET: detector ES: height measurement correction system/system/substrate height correction system IF: position measurement system IL: illumination system/illuminator LA: lithography equipment LS: height measurement system/system LSB: radiation beam LSD: detection unit LSO: radiation source LSP: projection unit MA: patterning device/mask MLO: measurement position/measurement area MT: mask support/mask stage M ₁ : mask alignment mark M ₂ : mask alignment mark n ₁ : refractive index n ₂ : refractive index PM: first positioner PGR: projection grating PS: projection system/refractive projection lens system PW: second positioner P ₁ : substrate alignment mark P ₂ : substrate alignment mark S402: step S406: step S408: step S502: step S506: step S508: step SO: radiation source T: thickness W: substrate WT: substrate support/substrate stage/support X: direction Y: direction Z: direction θ: sharp angle/incident angle

An embodiment of the present disclosure will now be described with reference to the accompanying drawings as examples only, in which: - FIG. 1 schematically depicts a lithography apparatus according to the present disclosure including a system for determining substrate height measurement errors; - FIG. 2 schematically depicts an example of a height measurement system and/or a height measurement correction system according to the present disclosure; - FIG. 3 schematically depicts an example of a height measurement correction system according to the present disclosure in more detail; - FIG. 4 schematically depicts a method for obtaining a correction for substrate morphology measurement according to the present disclosure; - FIG. 5 schematically depicts a method for obtaining the morphology of a production substrate according to the present disclosure; - FIG. 6(a) to FIG. 6(c) show simulated substrate height measurement values obtained for a simulated substrate; and - Figures 7(a) and 7(b) show the height measurement errors across a set of simulated substrates using different total numbers of substrate height measurements.

400:Method

S402: Step

S406: Step

S408: Step

Claims (15)

A method for obtaining a correction for a substrate topography measurement, the method comprising: For each of a plurality of locations on a calibration substrate: Obtaining a calibration substrate height reference value at the location; and Obtaining a plurality of calibration substrate height measurements at the location, each calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the location, wherein a total number of the plurality of locations is greater than a total number of the plurality of calibration substrate height measurements obtained at each location; The method further comprises: Using the plurality of calibration substrate height measurements obtained for each location and the calibration substrate height reference values obtained for each location to determine a plurality of correction items for the calibration substrate height measurements. The method of claim 1, comprising determining the plurality of correction terms by means of multivariate regression. The method of claim 1 or 2, wherein the plurality of calibrated substrate height measurements include one or more values corresponding to an intensity measurement. The method of claim 1 or 2, wherein the plurality of calibrated substrate height measurement values include one or more values corresponding to a polarized filtered measurement. A method as claimed in claim 1 or 2, wherein the plurality of calibrated substrate height measurement values include values corresponding to measurements obtained at different measurement wavelengths. The method of claim 1 or 2, wherein the plurality of calibrated substrate height measurement values include values corresponding to measurements obtained using modulated radiation. The method of claim 1 or 2, wherein one or more of the calibrated substrate height reference values are simulated calibrated substrate height reference values. A method as claimed in claim 1 or 2, wherein one or more of the calibration substrate height reference values is obtained by measuring a height of the calibration substrate at the position. The method of claim 1 or 2, wherein one or more of the corrected substrate height measurements are simulated corrected substrate height measurements. A method as claimed in claim 1 or 2, wherein one or more of the calibration substrate height measurements are obtained by measuring a height of the calibration substrate at the location. A method for determining a morphology of a production substrate, the method comprising: obtaining a plurality of production substrate height measurements at a plurality of locations on a production substrate, each production substrate height measurement corresponding to a measurement of a surface of the production substrate at a respective one of the plurality of locations on the production substrate; receiving a set of correction terms obtained by a method as in any of the preceding claims; and adjusting the production substrate height measurements based on the correction terms. An apparatus for obtaining a calibration for a substrate topography measurement, the apparatus comprising: a support for supporting a calibration substrate; a projection unit configured to direct a radiation beam to a position on the calibration substrate; a movement mechanism operable to adjust the support and/or the projection unit to move the position on the calibration substrate at which the radiation beam is directed onto the calibration substrate; a detection system configured to detect the radiation after reflection from the position on the calibration substrate, the detection system further configured to determine a calibration substrate height measurement corresponding to a measurement of a surface of the calibration substrate at the position; and One or more controllers configured to operate the moving mechanism so that the radiation beam is incident on a plurality of positions on the calibration substrate; wherein the one or more controllers are further configured to, for each of the plurality of positions on the calibration substrate: receive a calibration substrate height reference value at the position; and receive a plurality of calibration substrate height measurements from the detection system, wherein a total number of the plurality of positions is greater than a total number of the plurality of calibration substrate height measurements received at each position; and wherein the one or more controllers are further configured to use the plurality of calibration substrate height measurements received for each position and the calibration substrate height reference values received for each position to determine a plurality of correction items for the calibration substrate height measurements. The apparatus of claim 12, wherein the controller is configured to determine the plurality of correction terms by means of multivariate regression. The apparatus of claim 12 or 13, wherein the detection system is configured to determine a calibrated substrate height measurement corresponding to one or more of: an intensity measurement; a polarization filtered measurement; a measurement obtained at different wavelengths; a measurement obtained using modulated radiation. An apparatus for determining a morphology of a production substrate, the apparatus comprising: a support for supporting a production substrate; a projection unit configured to direct a radiation beam to a position on the production substrate; a moving mechanism operable to adjust the support and/or the projection unit to move the position on the production substrate at which the radiation beam is directed onto the production substrate; a detection system configured to detect the radiation after reflection by the position on the production substrate, the detection system further configured to determine a production substrate height measurement corresponding to a measurement of a surface of the production substrate at the position; and One or more controllers configured to operate the motion mechanism so that the radiation beam is incident on a plurality of locations on the production substrate; wherein the one or more controllers are further configured to: receive a plurality of production substrate height measurements from the detection system for each of the plurality of locations on the production substrate; receive a set of correction terms obtained by the method of any one of claims 1 to 10; and adjust the production substrate height measurements based on the correction terms.