JP2010014439A - Flaw inspection device and flaw inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect a defect on or in each film by accurately controlling a focus position in a defect inspection in a laminated film structure.
A defect inspection apparatus (1) includes a refractive index measuring means (10) for measuring a refractive index on a wafer, a defect detection optical system (20) for acquiring image data of the wafer and detecting defects. A control unit (45) for classifying the measured refractive index for each film type and determining a focus position of the defect imaging optical system from the designed film formation information.
[Selection] Figure 4

Description

  The present invention relates to a defect inspection on a semiconductor wafer surface, and more particularly, to a defect inspection apparatus and a defect inspection method for optically inspecting a defect of a semiconductor wafer on which a circuit pattern is formed.

  Currently, there are two types of defect inspection apparatuses, a bright-field optical comparison apparatus and a laser scattering apparatus. The bright-field optical comparison type device compares the images captured by the CCD image sensor for each adjacent chip image by computer processing, and detects defects. At this time, a method has been proposed in which an autofocus optical system is provided separately from the imaging optical system, and the reflected light from the wafer surface is detected to obtain the in-focus position in real time (see, for example, Patent Document 1). In this method, based on the calculated focus position, the Z-axis of the stage holding the wafer is moved to image the wafer surface while adjusting the focal position on the wafer. A defect inspection is performed based on the acquired image data.

  The laser scattering type device detects scattered light from a defect while irradiating a laser, and detects a defect. The laser scattering type apparatus is generally suitable for detecting a foreign substance, but is weak for detecting a pattern defect. The greatest advantage of laser scattering devices is high throughput. The optical system is configured to detect abnormal scattered light, and the processing range such as the beam size and the pixel size is wider than that of the bright field optical comparison type apparatus, resulting in a difference in throughput.

  As for the defect inspection after Cu-CMP in which copper (Cu) deposited in the wiring groove of the interlayer insulating film is polished to complete the embedded wiring, it is best to perform the defect inspection immediately after Cu-CMP. is there. However, in practice, in order to prevent copper elution from the Cu wiring, defect inspection is performed after a SiC film of about 30 to 70 nm is formed after Cu-CMP. The purpose of defect inspection after Cu-CMP is to inspect scratches and particles generated in the Cu-CMP process. The SiC film formed on the Cu wiring is thin, and until now, inspection has been performed because it is within the depth of focus of the defect inspection apparatus.

  The surface of the Cu wiring is highly reflective and can be inspected relatively easily. On the other hand, in the portion without the Cu wiring, the lower wiring can be seen through the interlayer insulating film. In the defect inspection in the portion where there is no Cu wiring, the laser scattering apparatus does not scatter unless there is a defect such as a foreign substance on the film surface, and the focus position is difficult to narrow down. If there is a defect on the surface of the interlayer insulating film that can be seen through, the focus can be relied on the defect. However, if there is no defect or if there is a defect in the interlayer insulating film, focus on the interlayer insulating film part. Cannot match. For this reason, the focus is adjusted at the wiring portion when the recipe is created, and the focus value of the portion without wiring is set with the stage accuracy (focus accuracy) of the apparatus.

  The above-mentioned defocus is not a problem for chips and devices that have almost no area with very few wirings. However, in system LSIs for wireless devices using RFCMOS, there are extremely few thick interlayer insulating films of 1500 nm or more and Cu wiring. There is a layer. In this case, the focal position of the Cu wiring and the focal position of the interlayer insulating film through which the lower wiring can be seen are greatly different, and the conventional defect inspection deteriorates the focusing accuracy, and so-called defocusing frequently occurs.

  FIG. 1 and FIG. 2 are diagrams for explaining such problems of the prior art. As shown in FIG. 1A, if the auto-irradiation laser beam is irradiated at a Cu wiring 103 immediately below the SiC film 104, the laser beam is reflected without being transmitted. By detecting the reflected light 107 from the Cu wiring 103, the focal point position on the Cu surface can be accurately detected. At that time, an image obtained by the imaging system including the objective lens 105 is an appropriate image focused on the Cu wiring 103 on the surface as shown in FIG.

  However, when there is no Cu wiring 103 and the lower layer (front layer) Cu wiring 101 can be seen through the interlayer insulating film 102, the lower layer Cu wiring is focused, and so-called "focused" occurs.

  Specifically, as shown in FIG. 1B, the laser beam is transmitted through the transparent interlayer insulating film 102, resulting in an unstable focus, or as shown in FIG. 1C, the SiC film 104 and Through the interlayer insulating film 102, the lower Cu wiring 101 is focused. Even if the focus position is deviated, if a large defect is on the interlayer insulating film 102, the signal level is large even in defocusing, so that the defect can be focused and inspected at the focal point. If there is no large defect on 102 (even if there is a defect, it is a very fine defect), the lower layer Cu wiring 101 and a dummy pattern (not shown) will be focused.

  In the image obtained in such a state, as shown in FIG. 2B, only the lower Cu film 101 is clear, and correct image data in the layer of the Cu wiring 103 that is the current inspection object is obtained. Absent. Further, when the inspection is performed in a state where the lower layer Cu wiring 101 is in focus, the heroic or the like of the lower layer Cu wiring 101 is detected, which becomes a pseudo defect. As a result, the accuracy of defect detection decreases.

  In order to solve this, defects in the fine pattern layer on the transparent interlayer insulating film are detected with high sensitivity, while defects in the layer in which the lower layer pattern is formed are detected in a defocused state and originally inspected. There has been proposed a method that enables detection of only the defects in the process (for example, see Patent Document 2). In this method, in the optical path of the autofocus system provided separately from the imaging optical system, the incident angle to the wafer is irradiated at 85 degrees or more, preferably 88 degrees or more, and the reflected light is detected, and the imaging optics Adjust the focal position of the system.

  Focusing on the accuracy of inspection, it is ideal to perform defect inspection for each processing step. For example, when inspecting an increase in the number of defects due to the formation of an interlayer film, defect inspection can be performed before and after the film formation, and an increased sentence can be regarded as a defect increased by the film formation. However, this causes a problem that the number of processes increases.

In addition, in the present situation where the structure of the interlayer film is stacked, inspection cannot be performed for each process, and inspection is performed for processes that affect yield and for which defects are known by device management using bare wafers. As a result, the reliability of the product is ensured. Therefore, an inspection method that achieves both efficiency and accuracy of inspection is desired.
JP2003-177101A JP 2002-90311 A

  As described above, when performing defect detection on a wafer in which a conductor pattern that does not transmit light (for example, Cu wiring) and an interlayer insulating film through which the lower wiring can be seen are formed in the same layer, the focus position is accurately set. If appropriate image data can be obtained by controlling, defects on the SiC film, defects on the conductor pattern, and defects in the interlayer insulating film can be accurately captured, and the accuracy of defect inspection should be improved. is there.

  Therefore, it is an object to provide a defect inspection method and a defect inspection apparatus that accurately inspect defects on a conductor pattern formed on the same layer and defects on an interlayer insulating film with accurate focus control. .

  It is another object of the present invention to provide a defect inspection method capable of improving inspection efficiency.

In a first aspect, a defect inspection apparatus for optically detecting defects on a wafer is provided. This defect inspection device
A refractive index measuring means for measuring a refractive index on the wafer;
A defect detection optical system for detecting defects by acquiring image data of the wafer;
A control unit that classifies the measured refractive index for each film type and determines a focus position of a defect imaging optical system from designed film formation information;
Is provided.

  With the above configuration and method, the focus position can be accurately controlled, and defects on or in the film can be accurately captured. As a result, the accuracy of defect inspection is improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a diagram for explaining the basic concept of defect inspection according to the embodiment of the present invention.

  In the embodiment, prior to defect inspection in an arbitrary layer during the manufacturing process of a semiconductor device, a refractive index is measured on the wafer 51 to determine a focal position for defect inspection. By measuring the refractive index, the layer to be inspected is to be inspected for a defect on the conductor pattern (Cu wiring pattern 103, etc.), or the region without the pattern (interlayer insulating film 102, etc.) is to be inspected It can be specified whether it is present. That is, the type of the film to be subjected to the defect inspection is specified from the measured refractive index, and the film thickness is determined from the recipe (film formation) information of the film, thereby determining the focus position for the defect inspection.

  In the example of FIG. 3, after forming a Cu wiring (embedded wiring) 103 in the interlayer insulating film 102 by Cu-CMP, an SiC film 104a is formed as a protective film. The SiC film 104a is a film for preventing elution of copper (Cu) over time in defect inspection after Cu-CMP. In the region where the Cu wiring 103 is not present, the lower Cu wiring 101 can be seen through the SiC film 104 a and the interlayer insulating film 102. Note that the SiC film 104b is inserted in the lower layer Cu wiring 101 in order to detect defects in the layer.

  In this state, the refractive index is measured at the measurement location on the wafer 51 by the refractive index measuring mechanism 10. Whether the defect (foreign matter, particle, or scratch) on the conductor pattern (Cu wiring) 103 is to be detected in the layer to be inspected based on the refractive index, or the defect of the interlayer insulating film 102 without the Cu wiring 103 is detected. You can know what you are doing.

  The refractive index measurement mechanism 10 measures the refractive index of a film formed on the wafer 51 by, for example, a beam profile reflectometry (BPR) method or a VAR (Variable Angle Reflectometry) method. As an example, the refractive index of the Cu wiring 103 covered with the SiC film 104a, the refractive index of the interlayer insulating film 102 covered with the SiC film 104a, the refractive index of the lower Cu wiring 101 covered with the SiC film 104b, the SiC film 104b And the refractive index of the laminate of the interlayer insulating film 102 are measured. The measured refractive index of each film is classified and stored for each film type (each measurement value or each design value). By storing the refractive index for each film type, it is easy to determine which part on the wafer 51 is currently measured.

  Following the refractive index measurement mechanism 10, the defect detection optical system 20 including the objective lens 34 scans the wafer 51 and performs imaging for defect inspection. Prior to the imaging process, the focus position is determined based on the refractive index, so that image data can be acquired at an appropriate focus position.

  In parallel with the measurement of the refractive index by the refractive index measuring mechanism 10, it is desirable to confirm the focus reference position using an existing focusing optical system. In FIG. 3, the incident light I for focusing is irradiated on the wafer 51, the reflected light R from the wafer 51 is detected, and the surface position serving as the reference of the wafer 51 is grasped. When adjusting the focal position (focus position) in real time based on the refractive index measurement, the measured value may be greatly deviated for some reason, but by measuring the approximate reference position, Even when the value deviates greatly, the calculation of the focus position can be appropriately maintained.

  FIG. 4 is a schematic configuration diagram of the defect detection apparatus 1 having the refractive index measurement mechanism 10 of FIG. The refractive index measurement mechanism 10 includes, for example, a semiconductor laser 13, a beam splitter 14, an objective lens 15, a sensor 12, and a refractive index calculation unit 11. By measuring the incident angle dependency of the reflectance of light emitted from the semiconductor laser 13, the refractive index and the film thickness can be obtained.

  Specifically, when the light beam irradiated from the semiconductor laser 13 is condensed on the surface of the wafer 51 through the objective lens 15, the light beam focused on the wafer 51 is incident through the center of the objective lens 15. The component from the angle 0 ° to the component of the light ray passing through the end of the objective lens 15 is included, and these are incident on the wafer 51 at the same time. Multiple reflection of light occurs in the film of the wafer 51, and the reflected light changes according to the incident angle, film thickness, refractive index, and extinction coefficient. By projecting the reflected light transmitted through the beam splitter 14 onto the sensor 12, a reflection intensity distribution (profile) as a function of the incident angle can be obtained.

  The sensor 12 may be a single line sensor or may be configured to include two line sensors that are orthogonal to each other. The refractive index calculation unit 11 obtains a profile that most closely matches the measured reflectance distribution (profile) from the theoretical reflectance profiles based on the physical model by a curve fitting method or the like, and from the selected physical model, The refractive index is obtained and output as a refractive index measurement value. Along with the refractive index, the film thickness may be output as a measured value.

  The output of the refractive index measurement mechanism 10 is supplied to the calculation control unit 45. When the calculation control unit 45 receives the measured value of the refractive index, the calculation control unit 45 refers to the film formation information database (DB) 46 to determine whether the current measurement location is on the Cu wiring 103 (see FIG. 3) or the Cu wiring 103. It is determined whether it is a region of the interlayer insulating film 102 that does not exist or a bulk region other than that.

  The film formation information database 46 is information on which film thicknesses and various film thicknesses such as SiC films, SiO2 films, and SiOC films are formed in the semiconductor device manufacturing process. Or “film formation information”) in advance. In addition to the path information (film formation information), information about the refractive index of each layer is also stored in advance.

  FIG. 5 shows an example of the refractive index information that the film formation information database 46 has. FIG. 5A shows the measured refractive index values for each film type using a test piece (TP) having no actual circuit pattern. In the test piece, a SiC film having a thickness of 50 nm was formed on a silicon substrate, various films were formed thereon, and the film thickness and refractive index were measured by a film thickness measuring machine.

  The refractive index when a SiC film with a thickness of 50 nm is formed on a Cu wiring film is 1.888, and the refractive index when a SiOC film is formed with a thickness of 200 nm is 1.422 as a low-k film. The refractive index when an NCS film is formed as a film is 1.276, and the refractive index when an SiC film having a different composition and thickness is formed as a protective film on the NCS film is 1.896.

  FIG. 5B shows the result of the refractive index measurement using an actual product on which a conductor pattern is formed. The inspection is immediately after performing Cu-CMP. The refractive index when a 50 nm SiC film is formed on the Cu wiring is 1.8. Although not shown in the table, as a comparative example, the refractive index measurement was performed immediately after Cu-CMP and before film formation of SiC. As a result, the refractive index of the Cu wiring was 0. The refractive index on the dummy pattern region is 2.79, and the refractive index on the lower Cu wiring via the interlayer insulating film is 1.35.

  In order to confirm reproducibility, measurement was performed at three locations on the lower Cu wiring while moving the measurement spot in the lateral direction (horizontal direction) by 10 μm, and the measured values were 1.3596, 1.3596, 1.. It was 3597 and the repeatability was good. In measurement with an actual product, since a measurement spot may be located across the wiring, it is desirable to include an appropriate error in the measured value of the refractive index.

  By storing such refractive index information in the film formation information database 46 in advance, it is possible to specify which layer of which layer is currently measured from the result of refractive index measurement in defect inspection. .

  In the embodiment, as will be described later, the refractive index information measured at predetermined positions for each shot and for each wafer is sequentially stored in the film formation information database 46.

  Returning to FIG. 4, the arithmetic control unit 45 reads the type of film to be inspected and the film formation amount corresponding to the refractive index from the film formation information database 46, and calculates a focus value based on the film formation amount. This focus value is supplied to the stage controller 42.

  The output of the sensor 22 of the focusing optical system is also input to the stage controller 42. The sensor 22 receives a light beam irradiated from a second light source (for example, an infrared light source) 21 for focusing and reflected on the wafer 51, and detects a reference surface of the wafer 51. In the embodiment, the focus position is determined from the refractive index measurement value on the wafer and the film formation information of each film, but even if an unexpected situation such as the refractive index measurement value greatly deviates from the assumed range, A supplementary focusing optical system is used so that the focus value can be calculated appropriately.

  The defect detection optical system 20 follows the refractive index measurement mechanism 10 and detects a defect at a position where the refractive index is measured. The light beam emitted from the first light source 31 of the defect detection optical system 20 passes through the lens group 32, a part of which is reflected by the beam splitter 33, passes through a wave plate (not shown), and passes through the objective lens 34. The light enters the wafer 51 on the stage 50. The reflected light from the wafer 51 passes through the beam splitter 33 and forms an image on the image sensor 36 by the image lens 35.

  The image data acquired by the image sensor 36 is input to the image processing unit 41, and defect inspection is performed by a method of comparing defect coordinates, for example. The defect coordinate value specified by the image processing unit 41 may be fed back to the arithmetic processing unit 45 and output together with the focus value to an SEM that performs defect review or a microscope (not shown).

  As an operation, when the refractive index measured by the refractive index measuring mechanism 10 changes from the refractive index (1.8 ± allowable error) when the SiC film is formed on the Cu wiring, the arithmetic control unit 45 With reference to the film information database 46, the film configuration corresponding to the measured refractive index (for example, the laminated insulating film 102 on the lower Cu wiring 101) is specified, the film formation amount is read from the film formation information, and the film thickness The focus value corresponding to is calculated. The calculated focus value is supplied to the stage control unit 42.

  The stage control unit 42 can move the stage 50 in the Z-axis direction by an amount corresponding to the instructed focus value and focus on the same height as the surface of the uppermost Cu wiring 103. As a result, even if the lower layer Cu wiring 101 is focused by the output of the sensor 22 of the focusing optical system, the focus position can be returned to the correct focus position, and so-called “focus blurring” can be avoided.

  FIG. 6 is a flowchart showing the defect inspection method of the first embodiment. In the semiconductor device manufacturing process, Cu-CMP is performed (S11). After completion of the Cu-CMP process, a recipe instruction is received from a route information control unit (not shown), and a SiC film 104a for preventing Cu elution is formed by a film forming device (not shown) (S12). The wafer 51 is grounded on the stage 50 of the defect inspection apparatus 1, and the refractive index is measured on the wafer surface (S13).

  The calculation control unit 45 determines whether or not the measured value of the refractive index has changed from the measured value at the previous measurement location (S14). If there is no change, imaging for defect inspection is continued (S15). When the measured value of the refractive index changes, the film type information database 46 is referred to determine which film type the measured value belongs to. For example, it is determined whether the refractive index value is on the Cu wiring or the refractive index on the interlayer insulating film. In accordance with the determination result, the film thickness of the corresponding film is read from the film formation information to determine the focus value (S16). Based on the determined focus value, the stage position is adjusted, and imaging is continued while the focus position is appropriately adjusted (S15).

  Step S14 may be omitted, and the film type may be determined for each refractive index measurement value, and the corresponding focus value may be calculated.

  FIG. 7 is a schematic diagram illustrating an example of a refractive index measurement location. In this example, the location where the refractive index is measured in the first shot is different from the location where the refractive index is measured in the second shot, and the measurement data of the refractive index is overlapped to realize efficient measurement.

  Since the refractive index measurement is determined by the pattern that is formed, it is possible to increase the accuracy of expressing the pattern layout by measuring the chip, shot, and wafer in detail, but it takes time to measure everything finely. Not realistic. Therefore, since the shots on the wafer surface are the same, the refractive index measurement of the first shot is performed in increments of 5 μm, for example, and the measurement position of the refractive index is shifted by 1 μm horizontally in the second shot, and the third shot Further, the measurement is performed by shifting by 1 μm. Then, by superimposing the refractive index measurement results in each shot, the accuracy of the refractive index data is improved.

  In FIG. 7, only the configuration for shifting the refractive index measurement location for each shot is shown, but in addition to this, the refractive index measurement location may be different for each wafer. When the wafers have the same structure and the same layer, the measurement data collected for each wafer is accumulated and superimposed to obtain refractive index information that covers the wafer densely. Thereby, in the refractive index measurement in the latter half of the lot, the number of measurement points in the wafer and the frequency of the wafer to be measured (for example, once every two, once every three, etc.) can be lowered.

  Furthermore, the refractive index measurement result acquired for each layer can be accumulated with the measurement result of another layer by cooperation of the calculation control unit 45 and the film formation information database 46.

  FIG. 8 is a flowchart showing the defect inspection method of the second embodiment. In the example of FIG. 8, the refractive index is measured even before the SiC film 104a (see FIG. 3) is formed (before the inspection point). Ideally, it is desirable to form the SiC film 104a (see FIG. 3) immediately after Cu-CMP, but in a normal manufacturing process, an allowable grace time of about 12 hours is set after Cu-CMP. Therefore, the refractive index is measured using the grace time, a rough pattern in the shot is predicted in advance, and the time required for actual defect inspection is shortened.

  First, Cu-CMP is performed to flatten the Cu film, and a Cu wiring (embedded wiring) 103 is formed in the interlayer insulating film 102 (S21). Before forming the SiC film 104a, the refractive index is measured on the wafer surface (S22). This refractive index measurement may be performed at the same measurement location for each shot or for each wafer, or as described with reference to FIG. 7, by measuring at a measurement location different for each shot and / or for each wafer. Results may be superimposed.

  Next, the calculation control unit 45 refers to the refractive index information stored in the film formation information database 46, and predicts an approximate pattern layout from the measurement result (S23). For example, the measurement results are classified into roughly measured value groups, and the most recent (uppermost layer) Cu wiring 103 is distinguished from the other region (interlayer insulating film 102).

  The refractive index of the Cu wiring 103 without the SiC film 104a and the refractive index of the lower Cu wiring 101 through the interlayer insulating film 102 are respectively designed values (refractive index with the SiC film 104a present). Although the difference between the refractive index on the Cu wiring 103 exposed in the uppermost layer and the refractive index of the lower Cu wiring 101 is large, an approximate pattern layout on the wafer surface can be predicted.

  The arithmetic control unit 45 further reads the type of film (SiC film 104a in this example) and the film thickness formed on the Cu wiring 103 with reference to the path information (film formation information) in the film formation information database 46, A focus value after the formation of the SiC film 104a is determined (S24). Further, the position where the refractive index is measured by the defect inspection after forming the SiC film 104a is determined (S25). In this case, the measurement location after the deposition of the SiC film 104a is set to a location different from the measurement location before the deposition as described with reference to FIG. By obtaining the refractive index in two stages before and after the formation of the SiC film 104a, it is possible to efficiently collect measurement values and shorten the refractive index measurement time in actual defect inspection.

  In parallel with or before and after Steps S23 to S25, the film forming apparatus (not shown) receives a recipe instruction from the path and forms the SiC film 104a (S26). If the SiC film 104a is formed, the refractive index is measured at the refractive index measurement location determined in S25 (S27), and the focus value used in the defect inspection is determined (S28). The stage position is adjusted based on the determined focus value, and an image is picked up by the defect detection optical system 20 (S29).

  FIG. 9 is a flowchart showing the defect inspection method of the third embodiment. In the example of FIG. 9, defect inspection is performed at two focus positions on the Cu wiring 103 and on the SiC film 104a. In order to do this, before the SiC film 104a is formed, the focus value when focusing on the monitor pattern on the Cu wiring 103 or the wafer is measured, and the film of the SiC film 104a obtained from the film formation information is measured. Based on the thickness, a focus value for defect inspection on the SiC film 104a is determined.

  First, Cu-CMP is performed (S31), a focus position is measured on the Cu wiring 103 or a monitor pattern (not shown), and a reference focus value is determined (S32). The determination of the reference focus value may be performed using an existing focusing optical system (see FIG. 4). Usually, since a monitor pattern (for example, a 40 μm × 40 μm square area) for measuring the amount of Cu-CMP dishing is formed on the wafer, the reference focus value can be measured using the monitor pattern. .

  Next, the operation control unit 45 of the defect inspection apparatus 1 reads the film formation amount of the SiC film 104a with reference to the film formation information database 46, adds the film formation amount to the reference focus value of the Cu wiring 103, and The focus position on the SiC film 104a in the actual circuit area is determined (S33). The film formation amount is also used as a focus drive amount of the defect inspection apparatus 1, and based on this, the Z axis of the stage 50 is driven (S34).

  On the other hand, after measuring the focus position on the Cu wiring 103 or the monitor pattern, the wafer is set in a film forming apparatus (not shown), and the SiC film 104a is formed in accordance with a recipe instruction from the path (S35). After the film formation, the film thickness is measured on the monitor pattern using, for example, the refractive index measurement mechanism 10 (S36). This step may be skipped when the film formation information stored in the film formation information database 46 is used. A focus value on the SiC film 104a is obtained by adding the measured film thickness value or the film formation amount as an offset value to the focus value on the Cu wiring 103 or the monitor pattern.

  Next, in the defect inspection apparatus 1, imaging for defect inspection is performed at two focus positions on the surface of the Cu wiring 103 and the surface of the SiC film 104a in the monitor region and the circuit region by Z-axis driving (S34). (S37).

  The arithmetic control unit 45 records the detected defect location and the focus position at that time in the film formation information database (S38), and outputs it to the SEM or the like as necessary to review the defect location at two focus positions. (S39). In the SEM review, the defect inspection by the optimum focusing is realized by using the focus value on the Cu wiring 103 and the focus value on the SiC film 104a.

  According to this method, it is possible to focus on the surface of a thin film such as the SiC film 104 a on the Cu wiring 103. In the defect inspection by the conventional focusing optical system, it is possible to perform a more detailed defect inspection as compared with the case where the thickness of the thin film is handled within the error of the depth of focus.

  Further, the focus value on the Cu wiring 103 and the focus value on the SiC film 104a are recorded in the film formation information database 46, and two focus values are calculated by the calculation of two focus values at the next wiring layer inspection. Defect inspection and review can be performed using the four focus values obtained in one wiring layer. Depending on how the defect is imaged, it can be a hint to search in which layer the defect has occurred.

  10 and 11 are examples of images obtained when defect inspection is performed based on the focus value obtained by the method of the embodiment. In FIG. 10A, the uppermost Cu wiring 61 formed by the latest Cu-CMP is focused. Between the uppermost Cu wiring 61 and the Cu wiring 61, the lower Cu wiring 62 can be seen through the interlayer insulating film.

  10B, from the state of FIG. 10A, the defect inspection apparatus 1 measures the refractive index of the interlayer insulating film on the lower Cu wiring 62 (measures the refractive index in a region where the Cu wiring 61 is not present). ) This is an image when the Z-axis drive is performed and the focus is set on the lower Cu wiring 62 from the focus position on the Cu wiring 61. The defect inspection apparatus 1 determines that the surface position of the upper Cu wiring 61 is currently focused from the measurement result of the refractive index, and uses the thickness information of the interlayer insulating film on which the Cu wiring 61 is formed. Based on this, the focus position on the lower Cu wiring 61 can be determined.

  FIG. 11A shows an image when the lower dummy pattern 72 is in focus. The uppermost wiring pattern 71 appears blurred. In FIG. 11B, the defect inspection apparatus 1 measures the refractive index of the interlayer insulating film on the dummy pattern from the state of FIG. 11A and shows that the current focus position matches the lower dummy pattern. This is an image in which the Z axis is driven by about 2 μm from the film formation information and focused on the upper pattern 71.

  As described above, based on the measured refractive index information, the apparatus determines from the film formation information accumulated in the defect inspection apparatus 1 what laminated structure the measured location has. Then, the Z stage is moved to the boundary of the film structure, such as on the Cu wiring, SiC film, interlayer insulating film, etc., and the defect contrast signal is acquired, and the defect in the film is focused. Can do. Thereby, it is possible to observe defects between the lower layer Cu wiring and the nearest (uppermost) Cu wiring.

  FIG. 12 is a flowchart showing the stage drive based on refractive index measurement and the flow of image acquisition. First, the reference focus position is measured by the focusing optical system (21 and 22 in FIG. 4) of the defect inspection apparatus 1 (S101). Using this focus position as a reference, a refractive index is measured at a measurement location within the wafer surface (S102). The calculation control unit 45 refers to the film formation information database 46, compares the measured refractive index with the refractive index for each film type (S103), and extracts the focus offset value for each film (S104). The offset value (or focus value) is supplied to the stage controller 42 (S105), and the Z stage is driven (S106). An image for defect inspection is acquired at the focus position after the stage is driven (S107). A defect is detected from the acquired image (S108), and the defect inspection result is stored in a storage area such as a hard disk drive (S109). The stage is moved to the next inspection place (S110), and the process returns to step S101.

  FIG. 13 is a flowchart of another example showing the stage drive based on refractive index measurement and the flow of image acquisition. In this example, a defect inspection on the Cu wiring is targeted.

  First, the reference focus position is measured by the focusing mechanism (21 and 22 in FIG. 4) of the defect inspection apparatus 1 (S121). Using this focus position as a reference, a refractive index is measured at a measurement location within the wafer surface (S122). The arithmetic control unit 45 refers to the film formation information database 46 and compares the measured refractive index with the refractive index for each film type (S123).

  From the measurement result of the refractive index, it is determined whether or not the film configuration at the measurement location is a configuration in which a SiC film is formed on the Cu wiring formed by the latest Cu-CMP (S124). If the SiC film is not yet formed, the process advances to step S125 to set the current focus value as a reference value. That is, since the infrared rays of the focusing optical system are irradiated onto the Cu wiring, the arithmetic control unit 45 determines that the focus value is on the Cu wiring and sets this as the reference position A (S125). Further, the focus offset value A is determined from the film structure with reference to the film formation information database 46 (S126).

  On the other hand, if the SiC film is formed, the process proceeds to step S127, where the refractive index information stored in the film formation information database 46 is compared with the current measured refractive index value, and the Cu wiring exists. (S127), and based on the film formation information, the focus offset value B from the reference position (reference position B) measured in S121 is obtained (S128).

  Whether the SiC film is formed (S126) or after the film is formed (S128), an optimum stage position is obtained based on the respective reference position and offset position (S129). The Z stage movement amount for driving to the obtained stage position is sent to the stage controller 42 (S130), and the Z stage is moved (S131). At the position after the movement, an image for defect inspection is acquired (S132), and the defect is detected from the acquired image (S133). The result of the defect is stored in a storage device such as a hard disk drive (S134), and the stage is moved to the next inspection location (S135). Thereafter, the process returns to S121, and the process is repeated until the inspection at a predetermined location on the wafer is completed.

  As described above, according to the embodiment, in the defect inspection of the device in which the Cu wiring and the interlayer insulating film through which the lower layer wiring can be seen are formed in the same layer, the focus position is accurately controlled, It is possible to accurately capture defects on or in each film of the laminated film structure. As a result, the accuracy of defect inspection is improved.

The following notes are presented for the above explanation.
(Appendix 1)
A refractive index measuring means for measuring the refractive index on the wafer;
A defect detection optical system for detecting defects by acquiring image data of the wafer;
A control unit that classifies the measured refractive index for each film type and determines a focus position of a defect imaging optical system from designed film formation information;
A defect inspection apparatus comprising:
(Appendix 2)
A film formation information storage unit for storing film formation information including the refractive index and film thickness of each film;
The defect inspection apparatus according to appendix 1, further comprising:
(Appendix 3)
A stage controller that controls the position of the stage that holds the wafer based on the focus position;
The defect inspection apparatus according to appendix 1 or 2, further comprising:
(Appendix 4)
3. The defect inspection apparatus according to appendix 1 or 2, wherein the refractive index measurement mechanism measures a refractive index at a different location for each shot or wafer and superimposes the measured values of the refractive index.
(Appendix 5)
In the designed film configuration, pre-store film formation information including the refractive index and film thickness of each film;
Measuring the refractive index at a predetermined measurement location on the wafer; and
A step of obtaining a film formation amount at the measurement location based on the measured refractive index and the film formation information;
Determining a focus position for defect inspection of the wafer based on the film formation amount;
Acquiring an image on the wafer at the focus position and performing a defect inspection;
A defect inspection method comprising:
(Appendix 6)
The refractive index is measured at different points for each shot on the wafer or for each wafer,
Superimposing the refractive index data measured for each shot or for each wafer,
The defect inspection method according to appendix 5, characterized in that:
(Appendix 7)
The defect inspection is performed following the measurement of the refractive index on the wafer.
The defect inspection method according to appendix 5, characterized in that:
(Appendix 8)
6. The defect inspection method according to appendix 5, further comprising a step of identifying a film to be subjected to defect inspection by comparing the measured refractive index with the refractive index in the film formation information.

It is a figure for demonstrating the problem of the conventional defect inspection. It is a figure for demonstrating the problem of the conventional defect inspection. It is a figure for demonstrating the basic concept of the defect inspection of embodiment. It is a block diagram of the defect inspection apparatus of embodiment. It is a figure which shows the example of the refractive index information used by embodiment. It is a flowchart of the defect inspection method of the first embodiment. It is a figure which shows the example of the refractive index measurement location on a wafer. It is a flowchart of the defect inspection method of 2nd Example. It is a flowchart of the defect inspection method of the third time command. It is a figure which shows the example of the acquired image in the defect inspection of embodiment. It is a figure which shows the example of the acquired image in the defect inspection of embodiment. It is a flowchart of the stage drive and image acquisition in the defect inspection of the embodiment. It is a flowchart of the stage drive and image acquisition in the defect inspection of the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Defect inspection apparatus 10 Refractive index measuring mechanism 20 Defect detection optical system 21 Imaging light source 32 Lens group 34 Objective lens 36 Image sensor 41 Image processing part 42 Stage control part 45 Operation control part 46 Deposition information database (deposition information storage part) )
50 Stage 51 Wafer 61, 103 Nearest conductor pattern (Cu wiring)
62, 101 Lower layer conductor pattern (Cu wiring)
102 Interlayer insulating film 104a, 104b Protective film (SiC film)

Claims (6)

A refractive index measuring means for measuring the refractive index on the wafer;
A defect detection optical system for detecting defects by acquiring image data of the wafer;
A control unit that classifies the measured refractive index for each film type and determines a focus position of a defect imaging optical system from designed film formation information;
A defect inspection apparatus comprising: A film formation information storage unit for storing film formation information including the refractive index and film thickness of each film;
The defect inspection apparatus according to claim 1, further comprising: A stage controller that controls the position of the stage that holds the wafer based on the focus position;
The defect inspection apparatus according to claim 1, further comprising: In the designed film configuration, pre-store film formation information including the refractive index and film thickness of each film;
Measuring the refractive index at a predetermined measurement location on the wafer; and
A step of obtaining a film formation amount at the measurement location based on the measured refractive index and the film formation information;
Determining a focus position for defect inspection of the wafer based on the film formation amount;
Acquiring an image on the wafer at the focus position and performing a defect inspection;
A defect inspection method comprising: The refractive index is measured at different points for each shot on the wafer or for each wafer,
Superimposing the refractive index data measured for each shot or for each wafer,
The defect inspection method according to claim 4. The defect inspection is performed following the measurement of the refractive index on the wafer.
The defect inspection method according to claim 4.