Pattern inspection apparatus, focus position adjustment method, and pattern inspection method

Abstract

The pattern inspection device according to one embodiment of the present invention is characterized by comprising: a related data creation circuit, in a state in which an evaluation substrate on which an evaluation pattern is formed is placed on a table, an autofocus signal serving as a parameter for autofocus control for each height position and a focus evaluation value for evaluating the focus position are acquired while changing the height position of a pattern formation surface of the evaluation substrate. Making related data of the automatic focusing signal and the focusing evaluation value; the automatic focus signal calculation circuit for inspection uses an automatic focus signal and a focus evaluation value for each height position, which are acquired while changing the height position of a pattern forming surface of a substrate to be inspected in a state where the substrate to be inspected on which a graphic pattern is formed is placed on a table, and related data of an evaluation substrate. Calculating an auto-focus signal for inspection that obtains a focus evaluation value greater than or equal to a threshold value on the substrate to be inspected; and an autofocus mechanism for adjusting the height position of the pattern forming surface of the substrate to be inspected to the height position of the pattern forming surface corresponding to the value of the autofocus signal for inspection.

Description

Technical Field

[0001] This application claims priority based on JP2023-175426 (application number), filed in Japan on October 10, 2023. The entire contents set forth in JP2023-175426 are incorporated herein by reference.

[0002] This invention relates to a pattern inspection apparatus, a focus position adjustment method, and a pattern inspection method. For example, it relates to an apparatus for inspecting pattern defects in exposure masks used in semiconductor manufacturing, and a focus position adjustment method for the apparatus. Background Technology

[0003] In recent years, with the increasing integration and capacity of large-scale integrated circuits (LSI), the required circuit linewidths for semiconductor devices have become increasingly narrow. These semiconductor devices are manufactured by using a primary image pattern (also known as a mask or intermediate mask, hereinafter collectively referred to as a mask) with circuit patterns to expose and transfer the pattern onto a wafer using a shrinking projection exposure device known as a step-out exposure device, thereby forming a circuit.

[0004] Furthermore, improving yield is essential for LSI manufacturing, which involves significant production costs. One major reason for declining yield is pattern defects in the masks used during the exposure and transfer of ultra-fine patterns on semiconductor wafers using photolithography. In recent years, with the miniaturization of LSI patterns formed on semiconductor wafers, the dimensions that must be inspected for pattern defects have also become extremely small. Therefore, there is a need for high-precision pattern inspection equipment to check for defects in the transfer masks used in LSI manufacturing.

[0005] As inspection methods, there are, for example, "die-to-die inspection" and "die-to-database inspection." "Die-to-die inspection" compares optical image data obtained from photographing the same pattern at different locations on the same mask with each other. "Die-to-database inspection" converts the CAD data of the pattern design into drawing data (design data) in the device input format used when drawing the pattern on the mask, inputs it into the inspection device, generates a reference image based on this, and compares it with the optical image of the measurement data obtained from photographing the pattern.

[0006] In this inspection apparatus, a clear image of the pattern on the mask, which serves as the object to be inspected, needs to be acquired. However, due to the limited depth of focus in the optical system of the inspection apparatus, the surface of the object to be inspected must be continuously kept within the depth of focus during inspection. In other words, the contrast of the captured image must be kept within an acceptable range. Currently, the inspection apparatus requires continuous image capture by scanning the mask while moving the stage, and then calculating the image contrast sequentially to adjust the focus of the optical system during inspection. This is impractical due to insufficient processing time.

[0007] Therefore, in addition to the inspection optical system for image capture, the inspection device also employs an autofocus mechanism that detects the displacement of the object being inspected relative to the inspection optical system in the height direction and adjusts its height position.

[0008] With the recent miniaturization of patterns, the wavelength of inspection light continues to shorten. Consequently, the focal depth of the inspection optical system becomes shallower. Therefore, the accuracy of the measurement system using a separate autofocus mechanism located near the inspection optical system is sufficient. However, without in-situ measurements utilizing the inspection optical system itself, it is impossible to detect various variations in the inspection optical system (dependence on temperature / mechanical deformation), and high-precision focus adjustment is not possible. Therefore, as an autofocus mechanism, a method utilizing part of the inspection optical system is adopted (for example, see Patent Document 1).

[0009] In the optical system of this autofocus mechanism, the amount of light passing through slits positioned before and after the focal point of the image from the mask is measured, and the difference between the two measured light amounts is calculated, thereby measuring the change in the height position of the mask. Here, an error arises between the height position where the difference in measured light amounts is zero and the height position where the image contrast is at its maximum. Therefore, it is necessary to obtain the parameters required for the autofocus operation that maximizes the image contrast for each mask being inspected. On the other hand, to obtain the parameters required for the autofocus operation that maximizes the image contrast, data relating the two is needed, and the process of obtaining this relational data takes time. To shorten inspection time and thus increase throughput, it is necessary to shorten the time spent on the process of obtaining the parameters required for the autofocus operation that maximizes the image contrast.

[0010] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2020-125941 Summary of the Invention

[0011] The problem that the invention aims to solve Therefore, one aspect of the present invention provides an inspection apparatus and method capable of acquiring the parameters required for the automatic focusing operation of the substrate being inspected in a shorter time than before.

[0012] Methods for solving problems One aspect of the pattern inspection apparatus of the present invention is characterized by comprising: a worktable for holding a substrate; a drive mechanism for moving the height position of the worktable; a correlation data generation circuit that, while the evaluation substrate having an evaluation pattern formed thereon is placed on the worktable, generates correlation data between the autofocus signal (a parameter for autofocus control at each height position) and the focus evaluation value (for evaluating the focus position) by acquiring autofocus signals for each height position and the focus evaluation value while the height position of the pattern forming surface of the evaluation substrate is variable; a storage device for storing the correlation data; and an inspection autofocus signal calculation circuit that, while the inspection substrate having a graphic pattern formed thereon is placed on the worktable, generates correlation data between the autofocus signal and the focus evaluation value by acquiring autofocus signals for each height position and the autofocus signal for each height position; and an inspection autofocus signal calculation circuit that, while the height position of the pattern forming surface of the inspection substrate is variable while the autofocus signal is variable, generates correlation data between the autofocus signal and the focus evaluation value; and a storage device for storing the correlation data; and an inspection autofocus signal calculation circuit that, while the inspection substrate having a graphic pattern formed thereon is placed on the worktable, generates correlation data between the autofocus signal and the focus evaluation value. The system comprises: an autofocus signal for inspection that yields an autofocus evaluation value above a threshold in the inspected substrate, obtained from the autofocus signal and focus evaluation value at each height position, and related data of the inspected substrate; an autofocus mechanism that adjusts the height position of the pattern forming surface of the inspected substrate to the height position of the pattern forming surface corresponding to the value of the autofocus signal for inspection; a sensor that receives light transmitted or reflected from the inspected substrate by the inspected substrate illuminated by the inspected light, thereby capturing an optical image of the inspected substrate, while the height position of the pattern forming surface of the inspected substrate is adjusted to the height position of the pattern forming surface corresponding to the value of the autofocus signal for inspection; and a comparison circuit that compares the captured optical pixels with a reference image.

[0013] One aspect of the focus position adjustment method of the present invention is characterized by using an autofocus signal (used as a parameter for autofocus control) and a focus evaluation value (used for evaluating the focus position) obtained while the evaluation substrate with an evaluation pattern is placed on a worktable, and while the height position of the pattern forming surface of the evaluation substrate is variable, to generate correlation data of the autofocus signal and the focus evaluation value, storing the correlation data in a storage device, and using the autofocus signal and focus evaluation value obtained while the inspection substrate with a pattern is placed on a worktable, and while the height position of the pattern forming surface of the inspection substrate is variable, along with the correlation data of the evaluation substrate, to calculate an inspection autofocus signal that obtains a focus evaluation value of a threshold or higher in the inspection substrate, and receiving light transmitted or reflected from the inspection substrate irradiated by inspection light, thereby adjusting the height position of the pattern forming surface of the inspection substrate to the height position of the pattern forming surface corresponding to the value of the inspection autofocus signal when an optical image of the inspection substrate is captured by a sensor.

[0014] One aspect of the pattern inspection method of the present invention is characterized by using an autofocus signal (used as a parameter for autofocus control) and a focus evaluation value (used for evaluating the focus position) obtained while the evaluation substrate with an evaluation pattern is placed on a worktable, and while the height position of the pattern forming surface of the evaluation substrate is variable, to generate correlation data of the autofocus signal and the focus evaluation value, storing the correlation data in a storage device; using the autofocus signal and the focus evaluation value obtained while the inspection substrate with a graphic pattern is placed on the worktable, and while the height position of the pattern forming surface of the inspection substrate is variable, along with the correlation data of the evaluation substrate, to calculate an inspection autofocus signal that obtains a focus evaluation value of a threshold or higher in the inspection substrate; adjusting the height position of the pattern forming surface of the inspection substrate to a height position corresponding to the value of the inspection autofocus signal; receiving light transmitted or reflected from the inspection substrate irradiated by inspection light; thereby capturing an optical image of the inspection substrate by a sensor; comparing the captured optical pixels with a reference image; and outputting the result.

[0015] Invention Effects According to one aspect of the present invention, the parameters required for the automatic focusing operation of the substrate under inspection can be obtained in a shorter time than before. Attached Figure Description

[0016] Figure 1 This is a structural diagram showing the structure of the pattern inspection device in Embodiment 1.

[0017] Figure 2 This is a conceptual diagram used to illustrate the inspection area in Implementation Method 1.

[0018] Figure 3 This is a diagram showing an example of the measurement results of the amount of light used for autofocus control in the comparative example of Embodiment 1.

[0019] Figure 4 This is a diagram illustrating an example of the autofocus signal in a comparative example of Embodiment 1.

[0020] Figure 5 This is a flowchart illustrating a portion of the main steps of the inspection method in Implementation Method 1.

[0021] Figure 6 This is a flowchart showing the remaining part of one example of the main steps of the inspection method in Implementation Method 1.

[0022] Figure 7 This is a block diagram illustrating an example of the internal structure of the autofocus control circuit in Embodiment 1.

[0023] Figure 8 This is a diagram illustrating an example of the method for calculating contrast in Embodiment 1.

[0024] Figure 9 This is a diagram illustrating another example of the method for calculating contrast in Embodiment 1.

[0025] Figure 10 This is a diagram illustrating an example of the method for calculating brightness in Embodiment 1.

[0026] Figure 11 It is a diagram showing the state of the focus evaluation values ​​of each autofocus signal value of the evaluation substrate in Embodiment 1.

[0027] Figure 12 It is a graph showing the state of the focus evaluation values ​​of each autofocus signal value of the substrate under inspection in Embodiment 1.

[0028] Figure 13 This is a diagram used to illustrate the filtering process in Implementation Method 1.

[0029] Figure 14 This is a diagram illustrating an example of the internal structure of the comparator circuit in Implementation 1. Detailed Implementation

[0030] [Implementation Method 1] Figure 1 This is a structural diagram showing the structure of the pattern inspection device in Embodiment 1. Figure 1 The inspection apparatus 100, which inspects for defects in patterns formed on a substrate such as a mask, includes an optical image acquisition mechanism 150 and a control system circuit 160.

[0031] The optical image acquisition mechanism 150 includes a light source 103, a reflective illumination optical system 171, a movably configured XYθ stage 102, a magnifying optical system 104, a beam splitter 174, a beam splitter 177, a collimating lens 176, an imaging optical system 178, an autofocus mechanism 131, an image sensor 105, a sensor circuit 106, a strip pattern memory 123, a laser length measuring system 122, and an automatic loader 130. When performing transmission inspection using transmitted light, the transmission illumination optical system 170 is also provided. When performing only reflection inspection using reflected light without transmission inspection, the transmission illumination optical system 170 can be omitted. When performing both transmission and reflection inspections simultaneously, an image sensor (not shown) is added, and the image sensor 105 captures images for reflection inspection, while the added image sensor captures images for transmission inspection.

[0032] The autofocus mechanism 131 includes an autofocus optical system 180, a light sensor 185 (first light sensor), a light sensor 187 (second light sensor), a Z-drive mechanism 132, and a position sensor 134.

[0033] The autofocusing optical system 180 includes an imaging optical system 181, a beam splitter 182, a slit plate 184, and a slit plate 186. The autofocusing optical system 180 guides light transmitted or reflected from a substrate to light quantity sensors 185 and 187. The beam splitter 182 is positioned in front of the focal point. The slit plate 184 is positioned at the front focal point and receives light transmitted through the beam splitter 182. The light quantity sensor 185 measures the amount of light passing through the slit plate 184 positioned at the front focal point. The slit plate 186 is positioned at the rear focal point and receives light split by the beam splitter 182. The light quantity sensor 187 measures the amount of light passing through the slit plate 186 positioned at the rear focal point.

[0034] A substrate 101 to be inspected, transported from an automatic loader 130, is disposed on an XYθ stage 102. The substrate 101 to be inspected may include, for example, a photomask for transferring patterns onto a semiconductor substrate such as a wafer. Furthermore, a pattern to be inspected is formed on this photomask. The substrate 101 is disposed on the XYθ stage 102, for example, with the pattern forming surface facing downwards. This is an example of the stage of the XYθ stage 102.

[0035] As the camera sensor 105, a line sensor or a two-dimensional sensor is used. For example, a TDI (Time Delay Integration) sensor is preferred. A TDI sensor has multiple photoelectric sensor elements arranged in a two-dimensional configuration. When each photoelectric sensor element captures an image, a predetermined image accumulation time is set. In the TDI sensor, the outputs of the multiple photoelectric sensor elements arranged along the scanning direction are integrated and output. The multiple photoelectric sensor elements arranged in the scanning direction capture the same pixels while being staggered in time according to the movement of the XYθ stage 102. When using a line sensor, the multiple photoelectric sensor elements are configured to be arranged in a direction orthogonal to the scanning direction.

[0036] In the control system circuit 160, the control computer 110 of the entire control and inspection device 100 is connected via bus 120 to position circuit 107, comparison circuit 108, reference image production circuit 112, automatic loader control circuit 113, worktable control circuit 114, automatic focusing control circuit 140, disk drive 109, memory 111, magnetic tape drive 115, floppy disk drive (FD) 116, CRT 117, pattern monitor 118, and printer 119. Additionally, image sensor 105 is connected to strip pattern memory 123, and strip pattern memory 123 is connected to comparison circuit 108. Furthermore, reference image production circuit 112 is connected to comparison circuit 108.

[0037] The output of position sensor 134 is connected to autofocus control circuit 140. Additionally, the outputs of light sensors 185 and 187 are also connected to autofocus control circuit 140.

[0038] Furthermore, the series of "~circuits" such as position circuit 107, comparison circuit 108, image creation circuit 112, automatic loader control circuit 113, worktable control circuit 114, and automatic focus control circuit 140 have processing circuits. These processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Each circuit can be constructed using the same processing circuit (one processing circuit) or different processing circuits (different processing circuits). For example, the series of "~circuits" such as position circuit 107, comparison circuit 108, image creation circuit 112, automatic loader control circuit 113, worktable control circuit 114, and automatic focus control circuit 140 can also be constructed and executed by control computer 110. The input data or calculation results required by position circuit 107, comparison circuit 108, image creation circuit 112, automatic loader control circuit 113, worktable control circuit 114, and automatic focus control circuit 140 are stored each time in a memory (not shown) or memory 111 within each circuit. The input data or calculation results required to control the computer 110 are stored in a memory (not shown) or memory 111 within the control computer 110 each time. The program that causes the processor to execute can be recorded on a recording medium such as a disk drive 109, magnetic tape drive 115, FD 116, or ROM (read-only memory).

[0039] In the inspection apparatus 100, an inspection optical system 175 is equipped with a reflective inspection optical system and / or a transmissive inspection optical system. A high-magnification reflective inspection optical system is constructed from a light source 103, a reflective illumination optical system 171, a beam splitter 174, a magnifying optical system 104, an XYθ stage 102, a collimating lens 176, and an imaging optical system 178. Alternatively, a high-magnification transmissive inspection optical system is constructed from a light source 103, a transmissive illumination optical system 170, an XYθ stage 102, a magnifying optical system 104, a collimating lens 176, and an imaging optical system 178.

[0040] Furthermore, the XYθ worktable 102 is driven by the worktable control circuit 114 under the control of the control computer 110. It can move using a drive system such as a three-axis (XY-θ) motor that drives along the X, Y, and θ directions. These X, Y, and θ motors can be, for example, stepper motors. The XYθ worktable 102 can move horizontally and in the rotational direction via the motors on each of the X, Y, and θ axes. The XYθ worktable 102 is an example of a worktable. The position of the substrate 101 disposed on the XYθ worktable 102 is measured by the laser length measuring system 122 and supplied to the position circuit 107. Additionally, the transfer of the substrate 101 from the automatic loader 130 to the XYθ worktable 102, and the transfer of the substrate 101 from the XYθ worktable 102 to the automatic loader 130, are controlled by the automatic loader control circuit 113.

[0041] Furthermore, the XYθ stage 102 is driven in the z-direction by a Z-drive mechanism 132 controlled by an autofocus control circuit 140. The Z-drive mechanism 132 is preferably a piezoelectric element or a stepper motor, for example. Additionally, the height position of the XYθ stage 102 is determined by a position sensor 134, and the measurement result is output to the autofocus control circuit 140.

[0042] The drawing data (design data) that forms the basis for the pattern formation of the substrate 101 under inspection is input from outside the inspection device 100 and stored in the disk device 109. Multiple graphic patterns are defined in the drawing data, each typically consisting of a combination of multiple element graphics. Alternatively, a graphic pattern consisting of a single graphic may also be used. On the substrate 101 under inspection, corresponding patterns are formed based on the graphic patterns defined in the drawing data.

[0043] Here, in Figure 1 The document describes the structural components required to explain Embodiment 1. Of course, the inspection device 100 may also typically include other necessary structures.

[0044] Figure 2 This is a conceptual diagram used to illustrate the inspection area in Implementation Method 1. For example... Figure 2As shown, the inspection area 10 (the entire inspection area) of the substrate 101 is virtually divided, for example, into multiple strip-shaped inspection strips 20 in the Y direction, which are elongated strips of scanning width W of the camera sensor 105. Then, in the inspection apparatus 100, an image (strip area image) is acquired for each inspection strip 20. For each inspection strip 20, an image of the graphic pattern arranged within that inspection strip 20 is captured using a laser (inspection light) in the direction of the long side (X direction) of that strip area. Furthermore, to prevent image omission, the multiple inspection strips 20 are preferably arranged such that adjacent inspection strips 20 overlap each other with a predetermined margin width.

[0045] By moving the XYθ stage 102, the camera sensor 105 continuously moves relative to each other along the X direction while acquiring optical images. The camera sensor 105 continuously captures images such as... Figure 2 The optical image with scan width W is shown. In Embodiment 1, after capturing an optical image in one inspection strip 20, the device moves in the Y direction to the position of the next inspection strip 20, and this time, while moving in the opposite direction, optical images with scan width W are captured continuously in the same manner. That is, the images are captured repeatedly in the forward (FWD)-backward (BWD) direction in both the outgoing and return paths.

[0046] In addition, during actual inspections, such as Figure 2 As shown, the strip region image of each inspection strip 20 is divided into multiple rectangular frame regions 30 (frame images 31). Then, each frame image 31 of the frame region 30 is inspected. For example, it is divided into 512×512 pixel dimensions. Therefore, the reference image for comparison with the frame images 31 of the frame region 30 is also made in the same way for each frame region 30.

[0047] Here, the camera direction is not limited to a forward (FWD) - backward (BWD) repeat. It can also be shot from one direction. For example, it can be a repeat of FWD-FWD. Or, it can be a repeat of BWD-BWD.

[0048] As described above, in addition to the inspection optical system 175 (reflective inspection optical system and / or transmission inspection optical system), the inspection device 100 also includes an automatic focusing mechanism 131 for detecting the displacement of the inspection object, i.e., the substrate 101, relative to the inspection optical system 175 in the height direction.

[0049] Here, as patterns become more miniaturized, the wavelength of inspection light continues to shorten. As a result, the focal depth of the inspection optical system 175 becomes shallower. Therefore, the accuracy of a separate measurement system located near the inspection optical system is sufficient. However, without in-situ measurements utilizing the inspection optical system itself, it is impossible to detect the various variations (dependence on temperature / mechanical deformation) inherent in the inspection optical system, and high-precision focal adjustment is not possible.

[0050] That is, in the autofocus mechanism, in addition to the signal output change (sensor output) accompanying the change in mask height, it is also required to detect (monitor) the state changes of the inspection optical system. In order to utilize the inspection optical system with the autofocus optical system, the method of using (dual-wavelength aberration corrected) objective lens adapted to the initial measurement light source (red laser) has been transformed into a method of setting up an optical system that uses DUV light as the inspection light, based on the further high precision requirements of the objective lens.

[0051] Figure 3 This is a diagram showing an example of the measurement results of the light quantity used for autofocus control in the comparative example of Embodiment 1. Figure 3 In the comparative example, the signal variations of the light quantity signal AF-F at the front focal position and the light quantity signal AF-R at the rear focal position are shown relative to the height position of the pattern-forming surface of the mask, measured by a confocal optical system. The light quantity signals AF-F and AF-R ideally represent variations symmetrically about their maximum values. Furthermore, the light quantity signals AF-F and AF-R ideally have the same distribution. Therefore, the light quantity signals AF-F and AF-R ideally vary symmetrically with respect to the focal position. In this case, the value obtained by dividing the difference between the light quantity signals AF-F and AF-R by the sum (autofocus signal: AF signal) varies linearly with respect to the height position of the pattern-forming surface of the mask.

[0052] Therefore, by varying the height of the mask's pattern-forming surface, the autofocus signal and the contrast of the resulting image are calculated at each height. Then, a correlation curve is created between the autofocus signal and the image contrast, and the autofocus signal with the highest contrast is calculated as the autofocus signal for the focal position. In the autofocus mechanism, the feedback autofocus signal serves as the stage displacement signal, and the stage height is adjusted to ensure that the autofocus signal becomes the autofocus signal for the focal position.

[0053] However, the light reaching the slit plates 184 and 186 exhibits different distribution variations when the height of the mask's pattern-forming surface changes due to astigmatism caused by performance deviations of optical elements and optical adjustment deviations. As a result, there are cases where the change in the light quantity signal measured by the light quantity sensors 185 and 187 relative to the mask's height position through the slit plates 184 and 186 is not symmetrically bounded by a maximum value. Figure 3 In the comparative example, a shift occurs when the light quantity signal AF-R at the rear focal position is reversed and overlaps with the light quantity signal AF-F at the front focal position. Thus, the light quantity signals AF-F and AF-R change asymmetrically relative to the focal position.

[0054] Figure 4 This is a diagram illustrating an example of the autofocus signal in a comparative example of Embodiment 1. The autofocus signal can be defined by dividing the difference between the light intensity signal AF-F and the light intensity signal AF-R by the sum. If the light intensity signals AF-F and AF-R vary symmetrically around their maximum values ​​and have the same distribution, then the autofocus signal is proportional to the change in the height position of the mask pattern forming surface. However, as... Figure 4 As shown in the comparative example, the autofocus signal changes nonlinearly and disproportionately with respect to the height position of the mask's pattern-forming surface. Therefore, the change in the autofocus signal's height position relative to the mask's pattern-forming surface generates a nonlinear error.

[0055] Therefore, the correlation curve between the autofocus signal and the image contrast becomes an asymmetrical curve. This correlation curve is calculated for each inspected substrate, and the autofocus signal with the highest contrast in this curve is the inspection autofocus signal for that substrate. However, due to the complex asymmetrical curve, the approximation error increases when the number of measurement points is small. Therefore, a high-precision inspection autofocus signal cannot be obtained with a small number of measurement points. On the other hand, when measuring each inspected substrate with a large number of measurement points, the process for obtaining the inspection autofocus signal is time-consuming. To shorten the inspection time and thus increase throughput, it is necessary to shorten the time spent on the process for obtaining the inspection autofocus signal with higher image contrast.

[0056] Therefore, in Embodiment 1, instead of using the substrate under inspection to obtain the high-precision correlation curve, the correlation curve is obtained in advance, for example, during the manufacturing and assembly of the inspection apparatus 100 using an evaluation substrate. Then, during actual inspection, the autofocus signal for inspection of the substrate under inspection is calculated by making the correlation curve obtained from the evaluation substrate match the result of fewer measurement points obtained from the substrate under inspection. This will be explained in detail below.

[0057] Figure 5 This is a flowchart illustrating a portion of the main steps of the inspection method in Implementation Method 1.

[0058] Figure 6 This is a flowchart showing the remaining part of one example of the main steps of the inspection method in Implementation Method 1.

[0059] exist Figure 5 and Figure 6 In Implementation Method 1, the inspection method performs the following series of steps: evaluation substrate loading process (S102), evaluation substrate height position setting and measurement process (S104), light intensity measurement process (S106), autofocus signal calculation process (S108), optical image acquisition process (S110), focus evaluation value calculation process (S112), related data production process (S120), inspection substrate loading process (S202), inspection substrate height position setting and measurement process (S204), light intensity measurement process (S206), autofocus signal calculation process (S208), optical image acquisition process (S210), focus evaluation value calculation process (S212), measurement value plotting process (S220), inspection autofocus signal calculation process (S222), image acquisition (autofocus control) process (S250), and comparison process (S252).

[0060] The relevant data production process (S120) includes the measurement value plotting process (S122) and the function approximation process (S124) as internal processes.

[0061] As part of the evaluation substrate handling process (S102), the evaluation substrate transported from the automatic loader 130 is placed on the XYθ worktable 102.

[0062] Figure 7 This is a block diagram illustrating an example of the internal structure of the autofocus control circuit in Embodiment 1. Figure 7 The autofocus control circuit 140 includes storage devices such as disk drives 51, 57, and 61; an autofocus signal calculation unit 50; an evaluation value calculation unit 52; a related data production unit 53; a table height control unit 62; an autofocus signal calculation unit 64; an autofocus processing unit 66; an autofocus signal calculation unit 80; an evaluation value calculation unit 82; a plotting processing unit 84; an inspection autofocus signal calculation unit 86; and an offset calculation unit 88.

[0063] A plotting processing unit 54 and a fitting processing unit 56 are configured within the relevant data production unit 53.

[0064] The series of units including the autofocus signal calculation unit 50, evaluation value calculation unit 52, correlation data generation unit 53 (plotting processing unit 54 and fitting processing unit 56), stage height control unit 62, autofocus signal calculation unit 64, autofocus processing unit 66, autofocus signal calculation unit 80, evaluation value calculation unit 82, plotting processing unit 84, inspection autofocus signal calculation unit 86, and offset calculation unit 88, all have processing circuitry. This processing circuitry includes electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Alternatively, each unit may use a common processing circuit (the same processing circuit), or different processing circuits may be used (different processing circuits). The input data or calculated results required by the autofocus signal calculation unit 50, evaluation value calculation unit 52, related data production unit 53 (plotting processing unit 54 and fitting processing unit 56), worktable height control unit 62, autofocus signal calculation unit 64, autofocus processing unit 66, autofocus signal calculation unit 80, evaluation value calculation unit 82, plotting processing unit 84, inspection autofocus signal calculation unit 86 and offset calculation unit 88 are stored each time in a memory (not shown) or memory 111 within the autofocus control circuit 140.

[0065] As part of the evaluation substrate height position setting and measurement process (S104), under the control of the stage height control unit 62, the height position of the XYθ stage 102 is driven by the Z drive mechanism 132, thereby variably setting the evaluation substrate height position (pattern forming surface height position). Furthermore, the evaluation substrate height position is measured by the position sensor 134. The evaluation substrate height position h measured by the position sensor 134 is output to the autofocus control circuit 140 and stored in the storage device 61.

[0066] Evaluation patterns are formed on the evaluation substrate. For example, line and space patterns can be used as evaluation patterns. For instance, a 1:1 line and space pattern can be used. Alternatively, a hole pattern with a specified pattern density (e.g., 50%) can be used. The linewidth d of these evaluation patterns can be defined by the light source wavelength λ of the inspection apparatus 100 and the numerical aperture NA of the optical system, using the following formula (1). k is preferably set to a value greater than 1. For example, it is preferably set to a value in the range of 1 < k < 10.

[0067] (1)λ / (2NA)≤d≤k(λ / (2NA)) As part of the light intensity measurement step (S106), with the evaluation substrate height position controlled at height position hi, the light intensity at the front focal position of the light transmitted or reflected from the evaluation substrate illuminated by the inspection light is measured using the light intensity sensor 185. Similarly, the light intensity at the rear focal position is measured using the light intensity sensor 187. Specifically, the operation is performed as follows. (i denotes an index.)

[0068] A laser beam (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 via a reflective illumination optical system 171 and directed towards a beam splitter 174 to become the inspection light. The irradiated laser beam is reflected by the beam splitter 174 and then illuminates the evaluation substrate via a magnifying optical system 104. The light reflected from the evaluation substrate passes through the magnifying optical system 104 and the beam splitter 174, illuminating the beam splitter 177. The light branched by the beam splitter 177 then enters the autofocus optical system 180.

[0069] Light incident on the autofocus optical system 180 is refracted in a focusing direction by the imaging optical system 181 and illuminates the beam splitter 182. A portion of the light transmitted through the beam splitter 182 is confined by a slit plate 184 at the front focal position, and the amount of light passing through the slit plate 184 is measured by the light quantity sensor 185. A portion of the light split by the beam splitter 182 is confined by a slit plate 186 at the rear focal position, and the amount of light passing through the slit plate 186 is measured by the light quantity sensor 187. Thus, it is possible to measure the amount of light at the front focal position and the amount of light at the rear focal position at a height position hi. The measured light quantity data (light intensity data) at the front focal position and the rear focal position at a height position hi is stored in the storage device 51.

[0070] As part of the autofocus signal calculation process (S108), the autofocus signal calculation unit 50 calculates the autofocus signal εi, which is used as a parameter for autofocus control when the substrate height position is height position hi. The autofocus signal εi is defined by the following formula (2) using the light quantity Ai at the front focal position and the light quantity Bi at the rear focal position. i represents the index.

[0071] (2) εi=(Ai-Bi) / (Ai+Bi) The value of the autofocus signal εi is stored in, for example, a storage device 51 in association with the height position hi.

[0072] As part of the optical image acquisition process (S110), the optical image acquisition mechanism 150, with the evaluation substrate placed on the XYθ stage 102, receives light transmitted or reflected from the evaluation substrate by the camera sensor 105 via the inspection optical system 175 at a set height position hi, thereby capturing an optical image of the evaluation substrate. Specifically, the operation is performed as follows.

[0073] The optical image acquisition mechanism 150 scans the inspection strip 20 of the evaluation substrate, which includes a pre-defined frame region 30, using a laser (inspection light), and captures an image of the strip region using an image sensor 105. Specifically, the operation is as follows: The XYθ stage 102 is moved to a position where the inspection strip 20, which is the object of the evaluation substrate, can be captured. In transmission inspection, a laser (e.g., DUV light) of a wavelength below the ultraviolet region, which becomes the inspection light, is irradiated from a suitable light source 103 via a transmission illumination optical system 170 onto the pattern formed on the evaluation substrate. In other words, the transmission illumination optical system 170 illuminates the patterned evaluation substrate. The light transmitted through the evaluation substrate is imaged as an optical image on the image sensor 105 (an example of a sensor) by means of an imaging optical system 178 via a magnifying optical system 104 and a collimating lens 176.

[0074] Alternatively, in reflective inspection, for a pattern formed on an evaluation substrate, a laser (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 towards a beam splitter 174 via a reflective illumination optical system 171. The irradiated laser is reflected by the beam splitter 174 and irradiates the evaluation substrate via a magnifying optical system 104. The light reflected from the evaluation substrate passes through the magnifying optical system 104, the beam splitter 174, and the collimating lens 176, and is imaged onto the camera sensor 105 as an optical image via an imaging optical system 178.

[0075] The camera sensor 105 captures optical images of the evaluation substrate.

[0076] The image of the pattern imaged on the camera sensor 105 is converted into an image by the photoelectric sensor elements of the camera sensor 105 and then converted into an analog-to-digital (A / D) image by the sensor circuit 106. Furthermore, the pixel values ​​of the test strip 20 of the test object are stored in the strip pattern memory 123. The test data (pixel data) is, for example, 8-bit unsigned data representing the grayscale (light intensity) of each pixel's brightness. Then, the frame image 31 (test image) of the pre-set frame region 30 in the test strip image is output to the autofocus control circuit 140 and stored in the storage device 61.

[0077] As part of the focus evaluation value calculation process (S112), the evaluation value calculation unit 52 calculates a focus evaluation value based on the obtained image. For example, the focus evaluation value may be one of contrast and brightness obtained from the optical image.

[0078] Figure 8 This is a diagram illustrating an example of the method for calculating contrast in Embodiment 1. Figure 8In the example shown, a line and spatial pattern that serves as an evaluation pattern is presented in the measurement image. In this case, the contrast of the grayscale data of each of the multiple lines in the direction (x direction) orthogonal to the direction (y direction) of the extension of the line pattern (or spatial pattern) is calculated. The contrast C can be defined using the maximum and minimum values ​​of the grayscale data, as shown in the following equation (3).

[0079] (3) C = (maximum value - minimum value) / (maximum value + minimum value) Then, as the contrast of the image, the average contrast of all lines is calculated, for example. Additionally, to mitigate measurement bias, it is preferable to use the average contrast of as many lines as possible, but not limited to all lines.

[0080] Figure 9 This is a diagram illustrating another example of the method for calculating contrast in Embodiment 1. Figure 9 In the example shown, a hole pattern is presented in the measurement image as another example of an evaluation pattern. In this case, the contrast of grayscale data of each line in a direction orthogonal to the y direction, such as the x direction, is calculated at multiple locations overlapping the hole pattern, for example in the y direction. The contrast C can be defined using the maximum and minimum values ​​of the grayscale data, as defined by equation (3) above.

[0081] Then, the contrast of the image on the evaluation substrate is used as an example to calculate the average contrast of all lines.

[0082] Figure 10 This is a diagram illustrating an example of the method for calculating brightness in Embodiment 1. Figure 10 The example shown illustrates a histogram where the vertical axis represents the number of pixels (degrees) and the horizontal axis represents grayscale values. This histogram is created using measurements of all pixels within the image. The total number of pixels representing grayscale values ​​above a threshold Th is then defined as the image's brightness.

[0083] Then, returning to the evaluation substrate height position setting and measurement step (S104), the process from the evaluation substrate height position setting and measurement step (S104) to the focus evaluation value calculation step (S112) is repeated while changing the evaluation substrate height position. This allows the height position of the pattern forming surface of the evaluation substrate to be variable, and an optical image of the evaluation substrate is acquired at each height position. Furthermore, an AF signal is acquired at each height position. Then, the evaluation value calculation unit 52 calculates a focus evaluation value for evaluating the focus position at each height position while allowing the height position of the pattern forming surface of the evaluation substrate with the pattern to be variable. AF signals and focus evaluation values ​​are acquired at height positions of 4 points or higher. More preferably, AF signals and focus evaluation values ​​are acquired at height positions of 10 points or higher. Preferably.

[0084] As part of the related data production process (S120), the related data production unit 53 uses an autofocus signal (AF signal) for each height position, which is used as a parameter for autofocus control, and a focus evaluation value for evaluating the focus position, obtained while the evaluation substrate with the evaluation pattern formed on the XYθ stage 102 (stage) is placed on the stage, and the height position of the pattern forming surface of the evaluation substrate is variable, to produce related data of the AF signal and the focus evaluation value. This will be explained in detail below.

[0085] As part of the measurement value plotting process (S122), the plotting processing unit 54 plots the obtained AF signal values ​​in a coordinate system where the vertical axis represents the focus evaluation value and the horizontal axis represents the AF signal.

[0086] Figure 11 This is a diagram showing the state of the focus evaluation values, plotted with the autofocus signal values ​​of the evaluation substrate in Embodiment 1. Figure 11 In the diagram, the vertical axis represents the focus evaluation value, and the horizontal axis represents the autofocus signal value. Figure 11 The example shows the focus evaluation values ​​for the autofocus signal values ​​ε1, εi, and εN at 6 points. Because an autofocus signal is used, the graph is not symmetrical, resulting in nonlinear errors.

[0087] As a function approximation step (S124), the fitting processing unit 56 approximates the focus evaluation value of each plotted autofocus signal value using a convex polynomial function. For example... Figure 11 As shown in the example, a function with a maximum focus evaluation value Cm when the AF signal value is εm, obtained by approximating the AF signal and focus evaluation value at each height position, is used as the relevant data.

[0088] The examples above illustrate the use of approximate functions as correlation data, but are not limited to this. For instance, as correlation data, it is preferable to use a numerical column of AF signals and focus evaluation values ​​for each altitude position.

[0089] The obtained relevant data is stored in storage device 57. The curve shape obtained from the relevant data of the evaluation substrate is used as a template on the substrate to be inspected.

[0090] As part of the substrate loading process (S202), the substrate 101 to be inspected, which is being transported from the automatic loader 130, is placed on the XYθ worktable 102.

[0091] As part of the substrate height setting and measurement process (S204), the height position of the XYθ stage 102 is driven by the Z-drive mechanism 132 under the control of the stage height control unit 62, thereby variably setting the substrate height position (pattern forming surface height position). The substrate height position is also measured by the position sensor 134. The substrate height position h measured by the position sensor 134 is output to the autofocus control circuit 140 and stored in the storage device 61.

[0092] A graphic pattern of the object to be inspected is formed on the substrate 101 to be inspected. For example, line and space patterns, hole patterns are formed.

[0093] As part of the light intensity measurement step (S206), with the height position of the substrate to be inspected controlled at height position hj, the light intensity at the front focal point of the light transmitted or reflected from the substrate 101 illuminated by the inspection light is measured using the light intensity sensor 185. Similarly, the light intensity at the rear focal point is measured using the light intensity sensor 187. Specifically, the operation is performed as follows. j denotes an index.

[0094] A laser beam (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 via a reflective illumination optical system 171 and directed towards a beam splitter 174 to become the inspection light. The irradiated laser beam is reflected by the beam splitter 174 and then passes through a magnifying optical system 104 to illuminate the substrate 101 under inspection. The light reflected from the substrate 101 under inspection passes through the magnifying optical system 104 and the beam splitter 174, illuminating the beam splitter 177. The light branched by the beam splitter 177 then enters the autofocusing optical system 180.

[0095] Light incident on the autofocus optical system 180 is refracted in a focusing direction by the imaging optical system 181 and illuminates the beam splitter 182. A portion of the light transmitted through the beam splitter 182 is confined by a slit plate 184 at the front focal position, and the amount of light passing through the slit plate 184 is measured by the light quantity sensor 185. A portion of the light split by the beam splitter 182 is confined by a slit plate 186 at the rear focal position, and the amount of light passing through the slit plate 186 is measured by the light quantity sensor 187. Thus, it is possible to measure the amount of light at the front focal position and the amount of light at the rear focal position at the height position hj. The measured light quantity data (light intensity data) at the front focal position and the rear focal position at the height position hj are stored in the storage device 51.

[0096] As part of the autofocus signal calculation process (S208), the autofocus signal calculation unit 80 calculates the AF signal δj at the height position hj of the substrate being inspected. The AF signal δj is defined by equation (4) using the light quantity Aj at the front focal position and the light quantity Bj at the rear focal position. j represents the index.

[0097] (4) δj=(Aj-Bj) / (Aj+Bj) The value of the AF signal δj, for example, is stored in the storage device 51 in association with the altitude position hj.

[0098] As part of the optical image acquisition process (S210), the optical image acquisition mechanism 150, with the substrate 101 to be inspected placed on the XYθ stage 102, receives light transmitted or reflected from the substrate 101 illuminated by the inspection light via the camera sensor 105 at a set height position hj, thereby capturing an optical image of the substrate 101 to be inspected.

[0099] The optical image acquisition mechanism 150 scans the inspection strip 20 of the substrate 101 to be inspected, which includes a pre-defined frame region 30, using a laser (inspection light), and captures an image of the strip region using an image sensor 105. Specifically, the operation is performed as follows: The XYθ stage 102 is moved to a position where the inspection strip 20, which is the object of the substrate 101 to be inspected, can be captured. In transmission inspection, a laser (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 onto the pattern formed on the substrate 101 to be inspected via a transmission illumination optical system 170. In other words, the transmission illumination optical system 170 illuminates the patterned substrate to be inspected. The light transmitted through the substrate 101 to be inspected is imaged as an optical image on the image sensor 105 (an example of a sensor) via a magnifying optical system 104 and a collimating lens 176, and then incident on the image sensor 105 (an example of a sensor) via an imaging optical system 178.

[0100] Alternatively, in reflective inspection, for the pattern formed on the substrate 101 under inspection, a laser (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 through a reflective illumination optical system 171 onto a beam splitter 174 to become the inspection light. The irradiated laser is reflected by the beam splitter 174 and then irradiates the substrate 101 under inspection through a magnifying optical system 104. The light reflected from the substrate 101 under inspection passes through the magnifying optical system 104, the beam splitter 174, and the collimating lens 176, and is imaged onto the camera sensor 105 by the imaging optical system 178 to form an optical image, which is then incident on the sensor.

[0101] The camera sensor 105 captures an optical image of the substrate 101 being inspected.

[0102] The image of the pattern imaged on the camera sensor 105 is converted into an image by the photoelectric sensor elements of the camera sensor 105 and then converted into an analog-to-digital (A / D) image by the sensor circuit 106. Furthermore, the pixel values ​​of the test strip 20 of the test object are stored in the strip pattern memory 123. The test data (pixel data) is, for example, 8-bit unsigned data representing the grayscale (light intensity) of each pixel's brightness. Then, the frame image 31 (test image) of the pre-set frame region 30 in the test strip image is output to the autofocus control circuit 140 and stored in the storage device 61.

[0103] As part of the focus evaluation value calculation process (S212), the evaluation value calculation unit 82 calculates a focus evaluation value based on the obtained image. The focus evaluation value may be, for example, either contrast or brightness obtained from the optical image. Here, the same value as the focus evaluation value of the evaluation substrate is used. For example, contrast is used. In the substrate 101 being inspected, the same value is used... Figure 8 Similarly, as described above, the contrast of the grayscale data of each of the multiple lines in the direction orthogonal to the direction (y-direction) of the extension of the line pattern (or spatial pattern) is calculated. The contrast C can be defined using the maximum and minimum values ​​of the grayscale data, as given by equation (3).

[0104] Then, as a measure of the contrast of the image of the substrate 101 under inspection, the average contrast of all lines is calculated, for example. Furthermore, to mitigate measurement bias, the average contrast of as many lines as possible is preferred, but not limited to all lines. The pattern used to calculate the average contrast can, for example, be a pattern of a size that matches the performance of the inspection apparatus 100 and is close to the evaluation pattern of the evaluation substrate.

[0105] Or / and, in cases where the measured image presents a hole pattern that is another example of the pattern being examined, with Figure 9 Similarly, the contrast of grayscale data for each line in a direction orthogonal to the y-direction, such as the x-direction, at multiple locations overlapping the hole pattern, for example, in the y-direction, is calculated. The contrast ratio C can be calculated using the maximum and minimum values ​​of the grayscale data, as defined by equation (3) above.

[0106] Then, as the contrast of the image of the substrate 101 under inspection, for example, the average contrast of all lines is calculated. The method for calculating brightness is as follows: Figure 10 As explained in the text.

[0107] Then, returning to the substrate height position setting and measurement process (S204), the process from substrate height position setting and measurement process (S204) to focus evaluation value calculation process (S212) is repeated while changing the substrate height position. Thus, while making the height position of the pattern forming surface of the substrate 101 variable, an optical image of the substrate 101 is acquired for each height position. Furthermore, an AF signal is acquired for each height position. Then, the evaluation value calculation unit 82 calculates a focus evaluation value for evaluating the focus position for each height position while making the height position of the pattern forming surface of the evaluation substrate with the patterned shape variable. Here, the AF signal and focus evaluation value of the substrate 101 at each height position hj are acquired at at least three different height positions hj, fewer than when acquiring the relevant data of the evaluation substrate.

[0108] As part of the measurement value plotting process (S220), the plotting processing unit 84 plots the obtained AF signal values ​​in a coordinate system where the vertical axis represents the focus evaluation value and the horizontal axis represents the AF signal.

[0109] Figure 12 This is a graph showing the state of the focus evaluation values ​​of each autofocus signal value of the substrate under inspection in Embodiment 1. Figure 12 In the diagram, the vertical axis represents the focus evaluation value, and the horizontal axis represents the autofocus signal value. Figure 12 In the example, δj represents the focus evaluation value at the autofocus signal value of point 3.

[0110] Here, the AF signal value representing the height of the substrate under inspection changes with the temperature of the device, or the contrast evaluation value is affected by changes in the phase of the substrate under inspection, etc. Therefore, the combined value of the AF signal and focus evaluation value obtained in the substrate under inspection 101 may not be consistent with the combined value of the AF signal and focus evaluation value in the evaluation substrate. However, the line width of the pattern of the object to be inspected formed on the substrate under inspection 101 is generally formed with dimensions that correspond to the performance of the inspection device 100. Therefore, an action similar to the evaluation pattern is shown.

[0111] As part of the inspection autofocus signal calculation process (S222), the inspection autofocus signal calculation unit 86 uses the AF signal and focus evaluation value obtained at each height position while the inspected substrate 101 with a patterned surface is placed on the XYθ stage 102 (stage), and the height position of the patterned surface of the inspected substrate 101 is variable, as well as relevant data of the evaluation substrate, to calculate the inspection AF signal δm that obtains a focus evaluation value of a threshold or higher in the inspected substrate 101. Specific details will be provided.

[0112] The inspection unit 86 plots multiple combinations of AF signals and focus evaluation values ​​obtained from the inspected substrate 101 to create a graph. Then, as... Figure 12 As shown, the result is that the shape (template) of the curve represented by the relevant data is applied to the plotted substrate 101 under inspection. The template representing the relevant data is applied to the curve of multiple combinations of AF signals and focus evaluation values ​​obtained in the plotted substrate 101 under inspection, so that the multiple combinations are located on the curve represented by the relevant data.

[0113] Then, the autofocus signal calculation unit 86 checks the AF signal δm calculated by the inspection unit for a focus evaluation value of threshold Thf or higher in the curve of the applied template. Threshold Thf is preferably set to, for example, 90% or higher of the maximum value Cm′ of the applied template. More preferably, the autofocus signal calculation unit 86 calculates the AF signal δm that corresponds to the maximum value Cm′ of the applied template. In other words, the autofocus signal calculation unit 86 calculates the AF signal δm corresponding to the maximum value Cm′ of the applied template. Thus, the inspection AF signal δm on the substrate 101 under inspection can be determined. The value of the inspection AF signal δm is stored, for example, in the storage device 51.

[0114] As part of the image acquisition (autofocus control) process (S250), the optical image acquisition mechanism 150 adjusts the height position of the patterned surface of the substrate 101 to correspond to the height position of the patterned surface corresponding to the value of the inspection autofocus signal δm, and receives light transmitted or reflected from the substrate 101 illuminated by the inspection light via the inspection optical system 175 through the camera sensor 105, thereby capturing an optical image of the substrate 101. Specifically, it operates as follows.

[0115] The optical image acquisition mechanism 150 scans the inspection strips 20 of the substrate 101 to be inspected using a laser (inspection light), and captures an image of the strip area for each inspection strip 20 using an image sensor 105. Specifically, the operation is as follows: The XYθ stage 102 is moved to a position where the inspection strip 20 to be inspected can be captured. In transmission inspection, a laser (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 onto the pattern formed on the substrate 101 via a transmission illumination optical system 170. In other words, the transmission illumination optical system 170 illuminates the patterned substrate 101 to be inspected. The light transmitted through the substrate 101 to be inspected is imaged as an optical image on the image sensor 105 (an example of a sensor) by means of an imaging optical system 178 via a magnifying optical system 104 and a collimating lens 176.

[0116] Alternatively, in reflective inspection, for the pattern formed on the substrate 101 under inspection, a laser (e.g., DUV light) of a wavelength below the ultraviolet region is irradiated from a suitable light source 103 towards a beam splitter 174 via a reflective illumination optical system 171 to become the inspection light. The irradiated laser is reflected by the beam splitter 174 and irradiates the sample 101 via a magnifying optical system 104. The light reflected from the sample 101 passes through the magnifying optical system 104, the beam splitter 174, and the collimating lens 176, and is imaged onto the camera sensor 105 as an optical image via an imaging optical system 178.

[0117] When capturing the optical image, the autofocus mechanism 131 adjusts the height position of the pattern forming surface of the substrate 101 under inspection to the height position hm of the pattern forming surface corresponding to the value δm of the inspection AF signal. In other words, with the substrate 101 under inspection placed on the XYθ stage 102, the autofocus mechanism 131 adjusts the height position of the pattern forming surface of the substrate 101 under inspection, which may change with the horizontal movement of the XYθ stage 102, to the height position hm corresponding to the inspection autofocus signal δm. Specifically, the autofocus processing unit 66 inputs the light quantity at the front focal position and the light quantity at the rear focal position from the light quantity sensors 185 and 187, and calculates the AF signal z. Then, it controls the Z-drive mechanism 132 to change the AF signal z to δm.

[0118] Alternatively, offset control can be used. In this case, the offset calculation unit 88 calculates the difference between the inspection AF signal δm and zero as the offset value z0. Then, the autofocus processing unit 66 receives the light quantity at the front focal position and the light quantity at the rear focal position from the light quantity sensors 185 and 187, and calculates the AF signal z. Then, the autofocus processing unit 66 outputs the value obtained by subtracting the offset value z0 from the calculated AF signal z to the Z-drive mechanism 132. In the Z-drive mechanism 132, the mask surface height position is adjusted so that the value obtained by subtracting the offset value z0 from the calculated AF signal z becomes zero.

[0119] When the height position of the pattern forming surface of the substrate 101 under inspection is adjusted to the height position of the pattern forming surface corresponding to the value of the inspection AF signal δm, the camera sensor 105 receives light transmitted or reflected from the substrate 101 under inspection by the inspection light, thereby capturing an optical image of the substrate 101 under inspection.

[0120] The image of the pattern projected onto the camera sensor 105 is converted into an image by the photoelectric sensor elements of the camera sensor 105 and then converted into an analog-to-digital converter by the sensor circuit 106. Furthermore, the pixel values ​​of the inspection strip 20 of the measured object are stored in the strip pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, representing the grayscale (light intensity) of the brightness of each pixel.

[0121] On the other hand, the image creation circuit 112 uses graphic pattern data (design data) to create a reference image. The creation of the reference image is performed in parallel with the scanning operation of each inspection strip 20 of the substrate 101 being inspected. Specifically, the operation is performed as follows: The image creation circuit 112 inputs graphic pattern data (design data) for each frame region 30 of the inspection strip 20 to be inspected, and transforms each graphic pattern defined in the graphic pattern data into binary or multi-valued image data.

[0122] The graphic pattern data defines a graphic as a basic shape, such as a rectangle or triangle. For example, the data stores graphic data that uses information such as the coordinates (x, y) of the graphic's reference position, the length of the side, and the graphic code as an identifier to distinguish between different types of graphics, such as rectangles or triangles, to define the shape, size, position, etc. of each graphic pattern.

[0123] When the design pattern data, which becomes the graphic data, is input to the reference image fabrication circuit 112, it is expanded to the data of each graphic, and the graphic code representing the graphic shape, graphic size, etc., of the graphic data are interpreted. Then, as a pattern arranged within a grid with a specified quantization size, it is expanded into binary or multi-valued design pattern image data and output. In other words, design data is read in, and for each grid obtained by virtually dividing the frame area into grids with a specified size, the occupancy rate of the graphic in the design pattern is calculated, and n bits of occupancy rate data (design image data) are output. For example, it is preferable to set one grid as one pixel. Moreover, if one pixel has 1 / 2 8 For a resolution of (1 / 256), a small region of 1 / 256 of the area of ​​the graphic within a pixel is allocated to calculate the occupancy within that pixel. Then, 8 bits of occupancy data are created. This grid (checking pixels) should match the pixels in the measurement data.

[0124] Next, referring to the image fabrication circuit 112, a filtering function is used to perform filtering processing on the design image data of the design pattern, which is the graphic image data.

[0125] Figure 13This diagram illustrates the filtering process in Embodiment 1. The pixel data of the optical image captured from the substrate 101 being inspected is in a state where the filter is active, depending on the resolution characteristics of the optical system used for capture, etc. In other words, it is in a continuously changing analog state, therefore, for example... Figure 13 As shown, the image intensity (darkness value) differs from the unfolded image (design image) with digital values. On the other hand, in graphic pattern data, as described above, it is defined by graphic codes, etc., so the image intensity (darkness value) may be a digital value in the unfolded design image. Therefore, the image processing circuit 112 performs image processing (filtering) on ​​the unfolded image to generate a reference image that approximates an optical image. Thus, it is possible to make the image generation characteristics of the design image data (design image data) with digital image intensity (darkness value) consistent with those of the measurement data (optical image). The generated reference image is output to the comparison circuit 108.

[0126] Figure 14 This is a diagram illustrating an example of the internal structure of the comparator circuit in Embodiment 1. Figure 14 Within the comparison circuit 108, storage devices such as disk drives 70, 72, and 76, a frame image creation unit 74, a alignment unit 78, and a comparison processing unit 79 are arranged. Each of these "~units" (frame image creation unit 74, alignment unit 78, and comparison processing unit 79) has processing circuitry. This processing circuitry may include electrical circuits, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Alternatively, each "~unit" may use a common processing circuit (the same processing circuit), or different processing circuits (different processing circuits). The input data required by the frame image creation unit 74, alignment unit 78, and comparison processing unit 79, or the results of their calculations, are stored each time in a memory (not shown) or a memory 111 within the comparison circuit 108.

[0127] The strip data (strip region image) input to the comparison circuit 108 is stored in the storage device 70. The reference image data input to the comparison circuit 108 is stored in the storage device 72.

[0128] The comparison process (S252) and the comparison circuit 108 (an example of the comparison unit) compare the captured optical pixels with the reference image using the reference image and output the result. Specifically, it operates as follows.

[0129] In the comparison circuit 108, firstly, the frame image generation unit 74 generates multiple frame images 31, which are formed by dividing the striped region image (optical image) by a predetermined width. Specifically, as... Figure 2As shown, the striped region image is divided into multiple rectangular frame regions 30. For example, it is divided into 512×512 pixel sizes. The data of each frame region 30 is stored in the storage device 76.

[0130] Next, the alignment unit 78 reads the corresponding frame image 31 and the corresponding reference image from the storage devices 72 and 76 for each frame region 30, and performs alignment of the frame image 31 and the corresponding reference image using a predetermined algorithm. For example, alignment is performed using the least squares method.

[0131] Then, the comparison processing unit 79 (another example of a comparison unit) compares the frame image 31 with the reference image corresponding to the frame image 31. For example, the comparison is performed for each pixel. Here, the two are compared for each pixel according to a predetermined determination condition, such as determining whether there is a defect like a shape defect. As a determination condition, the two are compared for each pixel according to a predetermined algorithm to determine whether there is a defect. For example, the difference between the pixel values ​​of the two images is calculated for each pixel, and a defect is determined if the difference value is greater than a threshold Th. The comparison result can be output to, for example, a disk drive 109, a magnetic tape drive 115, a floppy disk drive (FD) 116, a CRT 117, a pattern monitor 118, or a printer 119.

[0132] The above example illustrates a die-to-database check, but a die-to-die check is also possible. In this case, the comparison circuit 108 uses the frame image (optical image) of the die 2 obtained for one of the frame regions 30 undergoing die-to-die checking as a reference (reference image) for each of the multiple frame regions 30. First, the alignment unit 78 reads the corresponding frame image 31 of the die 1 and the frame image of the die 2 from the storage device 76 for each frame region 30 undergoing die-to-die checking, and aligns the frame images 31 of the die 1 and the frame images of the die 2 using a predetermined algorithm. For example, the least squares method is used for alignment. Then, the comparison processing unit 79 (comparison unit) compares the corresponding frame image 31 of the die 1 and the frame image of the die 2 for each pixel for each frame region 30 undergoing die-to-die checking.

[0133] As described above, according to Embodiment 1, the parameters required for the automatic focusing operation of the substrate 101 under inspection can be obtained in a shorter time than before.

[0134] Previously, in order to accurately calculate the AF signal with the largest focus evaluation value, it was necessary to perform "focus evaluation value changes relative to changes in the AF signal" (more than 10 points) at multiple sampling points. On the other hand, according to Implementation Method 1, a method was used... Figure 11The template fabrication process for the evaluation substrate described herein only needs to be performed once when the device is started (excluding inspection time), thus enabling precise acquisition of the template curve based on the collection of multiple sample points (10 points or more, with no time limit). When inspecting the substrate under inspection, as a minimum requirement, for example, 3 sample points can be collected and applied to the template. Therefore, according to Embodiment 1, the time required for the process of obtaining the parameters required for the autofocus operation can be reduced to, for example, 3 / 10 = 30%. This can be further reduced depending on the number of measurement points.

[0135] The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.

[0136] Furthermore, details regarding the device structure, control method, and other aspects not directly required in the description of this invention have been omitted, but the appropriate device structure and control method can be selected for use. For example, the control unit structure of the control inspection device 100 has been omitted, but of course, the appropriate control unit structure can be selected for use.

[0137] Furthermore, all pattern inspection devices, focus position adjustment methods, and pattern inspection methods that incorporate the elements of this invention and can be appropriately modified by those skilled in the art are included within the scope of this invention.

[0138] Industrial availability One aspect of the present invention relates to a pattern inspection apparatus, a focus position adjustment method, and a pattern inspection method. For example, it provides an apparatus capable of inspecting pattern defects in exposure masks used in semiconductor manufacturing, and a focus position adjustment method for that apparatus.

[0139] Explanation of reference numerals in the attached figures 20 Inspection Strips 30 frames area 31 frames of images 50 Autofocus Signal Calculation Unit Storage devices 51, 57, and 61 52 Evaluation Value Calculation Department 53 Related Data Production Department 54 Plotting Department 56 Fitting Processing Unit 62 Workbench Height Control Department 64 Autofocus Signal Calculation Unit 66 Autofocus Processing Unit Storage devices 70, 71, 72, and 76 74-frame image generation unit 78 Opposite Part 79 Comparison Processing Department 80 Autofocus Signal Calculation Unit 82 Evaluation Value Calculation Department 84 Plotting Department 86 Inspection Autofocus Signal Calculation Unit 88 Offset Calculation Unit 100 Inspection Device 101 Inspected Substrate 102 XYθ worktable 103 light source 104 Magnification Optical System 105 camera sensor 106 sensor circuit 107 position circuit 108 comparator circuit 109 disk devices 110 control computer 111 memory 112. Create a circuit based on the image. 113 Automatic Loader Control Circuit 114 Workbench Control Circuit 115 magnetic tape device 116 FD 117 CR 118 Pattern Monitor 119 printer 120 bus 122 Laser Length Measurement System 123-strip pattern memory 130 Automatic Loader 131 Automatic Focusing Mechanism 132 Z-drive mechanism 134 position sensor 140 Autofocus Control Circuit 150 Optical Image Acquisition Mechanism 160 control system circuit 170 Transmission Illumination Optical System 171 Reflective Illumination Optical System 174 beam splitter 175. Inspect the optical system. 176 collimating lens 177 beam splitter 178 Imaging Optical System 180° autofocus optical system 181 Imaging Optical System 182 beam splitter 184, 186 slotted plates 185, 187 light sensors

Claims

1. A pattern inspection device, characterized in that, have: Worktable, on which the substrate is placed; A drive mechanism that moves the height of the worktable. The relevant data generation circuit uses an autofocus signal for autofocus control parameters and a focus evaluation value for evaluating the focus position, obtained while the height position of the pattern forming surface of the evaluation substrate is variable, when an evaluation substrate with an evaluation pattern is placed on the worktable, to generate relevant data between the autofocus signal and the focus evaluation value. Storage device for storing the relevant data; An inspection autofocus signal calculation circuit uses the autofocus signal at each height position, the focus evaluation value, and the relevant data of the evaluation substrate, obtained while the substrate to be inspected with a patterned surface is placed on the worktable, to calculate an inspection autofocus signal that yields a focus evaluation value of at least a threshold value in the substrate to be inspected. An autofocus mechanism adjusts the height position of the pattern forming surface of the substrate under inspection to a height position of the pattern forming surface corresponding to the value of the autofocus signal for inspection. The sensor receives light transmitted or reflected from the substrate under inspection by the inspection light when the height position of the pattern forming surface of the substrate under inspection is adjusted to the height position of the pattern forming surface corresponding to the value of the inspection autofocus signal, thereby capturing an optical image of the substrate under inspection. as well as The comparison circuit compares the captured optical pixels with the reference image.

2. The pattern inspection device according to claim 1, characterized in that, The relevant data is obtained by approximating the autofocus signal and the focus evaluation value at each height position using a function.

3. The pattern inspection device according to claim 1, characterized in that, As the relevant data, the numerical columns of the autofocus signal and the focus evaluation value at each height position are used.

4. The pattern inspection device according to claim 1, characterized in that, The autofocus signal and focus evaluation value of the substrate under inspection are obtained at more than 3 different height positions at each height position.

5. The pattern inspection device according to claim 1, characterized in that, The relevant data generation circuit has the following features: The plotting processing circuit plots the autofocus signal at each acquired height position and the focus evaluation value of each autofocus signal; and The fitting processing circuit uses a convex polynomial function to approximate the focus evaluation value of each plotted autofocus signal value.

6. The pattern inspection device according to claim 1, characterized in that, The inspection autofocus signal calculation circuit plots multiple combinations of the autofocus signal and the focus evaluation value obtained on the inspected substrate to create a curve, and applies the template representing the relevant data to the plotted multiple combinations.

7. The pattern inspection device according to claim 6, characterized in that, The inspection autofocus signal calculation circuit calculates the inspection autofocus signal with a focus evaluation value above the threshold in the curve graph of the template.

8. The pattern inspection device according to claim 7, characterized in that, The inspection autofocus signal calculation circuit calculates the inspection autofocus signal corresponding to the maximum value of the applied template.

9. A method for adjusting the focus position, characterized in that, Using an evaluation substrate with an evaluation pattern formed on it, placed on a worktable, and while allowing the height position of the pattern forming surface of the evaluation substrate to be variable, autofocus signals for parameters used for autofocus control at each height position and focus evaluation values ​​for evaluating the focus position are obtained, and correlation data between the autofocus signals and the focus evaluation values ​​is generated. The relevant data is stored in a storage device. Using an inspected substrate with a patterned surface placed on the worktable, and while the height of the patterned surface of the inspected substrate is variable, the autofocus signal and focus evaluation value at each height position, along with the relevant data of the evaluation substrate, are used to calculate an inspection autofocus signal that yields a focus evaluation value above a threshold on the inspected substrate. The system receives light transmitted or reflected from the substrate under inspection by the inspection light, thereby adjusting the height position of the pattern forming surface of the substrate under inspection to the height position of the pattern forming surface corresponding to the value of the inspection autofocus signal when an optical image of the substrate under inspection is captured by a sensor.

10. A pattern inspection method, characterized in that, Using an evaluation substrate with an evaluation pattern formed on it, placed on a worktable, and while allowing the height position of the pattern forming surface of the evaluation substrate to be variable, autofocus signals for parameters used for autofocus control at each height position and focus evaluation values ​​for evaluating the focus position are obtained, and correlation data between the autofocus signals and the focus evaluation values ​​is generated. The relevant data is stored in a storage device. Using an inspected substrate with a patterned surface placed on the worktable, and while the height of the patterned surface of the inspected substrate is variable, the autofocus signal and focus evaluation value at each height position, along with the relevant data of the evaluation substrate, are used to calculate an inspection autofocus signal that yields a focus evaluation value above a threshold on the inspected substrate. While adjusting the height of the pattern-forming surface of the substrate under inspection to correspond to the value of the inspection autofocus signal, the system receives light transmitted or reflected from the substrate under inspection by the inspection light, thereby capturing an optical image of the substrate under inspection using a sensor. The captured optical pixels are compared with the reference image, and the results are output.

Images