Pattern inspection device, focal point position adjustment method, and pattern inspection method

Abstract

To provide an inspection device that can acquire parameters required during an autofocus operation of the substrate to be inspected in a shorter time than before.SOLUTION: A pattern inspection device comprises: a correlation data creation part that creates correlation data between an autofocus signal and a focus evaluation value for each height position acquired while varying a height position of a pattern forming surface of an evaluation substrate; a storage device for storing the correlation data; an inspection autofocus signal calculation part that calculates an inspection autofocus signal with which a focus evaluation value equal to or greater than a threshold can be obtained for the substrate to be inspected by using the autofocus signal and the focus evaluation value for each height position acquired while varying the height position of the pattern forming surface of the substrate to be inspected in a state in which the substrate to be inspected having a graphic pattern formed thereon is placed on the stage; and an autofocus mechanism that adjusts 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 a value of the inspection autofocus signal.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a pattern inspection apparatus, a focal position adjustment method, and a pattern inspection method, for example, to an apparatus for inspecting pattern defects of an exposure mask used in semiconductor manufacturing, and a focal position adjustment method for the apparatus. [Background technology]

[0002] In recent years, with the increasing integration and capacity of large scale integrated circuits (LSI), the circuit line width required for semiconductor elements has become increasingly narrow. These semiconductor elements are manufactured by forming circuits by exposing and transferring a pattern onto a wafer using a reduced projection exposure device called a stepper, using an original pattern (also called a mask or reticle, hereafter collectively referred to as a mask) on which a circuit pattern is formed.

[0003] Improving yield is essential for the manufacture of LSIs, which are very costly to manufacture. One of the major factors that reduce yield is pattern defects in the masks used when exposing and transferring ultra-fine patterns onto semiconductor wafers using photolithography technology. In recent years, as the dimensions of LSI patterns formed on semiconductor wafers become finer, the dimensions that must be detected as pattern defects have become extremely small. This has created a need for high-precision pattern inspection equipment that inspects for defects in transfer masks used in LSI manufacturing.

[0004] Inspection techniques include, for example, "die-to-die inspection," which compares optical image data captured of the same pattern at different locations on the same mask, and "die-to-database inspection," which inputs drawing data (design data) converted from CAD data used to design the pattern into an equipment input format for input by a drawing device when drawing the pattern on a mask into an inspection device, generates a reference image based on this, and compares this with an optical image that serves as measurement data captured of the pattern.

[0005] In such an inspection device, it is necessary to obtain a clear image of the pattern on the mask, which is the object to be inspected. However, since the optical system of the inspection device has a finite focal depth, it is necessary to keep the inspection surface of the object to be inspected within the focal depth of the optical system during inspection. In other words, it is required to keep the contrast of the captured image within an allowable range. In the inspection device, it is necessary to scan the mask while moving the stage and capture images continuously, and it is not realistic to calculate the image contrast and adjust the focus of the optical system sequentially during inspection because of insufficient processing time.

[0006] Therefore, in the inspection device, in addition to the inspection optical system for capturing an image, an autofocus mechanism is adopted that detects the displacement of the object to be inspected in the height direction relative to the inspection optical system and adjusts the height position.

[0007] With the recent trend toward finer patterns, the wavelength of inspection light is becoming shorter. Accordingly, the focal depth of the inspection optical system has become shallower. Therefore, while the accuracy of the measurement system of an independent autofocus mechanism installed near the inspection optical system was previously sufficient, it has become impossible to detect various fluctuation factors (dependence on temperature / mechanical deformation) of the inspection optical system without performing in-situ measurements using the inspection optical system itself, and it has become impossible to perform high-precision focus adjustment. For this reason, a form that partially uses the inspection optical system as an autofocus mechanism has been adopted (for example, see Patent Document 1).

[0008] In the optical system of such an autofocus mechanism, the amount of light passing through slits arranged before and after the focal position of the image from the mask is measured, and the difference between the two measured amounts of light is calculated to measure the change in the height position of the mask. Here, an error occurs between the height position at which the difference between the measured amount of light is zero and the height position at which the image contrast is maximized. For this reason, it is necessary to obtain parameters required for the autofocus operation at which the image contrast is increased for each mask to be inspected. On the other hand, in order to obtain parameters required for the autofocus operation at which the image contrast is increased, relationship data between the two is required, and it takes time to carry out the process to obtain this relationship data. In order to reduce the inspection time and thereby improve the throughput, it is necessary to reduce the time required for the process to obtain parameters required for the autofocus operation at which the image contrast is increased. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2020-125941 A Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, one aspect of the present invention provides an inspection device and method that can acquire parameters required for autofocus operation of a substrate to be inspected in a shorter time than conventionally possible. [Means for solving the problem]

[0011] A pattern inspection apparatus according to one aspect of the present invention comprises: A stage on which a substrate is placed; A drive mechanism for moving the height position of the stage; a correlation data creation unit that creates correlation data between an autofocus signal and a focus evaluation value, using an autofocus signal used as a parameter for autofocus control and a focus evaluation value for evaluating a focus position, the autofocus signal and the focus evaluation value being acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate, with the evaluation substrate having an evaluation pattern formed thereon, in a state where the evaluation substrate is placed on a stage; A storage device for storing correlation data; an inspection autofocus signal calculation unit that calculates an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using autofocus signals and focus evaluation values ​​acquired for each height position while varying the height position of the pattern formation surface of the substrate to be inspected in a state where the substrate to be inspected, on which a geometric pattern is formed, is placed on a stage, and correlation data on the evaluation substrate; an autofocus mechanism that adjusts the height position of the pattern-formed surface of the substrate to a height position of the pattern-formed surface corresponding to the value of the inspection autofocus signal; a sensor that captures an optical image of the substrate to be inspected by receiving light that is irradiated with inspection light and transmitted through or reflected from the substrate to be inspected, while the height position of the pattern-formed surface of the substrate to be inspected is adjusted to a height position of the pattern-formed surface that corresponds to the value of the inspection autofocus signal; a comparison unit that uses a reference image to compare the captured optical pixels with the reference image; The present invention is characterized by comprising:

[0012] In addition, it is preferable to use, as the correlation data, a function obtained by approximating the autofocus signal and the focus evaluation value for each height position.

[0013] Alternatively, it is preferable to use a numerical sequence of the autofocus signal and the focus evaluation value for each height position as the correlation data.

[0014] Also, it is preferable that the autofocus signal and the focus evaluation value for each height position on the inspected substrate are obtained at three or more different height positions.

[0015] A focus position adjustment method according to one aspect of the present invention includes: creating correlation data between the autofocus signal and the focus evaluation value, using the autofocus signal used as a parameter for autofocus control and the focus evaluation value for evaluating the focus position, acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate with the evaluation pattern formed thereon in a state where the evaluation substrate is placed on a stage; storing the correlation data in a storage device; a step of calculating an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using autofocus signals and focus evaluation values ​​acquired for each height position while varying the height position of the pattern-formed surface of the substrate to be inspected in a state in which the substrate to be inspected, on which a geometric pattern is formed, is placed on a stage, and correlation data on the evaluation substrate; a step of adjusting a height position of the pattern-formed surface of the substrate to a height position corresponding to a value of an inspection autofocus signal when an optical image of the substrate is captured by a sensor by receiving light that is transmitted through or reflected by the substrate irradiated with the inspection light; The present invention is characterized by comprising:

[0016] A pattern inspection method according to one aspect of the present invention includes: creating correlation data between the autofocus signal and the focus evaluation value, using the autofocus signal used as a parameter for autofocus control and the focus evaluation value for evaluating the focus position, acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate with the evaluation pattern formed thereon in a state where the evaluation substrate is placed on a stage; storing the correlation data in a storage device; a step of calculating an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using autofocus signals and focus evaluation values ​​acquired for each height position while varying the height position of the pattern-formed surface of the substrate to be inspected in a state in which the substrate to be inspected has a graphic pattern formed thereon and correlation data on the evaluation substrate; a step of capturing an optical image of the substrate to be inspected by a sensor by receiving light that is irradiated with inspection light and transmitted through or reflected from the substrate to be inspected while adjusting the height position of the pattern-formed surface of the substrate to be inspected to a height position of the pattern-formed surface that corresponds to the value of the inspection autofocus signal; using a reference image to compare the captured optical pixels with the reference image and output the result; The present invention is characterized by comprising: Effect of the Invention

[0017] According to one aspect of the present invention, parameters required for autofocus operation of a substrate to be inspected can be obtained in a shorter time than in the past. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a configuration diagram showing a configuration of a pattern inspection device according to a first embodiment. [Diagram 2] FIG. 2 is a conceptual diagram for explaining an inspection region in the first embodiment. [Diagram 3] FIG. 13 is a diagram showing an example of a measurement result of the amount of light for autofocus control in a comparative example of the first embodiment. [Figure 4] FIG. 13 is a diagram showing an example of an autofocus signal in a comparative example to the first embodiment. [Diagram 5] FIG. 4 is a flow chart showing an example of some of the main steps of the inspection method according to the first embodiment. [Figure 6] 13 is a flowchart showing the remaining steps of the example of the main steps of the inspection method according to the first embodiment. FIG. [Figure 7] 2 is a block diagram showing an example of the internal configuration of an autofocus control circuit in the first embodiment. FIG. [Figure 8] FIG. 4 is a diagram for explaining an example of a method for calculating contrast in the first embodiment. [Figure 9] FIG. 11 is a diagram for explaining another example of the method for calculating contrast in the first embodiment. [Figure 10]FIG. 4 is a diagram for explaining an example of a technique for calculating brightness in the first embodiment. [Figure 11] 6 is a diagram showing plots of focus evaluation values ​​of autofocus signal values ​​of the evaluation board in the first embodiment. FIG. [Figure 12] 5 is a diagram showing plots of focus evaluation values ​​of autofocus signal values ​​of an inspected substrate in the first embodiment. FIG. [Figure 13] FIG. 4 is a diagram for explaining a filter process in the first embodiment. [Figure 14] 4 is a diagram showing an example of an internal configuration of a comparison circuit according to the first embodiment; FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Embodiment 1 Fig. 1 is a configuration diagram showing the configuration of a pattern inspection apparatus in embodiment 1. In Fig. 1, an inspection apparatus 100 for inspecting a substrate to be inspected, for example, a pattern formed on a mask, includes an optical image acquisition mechanism 150 and a control circuit 160.

[0020] The optical image acquisition mechanism 150 includes a light source 103, a reflection illumination optical system 171, a movably arranged XYθ table 102, a magnification optical system 104, a beam splitter 174, a beam splitter 177, a collimator lens 176, an imaging optical system 178, an autofocus mechanism 131, an image sensor 105, a sensor circuit 106, a stripe pattern memory 123, a laser measurement system 122, and an autoloader 130. When a transmission inspection using transmitted light is performed, a transmission illumination optical system 170 is further arranged. When only a reflection inspection using reflected light is performed without performing a transmission inspection, the transmission illumination optical system 170 may be omitted. When both a transmission inspection and a reflection inspection are performed simultaneously, an image sensor (not shown) may be further added, and the image sensor 105 captures an image for the reflection inspection, and the added image sensor captures an image for the transmission inspection.

[0021] The autofocus mechanism 131 has an autofocus optical system 180, a light amount sensor 185 (first light amount sensor), a light amount sensor 187 (second light amount sensor), a Z drive mechanism 132, and a position sensor .

[0022] The autofocus optical system 180 includes an imaging optical system 181, a beam splitter 182, a slit plate 184, and a slit plate 186. The autofocus optical system 180 guides light transmitted through or reflected from the substrate to a light amount sensor 185 and a light amount sensor 187. The beam splitter 182 is disposed in front of the focal position. The slit plate 184 is disposed at a front focal position (front focus position) and receives light transmitted through the beam splitter 182. The light amount sensor 185 measures the amount of light that has passed through the slit plate 184 disposed at the front focal position (front focus position). The slit plate 186 is disposed at a back focal position (back focus position) and receives light branched by the beam splitter 182. The light amount sensor 187 measures the amount of light that has passed through the slit plate 186 disposed at a back focal position (back focus position).

[0023] The inspected substrate 101, which has been transferred from the autoloader 130, is placed on the XYθ table 102. The inspected substrate 101 includes, for example, a photomask for exposure that transfers a pattern onto a semiconductor substrate such as a wafer. In addition, a graphic pattern to be inspected is formed on this photomask. The substrate 101 is placed on the XYθ table 102 with, for example, the pattern-formed surface facing downward. This is an example of a stage of the XYθ table 102.

[0024] A line sensor or a two-dimensional sensor is used as the imaging sensor 105. For example, a TDI (time delay integration) sensor is preferably used. The TDI sensor has a plurality of photosensor elements arranged two-dimensionally. A predetermined image accumulation time is set for each photosensor element when capturing an image. In the TDI sensor, the output of a plurality of photosensor elements arranged in the scanning direction is integrated and output. The plurality of photosensor elements arranged in the scanning direction capture the same pixel while shifting the time according to the movement of the XYθ table 102. When a line sensor is used, the plurality of photosensor elements are arranged so as to be lined up in a direction perpendicular to the scanning direction.

[0025] In the control system circuit 160, a control computer 110 that controls the entire inspection apparatus 100 is connected to a position circuit 107, a comparison circuit 108, a reference image creation circuit 112, an autoloader control circuit 113, a table control circuit 114, an autofocus control circuit 140, a magnetic disk device 109, a memory 111, a magnetic tape device 115, a flexible disk device (FD) 116, a CRT 117, a pattern monitor 118, and a printer 119 via a bus 120. In addition, the imaging sensor 105 is connected to a stripe pattern memory 123, which is connected to the comparison circuit 108. In addition, the reference image creation circuit 112 is connected to the comparison circuit 108.

[0026] The output of the position sensor 134 is connected to the autofocus control circuit 140. In addition, the outputs of the light amount sensors 185 and 187 are connected to the autofocus control circuit 140.

[0027] In addition, a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the autofocus control circuit 140 have a processing circuit. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Each circuit may be configured using the same processing circuit (one processing circuit), or different processing circuits (separate processing circuits). For example, a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the autofocus control circuit 140 may be configured and executed by the control computer 110. Input data or calculated results required for the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the autofocus control circuit 140 are stored in a memory (not shown) in each circuit or in the memory 111 each time. Input data required for the control computer 110 or the results of calculations are stored in a memory (not shown) in the control computer 110 or in the memory 111 each time. The programs for executing the processor and the like may be recorded on a recording medium such as the magnetic disk device 109, the magnetic tape device 115, the FD 116, or a ROM (read only memory).

[0028] The inspection device 100 is equipped with a reflection inspection optical system and / or a transmission inspection optical system as the inspection optical system 175. A high-magnification reflection inspection optical system is configured by the light source 103, the reflection illumination optical system 171, the beam splitter 174, the magnification optical system 104, the XYθ table 102, the collimator lens 176, and the imaging optical system 178. Alternatively, a high-magnification transmission inspection optical system is configured by the light source 103, the transmission illumination optical system 170, the XYθ table 102, the magnification optical system 104, the collimator lens 176, and the imaging optical system 178.

[0029] The XYθ table 102 is driven by a table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (XY-θ) motor that drives in the X, Y, and θ directions. These X, Y, and θ motors can be, for example, step motors. The XYθ table 102 can be moved in the horizontal and rotational directions by motors of the XYθ axes. The XYθ table 102 is an example of a stage. The movement position of the substrate 101 placed on the XYθ table 102 is measured by a laser length measurement system 122 and supplied to a position circuit 107. The transport of the substrate 101 from the autoloader 130 to the XYθ table 102 and the transport process of the substrate 101 from the XYθ table 102 to the autoloader 130 are controlled by an autoloader control circuit 113.

[0030] Furthermore, the XYθ table 102 is driven in the z direction by a Z driving mechanism 132 controlled by an autofocus control circuit 140. For example, a piezoelectric element or a step motor is preferably used as the Z driving mechanism 132. Furthermore, the height position of the XYθ table 102 is measured by a position sensor 134, and the measurement result is output to the autofocus control circuit 140.

[0031] Drawing data (design data) that is the basis for forming a pattern on the inspected substrate 101 is input from outside the inspection device 100 and stored in the magnetic disk device 109. In the drawing data, a plurality of graphic patterns are defined, and each graphic pattern is usually composed of a combination of a plurality of element graphics. Note that a graphic pattern composed of a single graphic may also exist. On the inspected substrate 101, a corresponding pattern is formed based on each of the graphic patterns defined in the drawing data.

[0032] 1 illustrates components necessary for explaining the embodiment 1. It goes without saying that the inspection device 100 may include other components that are normally required.

[0033] 2 is a conceptual diagram for explaining the inspection area in the first embodiment. As shown in FIG. 2, the inspection area 10 (whole inspection area) of the substrate 101 is virtually divided into a plurality of rectangular inspection stripes 20 having a scan width W of the image sensor 105, for example, in the Y direction. The inspection device 100 then acquires an image (stripe area image) for each inspection stripe 20. For each inspection stripe 20, an image of a figure pattern arranged within the inspection stripe 20 is captured in the longitudinal direction (X direction) of the stripe area using a laser beam (inspection beam). In order to prevent missing an image, it is preferable that the inspection stripes 20 are set so that adjacent inspection stripes 20 overlap with each other by a predetermined margin width.

[0034] The movement of the XYθ table 102 causes the image sensor 105 to move continuously in the X direction relative to the object, thereby acquiring optical images. The image sensor 105 continuously captures optical images of a scan width W as shown in FIG. 2. In the first embodiment, after capturing an optical image of one inspection stripe 20, the image sensor 105 moves in the Y direction to the position of the next inspection stripe 20, and then moves in the reverse direction to similarly capture optical images of the scan width W continuously. That is, imaging is repeated in the forward (FWD)-backward (BWD) directions, which are opposite directions, on the outward and return paths.

[0035] Furthermore, for actual inspection, the stripe region image of each inspection stripe 20 is divided into a plurality of rectangular frame region 30 images (frame images 31) as shown in Fig. 2. Then, inspection is performed for each frame image 31 of the frame region 30. For example, it is divided into a size of 512 x 512 pixels. Therefore, a reference image to be compared with the frame images 31 of the frame region 30 is also created for each frame region 30.

[0036] Here, the imaging direction is not limited to the repetition of forward (FWD)-backward (BWD). Imaging may be performed from one direction. For example, FWD-FWD may be repeated. Or, BWD-BWD may be repeated.

[0037] As described above, the inspection device 100 is equipped with, in addition to the inspection optical system 175 (the reflection inspection optical system and / or the transmission inspection optical system), an autofocus mechanism 131 that detects the vertical displacement of the substrate 101, which is the object to be inspected, relative to the inspection optical system 175.

[0038] Here, as patterns become finer, the wavelength of the inspection light is becoming shorter, and as a result, the focal depth of the inspection optical system 175 becomes shallower. Therefore, while the accuracy of an independent measurement system installed near the inspection optical system was previously sufficient, it has become impossible to detect various fluctuation factors (temperature / mechanical deformation dependence) of the inspection optical system without performing (in-situ) measurements using the inspection optical system itself, making it impossible to perform high-precision focus adjustment.

[0039] That is, the autofocus mechanism is required to have the function of detecting (monitoring) changes in the state of the inspection optical system, in addition to the signal output change (sensor output) associated with changes in mask height. In order for the autofocus optical system to utilize the inspection optical system, there was a transition from a method of using an objective lens (with dual-wavelength aberration correction) adapted to the original measurement light source (red laser) to a method of providing an optical system using DUV light, which is the inspection light, due to the demand for even higher accuracy in the objective lens.

[0040] FIG. 3 is a diagram showing an example of a measurement result of the light amount for autofocus control in a comparative example of the first embodiment. The comparative example of FIG. 3 shows signal changes of the light amount signal AF-F at the front focal position and the light amount signal AF-R at the back focal position with respect to the height position of the pattern formation surface of the mask measured by the confocal optical system. The light amount signal AF-F and the light amount signal AF-F ideally show symmetrical changes with respect to the maximum value. Furthermore, the light amount signal AF-F and the light amount signal AF-F ideally show the same distribution. Therefore, the light amount signal AF-F and the light amount signal AF-F ideally change symmetrically with respect to the focal position. In such a case, the value (autofocus signal: AF signal) obtained by dividing the difference between the light amount signal AF-F and the light amount signal AF-R by the sum changes linearly with respect to the change in the height position of the pattern formation surface of the mask.

[0041] Therefore, the height position of the mask pattern formation surface is changed, and the autofocus signal and the contrast of the resulting image are obtained for each height position. Then, a correlation graph between the autofocus signal and the image contrast is created, and the autofocus signal that maximizes the contrast is calculated as the autofocus signal for the focal position. In the autofocus mechanism, the autofocus signal is fed back as a stage displacement signal, and the stage height is adjusted so that the autofocus signal becomes the autofocus signal for the focal position.

[0042] However, the light reaching the slit plates 184 and 186 changes its distribution differently when the height of the pattern-forming surface of the mask is changed due to astigmatism caused by the performance variation of the optical elements, deviation in optical adjustment, etc., and as a result, the light intensity signals that pass through the slit plates 184 and 186 and are measured by the light intensity sensors 185 and 187 may not change symmetrically around the maximum value with respect to the change in the height position of the mask. The comparative example of Figure 3 shows a case where a deviation occurs when the light intensity signal AF-R at the back focal position is inverted and superimposed on the light intensity signal AF-F at the front focal position. In this way, the light intensity signal AF-R and the light intensity signal AF-F do not change symmetrically with respect to the focal position.

[0043] FIG. 4 is a diagram showing an example of an autofocus signal in a comparative example of the first embodiment. The autofocus signal can be defined as a value obtained 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 signal AF-F and the light intensity signal AF-R have the same distribution, changing symmetrically on the left and right sides of a maximum value, the autofocus signal is proportional to the change in the height position of the mask's pattern forming surface. However, as shown in the comparative example of FIG. 4, the autofocus signal does not change linearly or is not proportional to the change in the height position of the mask's pattern forming surface. Therefore, the autofocus signal generates a nonlinear error with respect to the change in the height position of the mask's pattern forming surface.

[0044] Therefore, the correlation graph between the autofocus signal and the image contrast is an asymmetric graph. For each substrate to be inspected, such a correlation graph is obtained, and the autofocus signal with the maximum contrast of the correlation graph becomes the inspection autofocus signal for that substrate to be inspected. However, since the graph is complicated and asymmetric, the approximation error increases when the number of measurement points is small. Therefore, when the number of measurement points is small, a highly accurate inspection autofocus signal cannot be obtained. On the other hand, if many measurement points are measured for each substrate to be inspected, the process to obtain the inspection autofocus signal takes time. In order to shorten the inspection time and thus improve the throughput, it is required to shorten the time required for the process to obtain the inspection autofocus signal with a larger image contrast.

[0045] Therefore, in the first embodiment, instead of obtaining such a highly accurate correlation graph using a test board, the correlation graph is obtained in advance, for example, when manufacturing and assembling the inspection device 100, using an evaluation board. Then, during actual inspection, the correlation graph obtained using the evaluation board is applied to the results obtained using a small number of measurement points on the test board to calculate an inspection autofocus signal for the test board. This will be explained in detail below.

[0046] FIG. 5 is a flow chart showing an example of some of the main steps of the inspection method according to the first embodiment. FIG. 6 is a flow chart showing the remaining steps of the example of the main steps of the inspection method according to the first embodiment. 5 and 6, the inspection method in the first embodiment performs a series of steps including an evaluation substrate loading step (S102), an evaluation substrate height position setting and measurement step (S104), a light intensity measurement step (S106), an autofocus signal calculation step (S108), an optical image acquisition step (S110), a focus evaluation value calculation step (S112), a correlation data creation step (S120), an inspection substrate loading step (S202), an inspection substrate height position setting and measurement step (S204), a light intensity measurement step (S206), an autofocus signal calculation step (S208), an optical image acquisition step (S210), a focus evaluation value calculation step (S212), a measurement value plotting step (S220), an inspection autofocus signal calculation step (S222), an image acquisition (autofocus control) step (S250), and a comparison step (S252). The correlation data creation step (S120) includes, as internal steps, a measurement value plotting step (S122) and a function approximation step (S124).

[0047] In the evaluation substrate loading step (S102), the evaluation substrate transferred from the autoloader 130 is placed on the XYθ table 102.

[0048] Fig. 7 is a block diagram showing an example of the internal configuration of the autofocus control circuit in embodiment 1. In Fig. 7, autofocus control circuit 140 includes storage devices 51, 57, and 61 such as magnetic disk devices, an autofocus signal calculation unit 50, an evaluation value calculation unit 52, a correlation data creation unit 53, a stage 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 plot processing unit 84, an inspection autofocus signal calculation unit 86, and an offset calculation unit 88. In the correlation data creation unit 53, a plot processing unit 54 and a fitting processing unit 56 are disposed. A series of "~ units" such as the autofocus signal calculation unit 50, the evaluation value calculation unit 52, the correlation data creation unit 53 (plot processing unit 54 and fitting processing unit 56), the stage height control unit 62, the autofocus signal calculation unit 64, the autofocus processing unit 66, the autofocus signal calculation unit 80, the evaluation value calculation unit 82, the plot processing unit 84, the inspection autofocus signal calculation unit 86, and the offset calculation unit 88 have processing circuits. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, semiconductor devices, and the like. In addition, each of the "~ units" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. The input data or calculated results required for the autofocus signal calculation unit 50, the evaluation value calculation unit 52, the correlation data creation unit 53 (plot processing unit 54 and fitting processing unit 56), the stage height control unit 62, the autofocus signal calculation unit 64, the autofocus processing unit 66, the autofocus signal calculation unit 80, the evaluation value calculation unit 82, the plot processing unit 84, the inspection autofocus signal calculation unit 86, and the offset calculation unit 88 are stored each time in a memory (not shown) in the autofocus control circuit 140 or in memory 111.

[0049] In the evaluation substrate height position setting and measurement step (S104), the evaluation substrate height position (pattern formation surface height position) is variably set by driving the height position of the XYθ table 102 by the Z drive mechanism 132 under the control of the stage height control unit 62. In addition, 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.

[0050] An evaluation pattern is formed on the evaluation substrate. As the evaluation pattern, for example, a line and space pattern can be used. For example, a 1:1 line and space pattern is used. Alternatively, a hole pattern with a predetermined pattern density (e.g., 50%) can be used. The line width size d of these evaluation patterns can be defined by the following formula (1) using the light source wavelength λ of the inspection apparatus 100 and the numerical aperture NA of the optical system. It is preferable to set k to a value greater than 1. For example, it is preferable to set it to a value in the range of 1 < k < 10. (1) λ / (2NA) ≦ d ≦ k(λ / (2NA))

[0051] As the light intensity measurement step (S106), with the evaluation substrate height position controlled to the height position hi, the light quantity at the front focal position of the light transmitted or reflected from the evaluation substrate irradiated with the inspection light is measured by the light quantity sensor 185. Similarly, the light quantity at the rear focal position is measured by the light quantity sensor 187. Specifically, it operates as follows. i indicates an index.

[0052] Laser light (e.g., DUV light) having a wavelength in the ultraviolet region or below, which becomes inspection light, is irradiated from an appropriate light source 103 to a beam splitter 174 by a reflection illumination optical system 171. The irradiated laser light is reflected by the beam splitter 174 and irradiated onto the evaluation substrate by an enlargement optical system 104. The light reflected from the evaluation substrate passes through the enlargement optical system 104 and the beam splitter 174 and irradiates the beam splitter 177. The light branched by the beam splitter 177 enters an autofocus optical system 180.

[0053] Light incident on the autofocus optical system 180 is refracted in the light-collecting direction by the imaging optical system 181, and irradiates the beam splitter 182. The light transmitted through the beam splitter 182 is partially restricted by a slit plate 184 at the front focal position (front focus position), and the amount of light passing through the slit plate 184 is measured by a light amount sensor 185. The light branched from the beam splitter 182 is partially restricted by a slit plate 186 at the back focal position (back focus position), and the amount of light passing through the slit plate 186 is measured by a light amount sensor 187. This makes it possible to measure the amount of light at the front focus position and the back focus position at the height position hi. The measured light amount data (light intensity data) of the light amount at the front focus position and the light amount at the back focus position at the height position hi is stored in the storage device 51.

[0054] In the autofocus signal calculation step (S108), the autofocus signal calculation unit 50 calculates an autofocus signal εi used as a parameter for autofocus control when the evaluation substrate height position is height position hi. The autofocus signal εi is defined by the following equation (2) using the amount of light Ai at the front focal position and the amount of light Bi at the back focal position, where i represents an index. (2) εi=(Ai-Bi) / (Ai+Bi)

[0055] The value of the autofocus signal ε i is stored, for example in a storage device 51, in association with the height position hi.

[0056] In the optical image acquiring step (S110), the optical image acquiring mechanism 150, with the evaluation board placed on the XYθ table 102, captures an optical image of the evaluation board at a set height position hi by receiving light irradiated with inspection light and transmitted through or reflected from the evaluation board at the imaging sensor 105 via the inspection optical system 175. Specifically, the operation is as follows.

[0057] The optical image acquisition mechanism 150 scans the inspection stripe 20 including the preset frame region 30 of the evaluation substrate with a laser beam (inspection beam) and captures an image of the stripe region with the imaging sensor 105. Specifically, it operates as follows. The XYθ table 102 is moved to a position where the inspection stripe 20 of the evaluation substrate to be imaged can be captured. In the transmission inspection, the pattern formed on the evaluation substrate is irradiated with a laser beam (e.g., DUV beam) having a wavelength of ultraviolet or less, which serves as inspection beam, from an appropriate light source 103 via the transmission illumination optical system 170. In other words, the transmission illumination optical system 170 illuminates the evaluation substrate on which the pattern is formed. The light transmitted through the evaluation substrate is passed through the magnifying optical system 104 and the collimator lens 176, and is focused as an optical image by the imaging optical system 178 on the imaging sensor 105 (an example of a sensor), and is incident thereon.

[0058] Alternatively, in a reflection inspection, a laser light having a wavelength of ultraviolet or less (e.g., DUV light) serving as inspection light is emitted from an appropriate light source 103 to a beam splitter 174 via a reflection illumination optical system 171. The irradiated laser light is reflected by the beam splitter 174 and is irradiated onto the evaluation substrate by the magnifying optical system 104. The light reflected from the evaluation substrate passes through the magnifying optical system 104, the beam splitter 174, and a collimator lens 176, and is focused as an optical image by the imaging optical system 178 on the imaging sensor 105, where it is incident.

[0059] The imaging sensor 105 captures an optical image of the evaluation substrate.

[0060] The pattern image formed on the image sensor 105 is photoelectrically converted by each photosensor element of the image sensor 105, and further A / D (analog-to-digital) converted by the sensor circuit 106. Then, pixel value data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (amount of light) of each pixel. Then, of the inspection stripe image, a frame image 31 (measurement image) of a preset frame area 30 is output to the autofocus control circuit 140 and stored in the storage device 61.

[0061] In the focus evaluation value calculation step (S112), the evaluation value calculation unit 52 calculates a focus evaluation value from the obtained image. As the focus evaluation value, for example, one of the contrast and brightness obtained from the optical image is used.

[0062] Fig. 8 is a diagram for explaining an example of a method for calculating contrast in the first embodiment. The example of Fig. 8 shows a case where a line-and-space pattern, which is an example of an evaluation pattern, is captured in the measurement image. In this case, the contrast of the gradation data of each of a plurality of lines in a direction (x direction) perpendicular to the direction (y direction) in which the line pattern (or space pattern) extends is calculated. The contrast C can be defined by the following formula (3) using the maximum and minimum values ​​of the gradation data. (3) C = (maximum value - minimum value) / (maximum value + minimum value)

[0063] Then, for example, the average value of the contrast of all the lines is calculated as the contrast of the image. Note that, in order to reduce measurement variations, it is desirable to use the average value of the contrast of as many lines as possible, but this is not limited to all the lines.

[0064] 9 is a diagram for explaining another example of a method for calculating contrast in the first embodiment. The example in FIG. 9 shows a case where a hole pattern, which is another example of an evaluation pattern, is captured in the measurement image. In this case, the contrast of the gradation data of each line of a plurality of lines, for example, in the x direction, perpendicular to the y direction, is calculated at a plurality of positions, for example, in the y direction, that overlap with the hole pattern. The contrast C can be defined by the above-mentioned formula (3) using the maximum and minimum values ​​of the gradation data.

[0065] Then, for example, the average value of the contrast of all the lines is calculated as the contrast of the image of the evaluation board.

[0066] Fig. 10 is a diagram for explaining an example of a method for calculating brightness in the first embodiment. In the example of Fig. 10, an example of a histogram is shown in which the vertical axis indicates the number of pixels (frequency) and the horizontal axis indicates the gradation value. Such a histogram is created using all pixels in the measured image. Then, the total number of pixels showing a gradation value equal to or greater than a threshold value Th is defined as the brightness of the image.

[0067] Then, returning to the evaluation substrate height position setting and measurement step (S104), each step 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. In this way, an optical image of the evaluation substrate is acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate. Also, an AF signal is acquired for each height position. Then, the evaluation value calculation unit 52 calculates a focus evaluation value for evaluating the focus position for each height position while varying the height position of the pattern formation surface of the evaluation substrate on which the figure pattern is formed. AF signals and focus evaluation values ​​are acquired at four or more height positions. More preferably, AF signals and focus evaluation values ​​are acquired at ten or more height positions. This is preferable.

[0068] In the correlation data creating step (S120), the correlation data creating unit 53 creates correlation data between the AF signal and the focus evaluation value, using an autofocus signal (AF signal) used as a parameter for autofocus control and a focus evaluation value for evaluating the focus position, which are acquired while varying the height position of the pattern forming surface of the evaluation substrate, on which an evaluation pattern is formed, with the evaluation substrate placed on the XYθ table 102 (stage). A specific description will be given below.

[0069] As a measurement value plotting step (S122), the plot processing unit 54 plots the focus evaluation value of each acquired AF signal value in a coordinate system in which the vertical axis indicates the focus evaluation value and the horizontal axis indicates the AF signal.

[0070] Fig. 11 is a diagram showing plots of focus evaluation values ​​of each autofocus signal value of the evaluation board in embodiment 1. In Fig. 11, the vertical axis shows focus evaluation values, and the horizontal axis shows autofocus signal values. The example in Fig. 11 shows focus evaluation values ​​at six autofocus signal values ​​ε1, εi, εN. As autofocus signals are used, the graph is not symmetrical, resulting in nonlinear errors.

[0071] In the function approximation step (S124), the fitting processing unit 56 approximates the focus evaluation value for each plotted autofocus signal value with a convex polynomial function. As shown in the example of Fig. 11, the function obtained by approximating the AF signal and the focus evaluation value for each height position, and by which the focus evaluation value has a maximum value Cm when the AF signal value is εm, is used as correlation data.

[0072] In the above example, the case where an approximated function is used as the correlation data has been described, but the present invention is not limited to this. For example, it is also preferable to use a numerical sequence of the AF signal and the focus evaluation value for each height position as the correlation data.

[0073] The obtained correlation data is stored in the storage device 57. In this manner, the graph shape obtained from the correlation data for the evaluation board is used as a template for the board to be inspected.

[0074] In the inspection substrate carrying-in step (S202), the inspection substrate 101 carried from the autoloader 130 is placed on the XYθ table 102.

[0075] In the inspection target substrate height position setting and measurement step (S204), the height position of the XYθ table 102 is driven by the Z drive mechanism 132 under the control of the stage height control unit 62 to variably set the inspection target substrate height position (pattern formation surface height position). The inspection target substrate height position is measured by the position sensor 134. The inspection target 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.

[0076] A geometric pattern to be inspected is formed on the inspected substrate 101. For example, a line and space pattern or a hole pattern is formed.

[0077] In the light intensity measurement step (S206), with the height position of the inspected substrate controlled to height position hj, the light amount at the front focal position of light irradiated with the inspection light and transmitted through or reflected by the inspected substrate 101 is measured by the light amount sensor 185. Similarly, the light amount at the back focal position is measured by the light amount sensor 187. Specifically, the operation is as follows, where j indicates an index.

[0078] Laser light having a wavelength below the ultraviolet range (e.g., DUV light) that serves as inspection light is irradiated from an appropriate light source 103 to a beam splitter 174 by a reflective illumination optical system 171. The irradiated laser light is reflected by the beam splitter 174 and irradiated to the inspected substrate 101 by the magnifying optical system 104. The light reflected from the inspected substrate 101 passes through the magnifying optical system 104 and the beam splitter 174, and irradiates the beam splitter 177. The light split by the beam splitter 177 enters the autofocus optical system 180.

[0079] Light incident on the autofocus optical system 180 is refracted in the light-collecting direction by the imaging optical system 181, and irradiates the beam splitter 182. The light transmitted through the beam splitter 182 is partially restricted by a slit plate 184 at the front focal position (front focus position), and the amount of light passing through the slit plate 184 is measured by a light amount sensor 185. The light branched from the beam splitter 182 is partially restricted by a slit plate 186 at the back focal position (back focus position), and the amount of light passing through the slit plate 186 is measured by a light amount sensor 187. This makes it possible to measure the amount of light at the front focus position and the back focus position at the height position hj. The measured light amount data (light intensity data) of the light amount at the front focus position and the light amount at the back focus position at the height position hj is stored in the storage device 51.

[0080] In the autofocus signal calculation step (S208), the autofocus signal calculation unit 80 calculates an AF signal δj when the inspected substrate height position is height position hj. The AF signal δj is defined by the formula (4) using the light amount Aj at the front focal position and the light amount Bj at the back focal position, where j represents an index. (4) δj=(Aj-Bj) / (Aj+Bj)

[0081] The value of the AF signal δj is stored, for example, in the storage device 51 in association with the height position hj.

[0082] As an optical image acquisition step (S210), the optical image acquisition mechanism 150 places the inspected substrate 101 on the XYθ table 102, and captures an optical image of the inspected substrate 101 at a set height position hj by receiving light that is irradiated with inspection light and transmitted through or reflected from the inspected substrate 101 at the imaging sensor 105 via the inspection optical system 175.

[0083] The optical image acquisition mechanism 150 scans the inspection stripe 20 including the preset frame region 30 of the inspected substrate 101 with a laser beam (inspection beam) and captures an image of the stripe region with the imaging sensor 105. Specifically, it operates as follows. The XYθ table 102 is moved to a position where the inspection stripe 20 of the inspected substrate 101 can be imaged. In the transmission inspection, the pattern formed on the inspected substrate 101 is irradiated with a laser beam (e.g., DUV beam) having a wavelength of ultraviolet or less, which serves as inspection beam, from an appropriate light source 103 via the transmission illumination optical system 170. In other words, the transmission illumination optical system 170 illuminates the inspected substrate on which the pattern is formed. The light transmitted through the inspected substrate 101 is focused as an optical image by the imaging optical system 178 via the magnifying optical system 104 and the collimator lens 176 and is incident on the imaging sensor 105 (one example of a sensor).

[0084] Alternatively, in a reflection inspection, a laser light having a wavelength of ultraviolet or less (e.g., DUV light) serving as inspection light is irradiated from an appropriate light source 103 to a beam splitter 174 by a reflection illumination optical system 171. The irradiated laser light is reflected by the beam splitter 174 and irradiated to the substrate 101 by the magnifying optical system 104. The light reflected from the substrate 101 passes through the magnifying optical system 104, the beam splitter 174, and a collimator lens 176, and is focused as an optical image by the imaging optical system 178 on the imaging sensor 105, where it is incident.

[0085] The image sensor 105 captures an optical image of the substrate 101 to be inspected.

[0086] The pattern image formed on the image sensor 105 is photoelectrically converted by each photosensor element of the image sensor 105, and further A / D (analog-to-digital) converted by the sensor circuit 106. Then, pixel value data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (amount of light) of each pixel. Then, of the inspection stripe image, a frame image 31 (measurement image) of a preset frame area 30 is output to the autofocus control circuit 140 and stored in the storage device 61.

[0087] In the focus evaluation value calculation step (S212), the evaluation value calculation unit 82 calculates a focus evaluation value from the obtained image. For example, one of the contrast and brightness obtained from the optical image is used as the focus evaluation value. Here, the same focus evaluation value as that of the evaluation substrate is used. For example, contrast is used. As in the case described in FIG. 8, the contrast of the gradation data of each of the multiple lines in the direction (x direction) perpendicular to the direction in which the line pattern (or space pattern) extends (y direction) is calculated for the substrate 101 to be inspected. The contrast C can be defined by the formula (3) using the maximum and minimum values ​​of the gradation data.

[0088] Then, for example, the average value of the contrast of all the lines is calculated as the contrast of the image of the inspected substrate 101. Note that, in order to reduce measurement variation, it is desirable to use the average value of the contrast of as many lines as possible, but this is not limited to all the lines. As the pattern for which the average contrast is calculated, for example, it is sufficient to simply use a pattern of a size close to the evaluation pattern of the evaluation substrate that matches the performance of the inspection device 100.

[0089] Alternatively / and, when a hole pattern, which is another example of the pattern to be inspected, is captured in the measurement image, the contrast of the gradation data of each of a plurality of lines, for example, in the x direction perpendicular to the y direction, is calculated at a plurality of positions, for example, in the y direction, that overlap with the hole pattern, as in the case shown in Fig. 9. The contrast C can be defined by the above-mentioned formula (3) using the maximum and minimum values ​​of the gradation data.

[0090] Then, for example, the average value of the contrast of all the lines is calculated as the contrast of the image of the inspected substrate 101. The method of calculating the brightness is as described with reference to FIG.

[0091] Then, the process returns to the step of setting and measuring the height position of the substrate to be inspected (S204), and while changing the height position of the substrate to be inspected, each step from the step of setting and measuring the height position of the substrate to be inspected (S204) to the step of calculating the focus evaluation value (S212) is repeated. In this way, while varying the height position of the pattern formation surface of the substrate to be inspected 101, an optical image of the substrate to be inspected 101 is acquired for each height position. Also, 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 varying the height position of the pattern formation surface of the evaluation substrate on which the figure pattern is formed. Here, the AF signal and the focus evaluation value for each height position of the substrate to be inspected 101 are acquired at three or more different height positions hj, which is fewer than when the correlation data of the evaluation substrate is acquired.

[0092] As a measurement value plotting step (S220), the plot processing unit 84 plots the focus evaluation value of each acquired AF signal value in a coordinate system in which the vertical axis indicates the focus evaluation value and the horizontal axis indicates the AF signal.

[0093] Fig. 12 is a diagram showing plots of focus evaluation values ​​of each autofocus signal value of an inspected substrate in embodiment 1. In Fig. 12, the vertical axis represents focus evaluation value, and the horizontal axis represents autofocus signal value. In the example of Fig. 12, focus evaluation values ​​at three autofocus signal values ​​δj are shown.

[0094] Here, the AF signal value indicating the height of the substrate to be inspected changes with the temperature change of the apparatus, and the contrast evaluation value is affected by the phase change of the substrate to be inspected, etc., so the combination of the AF signal and focus evaluation value obtained on the substrate to be inspected 101 does not necessarily match the numerical value of the combination of the AF signal and focus evaluation value on the evaluation substrate. However, the line width size of the geometric pattern to be inspected formed on the substrate to be inspected 101 is generally formed to a size that matches the performance of the inspection apparatus 100. Therefore, it shows a behavior similar to that of the evaluation pattern.

[0095] In the inspection autofocus signal calculation step (S222), the inspection autofocus signal calculation unit 86 calculates an inspection AF signal δm that provides a focus evaluation value equal to or greater than a threshold value in the inspected substrate 101, using the AF signal and focus evaluation value acquired for each height position while varying the height position of the pattern formation surface of the inspected substrate 101 with the substrate 101 on which a geometric pattern is formed placed on the XYθ table 102 (stage), and correlation data on the evaluation substrate. A specific description will now be given.

[0096] 12, a graph shape (template) indicated by the correlation data is applied to the plotted results for the inspected substrate 101. The template indicated by the correlation data is applied so that multiple combinations of the AF signals and focus evaluation values ​​obtained from the plotted inspected substrate 101 are positioned on the graph indicated by the correlation data. Then, the inspection autofocus signal calculation unit 86 calculates an AF signal δm in which the focus evaluation value is equal to or greater than the threshold value Thf in the graph to which the template is fitted. The threshold value Thf is preferably set to, for example, 90% or more of the maximum value Cm' of the fitted template. More preferably, the inspection autofocus signal calculation unit 86 calculates an AF signal δm that is the maximum value Cm' of the fitted template. In this way, the inspection AF signal δm on the substrate 101 to be inspected can be obtained. The value of the inspection AF signal δm is stored in, for example, the storage device 51.

[0097] In the image acquisition (autofocus control) step (S250), the optical image acquisition mechanism 150 adjusts the height position of the pattern-formed surface of the inspected substrate 101 to a height position of the pattern-formed surface corresponding to the value of the inspection autofocus signal δm, while receiving light irradiated with inspection light and transmitted through or reflected from the substrate 101 at the imaging sensor 105 via the inspection optical system 175, thereby capturing an optical image of the substrate 101. Specifically, the operation is as follows.

[0098] The optical image acquisition mechanism 150 scans the inspection stripes 20 of the inspected substrate 101 with a laser beam (inspection beam) and captures a stripe region image for each inspection stripe 20 by the imaging sensor 105. Specifically, it operates as follows. The XYθ table 102 is moved to a position where the target inspection stripe 20 can be imaged. In the transmission inspection, a laser beam (e.g., DUV beam) having a wavelength of ultraviolet or less, which serves as inspection beam, is irradiated onto the pattern formed on the substrate 101 from an appropriate light source 103 via the transmission illumination optical system 170. In other words, the transmission illumination optical system 170 illuminates the inspected substrate 101 on which the pattern is formed. The light transmitted through the inspected substrate 101 is focused as an optical image by the imaging optical system 178 via the magnifying optical system 104 and the collimator lens 176 on the imaging sensor 105 (one example of a sensor), and is incident thereon.

[0099] Alternatively, in a reflection inspection, a laser light having a wavelength of ultraviolet or less (e.g., DUV light) serving as inspection light is irradiated from an appropriate light source 103 to a beam splitter 174 via a reflection illumination optical system 171 onto a pattern formed on the substrate 101 to be inspected. The irradiated laser light is reflected by the beam splitter 174 and irradiated onto the sample 101 via the magnifying optical system 104. The light reflected from the sample 101 passes through the magnifying optical system 104, the beam splitter 174, and the collimator lens 176, and is focused as an optical image by the imaging optical system 178 onto the imaging sensor 105, where it is incident.

[0100] When capturing such an optical image, the autofocus mechanism 131 adjusts the height position of the pattern-formed surface of the substrate 101 to a height position hm of the pattern-formed surface corresponding to the value δm of the AF signal for inspection. In other words, the autofocus mechanism 131 adjusts the height position of the pattern-formed surface of the substrate 101, which may vary with the horizontal movement of the XYθ table 102, to a height position hm corresponding to the autofocus signal for inspection δm, while the substrate 101 is placed on the XYθ table 102. Specifically, the autofocus processing unit 66 inputs the light amounts at the front focus position and the back focus position from the light amount sensors 185 and 187, and calculates the AF signal z. Then, the Z drive mechanism 132 is controlled so that the AF signal z becomes δm.

[0101] Alternatively, it is also suitable to control using an offset. In this case, offset calculation unit 88 calculates a difference obtained by subtracting zero from inspection AF signal Δm as offset value z0. Then, autofocus processing unit 66 inputs the light amount at the front focus position and the light amount at the back focus position from light amount sensors 185, 187, and calculates AF signal z. Then, autofocus processing unit 66 outputs a value obtained by subtracting offset value z0 from the calculated AF signal z to Z driving mechanism 132. Z driving mechanism 132 adjusts the mask surface height position so that the value obtained by subtracting offset value z0 from the calculated AF signal z becomes zero.

[0102] The image sensor 105 captures an optical image of the substrate 101 by receiving light that is irradiated with the inspection light and transmitted through or reflected from the substrate 101, while the height position of the pattern-formed surface of the substrate 101 is adjusted to a height position of the pattern-formed surface corresponding to the value of the inspection AF signal δm.

[0103] The pattern image formed on the image sensor 105 is photoelectrically converted by each photosensor element of the image sensor 105, and further A / D (analog-to-digital) converted by the sensor circuit 106. Then, pixel value data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light amount) of each pixel.

[0104] Meanwhile, the reference image creation circuit 112 uses the graphic pattern data (design data) to create a reference image that serves as a reference. The creation of the reference image is performed for each inspection stripe 20 of the inspected substrate 101 in parallel with the scanning operation of the inspection stripe 20. More specifically, the operation is as follows. The reference image creation circuit 112 inputs graphic pattern data (design data) for each frame area 30 of the target inspection stripe 20, and converts each graphic pattern defined in the graphic pattern data into binary or multi-value image data.

[0105] The figures defined in the graphic pattern data are, for example, rectangles and triangles as basic figures, and graphic data is stored that defines the shape, size, position, etc. of each pattern figure using information such as the coordinates (x, y) at the reference position of the figure, the length of the sides, and a graphic code that serves as an identifier to distinguish the type of figure, such as a rectangle or triangle.

[0106] When the design pattern data that becomes such graphic data is input to the reference image creation circuit 112, it is expanded into data for each graphic, and the graphic code indicating the graphic shape of the graphic data, the graphic dimensions, etc. are interpreted. Then, it is expanded into binary or multi-value design pattern image data as a pattern to be placed within a grid with a predetermined quantized dimension as a unit, and output. In other words, the design data is read, the frame area is virtually divided into grids with a predetermined dimension as a unit, the occupancy rate of the graphic in the design pattern is calculated for each grid, and n-bit occupancy data (design image data) is output. For example, it is preferable to set one grid as one pixel. Then, 1 / 2 pixel is assigned to one pixel. 8If a pixel has a resolution of (=1 / 256), a small area of ​​1 / 256 is allocated for the area of ​​the figure placed within the pixel to calculate the occupancy rate within the pixel. This is then created as 8-bit occupancy data. The grid (inspection pixels) can be aligned with the pixels of the measurement data.

[0107] Next, the reference image creation circuit 112 performs filtering using a filter function on the design image data of the design pattern, which is image data of the graphic.

[0108] FIG. 13 is a diagram for explaining the filter processing in the first embodiment. The pixel data of the optical image captured from the inspected substrate 101 is in a state where a filter is applied due to the resolution characteristics of the optical system used for capturing the image, in other words, in an analog state where the pixel data is continuously changing, and therefore, for example, as shown in FIG. 13, the pixel data is different from the developed image (design image) in which the image intensity (gray value) is a digital value. On the other hand, as described above, the figure pattern data is defined by the figure code, and therefore the image intensity (gray value) may be a digital value in the developed design image. Therefore, the reference image creation circuit 112 creates a reference image that is close to the optical image by performing image processing (filter processing) on ​​the developed image. This allows the design image data, which is the image data on the design side in which the image intensity (gray value) is a digital value, to be matched to the image generation characteristics of the measurement data (optical image). The created reference image is output to the comparison circuit 108.

[0109] FIG. 14 is a diagram showing an example of the internal configuration of the comparison circuit in the first embodiment. In FIG. 14, the comparison circuit 108 includes storage devices 70, 72, 76 such as magnetic disk devices, a frame image creation unit 74, a positioning unit 78, and a comparison processing unit 79. A series of "units" such as the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 have processing circuits. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. In addition, each "unit" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. Input data or calculation results required for the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 are stored in a memory (not shown) in the comparison circuit 108 or in a memory 111 each time.

[0110] The stripe data (stripe area 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.

[0111] In the comparison step (S252), the comparison circuit 108 (an example of a comparison unit) uses a reference image to compare the captured optical pixels with the reference image and outputs the result. Specifically, the operation is as follows.

[0112] In the comparison circuit 108, first, the frame image creation unit 74 generates a plurality of frame images 31 by dividing the stripe region image (optical image) at a predetermined width. Specifically, as shown in FIG. 2, the stripe region image is divided into frame images of a plurality of rectangular frame regions 30. For example, the image is divided into frames of 512×512 pixels. Data of each frame region 30 is stored in the storage device 76.

[0113] Next, the alignment unit 78 reads out the corresponding frame image 31 and the corresponding reference image for each frame region 30 from the storage devices 72 and 76, and aligns the frame image 31 with the corresponding reference image using a predetermined algorithm. For example, the alignment is performed using the least squares method.

[0114] Then, the comparison processing section 79 (another example of a comparison section) compares the frame image 31 with a reference image corresponding to the frame image 31. For example, it compares them pixel by pixel. Here, the two are compared pixel by pixel according to a predetermined judgment condition to judge the presence or absence of a defect such as a shape defect. The judgment condition may be, for example, to compare the two pixel by pixel according to a predetermined algorithm to judge the presence or absence of a defect. For example, the difference value between the pixel values ​​of both images is calculated pixel by pixel, and if the difference value is greater than a threshold value Th, it is judged to be a defect. The comparison result may be output to, for example, the magnetic disk device 109, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, or may be output from the printer 119.

[0115] In the above example, the case of die-database inspection has been described, but die-die inspection may also be performed. In this case, the comparison circuit 108 uses the frame image (optical image) of the die 2 acquired for one of the frame areas 30 for which the die-die inspection is performed as a reference (reference image). First, the alignment unit 78 reads out the frame image 31 of the die 1 and the frame image of the die 2 corresponding to each frame area 30 for which the die-die inspection is performed from the storage device 76, and aligns the frame image 31 of the die 1 and the frame image of the die 2 using a predetermined algorithm. For example, the alignment is performed using the least squares method. Then, the comparison processing unit 79 (comparison unit) compares the frame image 31 of the die 1 and the frame image of the die 2 corresponding to each frame area 30 for which the die-die inspection is performed, pixel by pixel.

[0116] As described above, according to the first embodiment, the parameters required for the autofocus operation of the inspected substrate 101 can be acquired in a shorter time than in the past. Conventionally, in order to precisely calculate the AF signal that maximizes the focus evaluation value, it was necessary to perform "changes in focus evaluation value relative to changes in AF signal" at many sample points (10 or more). On the other hand, according to the first embodiment, the template creation process using the evaluation board shown in FIG. 11 only needs to be performed once at the start-up of the device (not included in the inspection time), so it is possible to precisely acquire a template curve after collecting many sample points (10 or more, no time limit). When inspecting the board to be inspected, it is sufficient to collect, for example, three sample points as the minimum required and apply them to the template. Therefore, according to the first embodiment, the time required for the process to acquire parameters required for autofocus operation can be reduced to, for example, 3 / 10=30%. It can be further reduced depending on the number of measurement points.

[0117] Although the embodiments have been described above with reference to specific examples, the present invention is not limited to these specific examples.

[0118] In addition, although the description of the device configuration, control method, and other parts that are not directly necessary for the explanation of the present invention are omitted, the required device configuration and control method can be appropriately selected and used. For example, although the description of the control unit configuration that controls the inspection device 100 is omitted, it goes without saying that the required control unit configuration can be appropriately selected and used.

[0119] In addition, all pattern inspection apparatuses, focal position adjustment methods, and pattern inspection methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention. [Explanation of symbols]

[0120] 20 Inspection Stripes 30 Frame Area 31 Frame Images 50 Autofocus signal calculation unit 51,57,61 Storage device 52 Evaluation value calculation unit 53 Correlation Data Creation Department 54 Plot processing section 56 Fitting processing section 62 Stage height control section 64 Autofocus signal calculation unit 66 Autofocus processing unit 70,71,72,76 Storage device 74 Frame image generator 78 Alignment section 79 Comparison processing section 80 Autofocus signal calculation unit 82 Evaluation value calculation unit 84 Plot processing section 86 Inspection autofocus signal calculation unit 88 Offset calculation unit 100 Inspection Equipment 101 Tested board 102 XYθ table 103 Light source 104 Magnifying Optical System 105 Image Sensor 106 Sensor Circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk device 110 Control computer 111 Memory 112 Reference image creation circuit 113 Autoloader control circuit 114 Table control circuit 115 Magnetic Tape Unit 116FD 117CR 118 Pattern Monitor 119 Printer 120 Bus 122 Laser length measurement system 123 Stripe Pattern Memory 130 Autoloader 131 Autofocus mechanism 132 Z drive mechanism 134 Position Sensor 140 Autofocus control circuit 150 Optical image acquisition mechanism 160 Control Circuits 170 Transmitted illumination optical system 171 Reflected illumination optical system 174 Beam splitter 175 Inspection Optical System 176 Collimator Lens 177 Beam splitter 178 Imaging Optical System 180 Autofocus Optical System 181 Imaging Optical System 182 Beam splitter 184,186 Slit plate 185,187 Light sensor

Claims

1. A stage on which a substrate is placed; A drive mechanism for moving the height position of the stage; a correlation data creation unit that creates correlation data between an autofocus signal used as a parameter for autofocus control and a focus evaluation value for evaluating a focus position, the autofocus signal being acquired for each height position while varying the height position of a pattern formation surface of an evaluation substrate on which an evaluation pattern has been formed, with the evaluation substrate placed on the stage; and A storage device that stores the correlation data; an inspection autofocus signal calculation unit that calculates an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using the autofocus signal and the focus evaluation value acquired for each height position while varying the height position of the pattern formation surface of the substrate to be inspected in a state where the substrate to be inspected, on which a geometric pattern is formed, is placed on the stage, and the correlation data on the evaluation substrate; an autofocus mechanism that adjusts the height position of the pattern-formed surface of the substrate to a height position of the pattern-formed surface that corresponds to the value of the inspection autofocus signal; a sensor that captures an optical image of the substrate to be inspected by receiving light that is irradiated with an inspection light and transmitted through or reflected from the substrate to be inspected, in a state in which the height position of the pattern-formed surface of the substrate to be inspected is adjusted to a height position of the pattern-formed surface that corresponds to the value of the inspection autofocus signal; a comparison unit for comparing the captured optical pixels with a reference image using the reference image; A pattern inspection device comprising:

2. 2. The pattern inspection apparatus according to claim 1, wherein a function obtained by approximating the autofocus signal and the focus evaluation value for each height position is used as the correlation data.

3. 2. The pattern inspection apparatus according to claim 1, wherein a sequence of values ​​of the autofocus signal and the focus evaluation value for each height position is used as the correlation data.

4. 4. The pattern inspection device according to claim 1, wherein the autofocus signal and the focus evaluation value for each height position on the inspected substrate are obtained at three or more different height positions.

5. a step of creating correlation data between the autofocus signal and the focus evaluation value, the autofocus signal being used as a parameter for autofocus control and the focus evaluation value for evaluating the focus position, acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate with the evaluation pattern formed thereon, in a state in which the evaluation substrate is placed on a stage; storing the correlation data in a storage device; a step of calculating an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using the autofocus signal and the focus evaluation value acquired for each height position while varying the height position of the pattern formation surface of the substrate to be inspected in a state where the substrate to be inspected has a graphic pattern formed thereon and the correlation data on the evaluation substrate; a step of adjusting a height position of a pattern-formed surface of the substrate to a height position of the pattern-formed surface corresponding to a value of the inspection autofocus signal when an optical image of the substrate is captured by a sensor by receiving light that is irradiated with an inspection light and transmitted through or reflected by the substrate; A focus position adjusting method comprising:

6. a step of creating correlation data between the autofocus signal and the focus evaluation value, the autofocus signal being used as a parameter for autofocus control and the focus evaluation value for evaluating the focus position, acquired for each height position while varying the height position of the pattern formation surface of the evaluation substrate with the evaluation pattern formed thereon, in a state in which the evaluation substrate is placed on a stage; storing the correlation data in a storage device; a step of calculating an inspection autofocus signal that provides a focus evaluation value equal to or greater than a threshold value on the substrate to be inspected, using the autofocus signal and the focus evaluation value acquired for each height position while varying the height position of the pattern formation surface of the substrate to be inspected in a state where the substrate to be inspected has a graphic pattern formed thereon and the correlation data on the evaluation substrate; a step of capturing an optical image of the substrate to be inspected by a sensor by receiving light irradiated with an inspection light and transmitted through or reflected from the substrate to be inspected while adjusting a height position of the pattern-formed surface of the substrate to a height position of the pattern-formed surface corresponding to the value of the inspection autofocus signal; using a reference image to compare the captured optical pixels with the reference image and outputting the result; A pattern inspection method comprising:

Images