Inspection device, inspection method, and method for acquiring offset amount

Abstract

To increase detection accuracy in the entire field of view of an optical microscope including a field of view peripheral part, in inspection of a pattern provided on a substrate.SOLUTION: An inspection device 10 inspects a pattern provided on a substrate. The inspection device 10 has an optical microscope 11 that acquires an image of the pattern, and an inspection unit 12 that conducts inspection on the basis of the image. The optical microscope 11 has a focus position adjustment unit 24 that sets a position offset from a just focus position relative to the substrate as an inspection focus position for the inspection. The inspection unit 12 conducts the inspection on the basis of an image acquired at the inspection focus position.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The presently disclosed invention relates to an inspection apparatus for inspecting a pattern provided on a substrate, an inspection method for inspecting a pattern provided on a substrate, and a method for acquiring an offset amount used in the inspection apparatus and the inspection method. [Background technology]

[0002] A semiconductor wafer has a large number of chips arranged in a matrix, and each chip has a circuit pattern. An inspection (visual inspection) is performed to check whether a predetermined pattern is formed on such a semiconductor wafer. Patent Document 1 discloses an apparatus for performing such an inspection. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2023-142887 Summary of the Invention [Problem to be solved by the invention]

[0004] In the inspection, the presence or absence of defects such as foreign matter contained in the pattern, chipping of the pattern, peeling of the pattern, etc. For the inspection, an optical microscope is used, and the acquired image is processed to make a pass / fail judgment based on, for example, brightness values. The above-described defect inspection is performed not only on semiconductor wafers but also on photomasks or substrates such as printed circuit boards.

[0005] In the case of an optical microscope, the most focused position in the center of the inspection field (i.e., the just-focus position) is conventionally set as the inspection focus position, and an image is acquired. Pass / fail judgment is made based on that image. However, in this case, due to the characteristics of the objective lens of the optical microscope, the pattern corresponding to the peripheral part of the inspection field of view is not in focus, which may result in a decrease in the inspection accuracy of the pattern corresponding to the peripheral part of the field of view.

[0006] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to improve the inspection accuracy of patterns formed on a substrate over the entire field of view of an optical microscope, including the peripheral areas. [Means for solving the problem]

[0007] An inspection device inspects a pattern provided on a substrate. The inspection device includes an optical microscope that acquires an image of the pattern and an inspection unit that performs inspection based on the image. The optical microscope has a focus position adjustment unit that sets a position offset from a just focus position for the substrate as an inspection focus position for inspection, and the inspection unit performs inspection based on the image acquired at the inspection focus position.

[0008] An inspection method for inspecting a pattern provided on a substrate includes a focus position adjusting step of adjusting an inspection focus position for inspection using an optical microscope, an image acquiring step of acquiring an image of the pattern at the inspection focus position, and an inspection step of performing inspection based on the image. In the focus position adjusting step, a position offset from a just focus position for the substrate is set as the inspection focus position, and in the inspection step, inspection is performed based on the image acquired at the inspection focus position.

[0009] The offset amount acquisition method is a method for acquiring an offset amount to be offset from an just-focus position of an optical microscope in order to set an inspection focus position of the optical microscope relative to a substrate. The offset amount acquisition method includes an imaging step in which the optical microscope acquires an image of the substrate through an objective lens, a parameter acquisition step in which image parameters of the image acquired by the optical microscope are acquired, and an offset amount acquisition step in which the offset amount corresponding to the objective lens is acquired based on the image parameters. In the imaging step, images of the substrate are acquired while changing the focus position of the optical microscope, and in the parameter acquisition step, the image parameters of the image acquired by the optical microscope at each of the changed focus positions are acquired, and in the offset amount acquisition step, the offset amount is acquired based on statistics of the image parameters of a central portion of the image and the image parameters of a peripheral portion of the image at each of the changed focus positions. [Effects of the Invention]

[0010] According to the present invention, it is possible to improve the inspection accuracy in the entire field of view of an optical microscope, including the peripheral area, when inspecting a pattern provided on a substrate. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a configuration diagram showing an embodiment of an inspection device according to the present invention. [Figure 2] FIG. 2 is an explanatory diagram of the inspection field of an optical microscope. [Figure 3] FIG. 3 is a graph showing MTF values at various positions in the test field of view of FIG. [Figure 4] FIG. 4 is a graph showing the MTF values at each position in the test field of view of FIG. [Figure 5] FIG. 5 is an explanatory diagram of a mechanism for determining the just-focus position. [Figure 6] FIG. 6 is a flow diagram showing the inspection method. [Figure 7]FIG. 7 is a flowchart showing a method for obtaining the offset amount. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Outline of the embodiment of the present invention> Hereinafter, an outline of an embodiment of the present invention will be listed and described. (1) The inspection device of the present invention inspects a pattern provided on a substrate. The inspection device includes an optical microscope that acquires an image of the pattern and an inspection unit that performs inspection based on the image. The optical microscope has a focus position adjustment unit that sets a position offset from a just-in-focus position for the substrate as an inspection focus position for inspection, and the inspection unit performs inspection based on the image acquired at the inspection focus position.

[0013] When the focus position of an optical microscope is set to the just-in-focus position, it is often the case that the pattern corresponding to the peripheral portion of the field of view is not in focus. Even in such cases, the inspection device described above makes it possible to increase the MTF (Modulation Transfer Function) value in the peripheral portion of the field of view. As a result, the average MTF value over the entire field of view can be increased, making it possible to improve inspection accuracy not only in the central portion of the field of view but also throughout the entire field of view, including the peripheral portion. The just-in-focus position is the focus position at which the MTF value is highest in the center of the inspection field of the optical microscope. The inspection focus position is the focus position when an inspection is actually performed.

[0014] (2) The inspection device of (1) has a focus control unit that determines the just-in-focus position for the substrate, and the optical microscope has an objective lens, a stage on which the substrate is placed, and a moving mechanism that moves the objective lens and the stage relative to each other, and the focus position adjustment unit sets a position offset from the just-in-focus position as the inspection focus position. While the stage carrying the workpiece and the objective lens move relative to each other, a position offset from the just-focus position is set as the inspection focus position, and images are acquired, which shortens the time required for inspection.

[0015] (3) Alternatively, the inspection device of (1) has a focus control unit that determines the just focus position for the substrate, and the optical microscope has an objective lens, a stage on which the substrate is placed, and a moving mechanism that performs relative movement between the objective lens and the stage, and while the moving mechanism temporarily stops the relative movement, the focus control unit obtains the just focus position, and the focus position adjustment unit sets a position offset from the just focus position as the inspection focus position. The stage on which the workpiece is placed and the objective lens move relatively, and with the relative movement temporarily stopped, a position offset from the just focus position is set as the inspection focus position, and inspection is then performed.

[0016] (4) The inspection device of (1) to (3) has a memory unit that stores correspondence information indicating the relationship between an objective lens and data regarding an offset amount, and a focus control unit that acquires data regarding the offset amount from the objective lens to be used and the correspondence information, and the focus position adjustment unit sets a position offset from the just focus position by the offset amount as the inspection focus position. According to the above configuration, the focus control unit acquires data on the offset amount from the objective lens used for inspection and the corresponding information stored in advance in the storage unit, making it easier to set the offset amount and improving inspection efficiency.

[0017] (5) In the inspection device of (4), the optical microscope has a plurality of objective lenses, and the storage unit stores the correspondence information for each of the plurality of objective lenses. According to the above configuration, even if the characteristics of each objective lens are different, the offset amount is set for each objective lens.

[0018] (6) An inspection method of the present invention inspects a pattern provided on a substrate, and includes a focus position adjusting step of adjusting an inspection focus position for inspection using an optical microscope, an image acquiring step of acquiring an image of the pattern at the inspection focus position, and an inspection step of performing inspection based on the image, wherein the focus position adjusting step sets the inspection focus position to a position offset from a just focus position for the substrate, and the inspection step performs inspection based on the image acquired at the inspection focus position.

[0019] When the focus position of an optical microscope is set to the just-in-focus position, it is often the case that the pattern corresponding to the peripheral portion of the field of view is not in focus. Even in such cases, the inspection method described above makes it possible to increase the MTF (Modulation Transfer Function) value in the peripheral portion of the field of view. As a result, the average MTF value over the entire field of view can be increased, thereby improving inspection accuracy not only in the central portion of the field of view but also throughout the entire field of view, including the peripheral portion.

[0020] (7) A method for acquiring an offset amount according to the present invention is a method for acquiring an offset amount to be offset from an just-focus position of an optical microscope in order to set an inspection focus position of the optical microscope relative to a substrate. The offset amount acquisition method includes a photographing step in which the optical microscope acquires an image of the substrate through an objective lens, a parameter acquisition step in which image parameters of the image acquired by the optical microscope are acquired, and an offset amount acquisition step in which the offset amount corresponding to the objective lens is acquired based on the image parameters. In the photographing step, images of the substrate are acquired while changing the focus position of the optical microscope, and in the parameter acquisition step, the image parameters of the image acquired by the optical microscope at each of the changed focus positions are acquired. In the offset amount acquisition step, the offset amount is acquired based on statistics of the image parameters of a central portion of the image and the image parameters of a peripheral portion of the image at each of the changed focus positions.

[0021] According to the acquisition method, a position offset by a predetermined offset amount from the just focus position of the optical microscope with respect to the substrate is set as the inspection focus position, and the offset amount is acquired.

[0022] <Details of the embodiment of the present invention> Hereinafter, the details of the embodiments of the present invention will be described. FIG. 1 is a configuration diagram showing one embodiment of an inspection apparatus of the present invention. The inspection apparatus 10 shown in FIG. 1 is an apparatus for inspecting a pattern provided on a substrate. In this embodiment, the substrate is a semiconductor wafer W (hereinafter referred to as "wafer W"). The wafer W has a large number of chips C arranged in a matrix, and each chip C has a circuit pattern (hereinafter referred to as "pattern").

[0023] The inspection apparatus 10 inspects such a wafer W. That is, the inspection apparatus 10 acquires an image of the pattern of the chips C provided on the wafer W and performs an inspection (visual inspection) to determine whether or not a predetermined pattern is formed on the wafer W (each chip C). To this end, the inspection apparatus 10 has an optical microscope 11 and an inspection unit 12. The inspection apparatus 10 of this embodiment further has a processing unit 13, a focus control unit 14, and a memory unit 15.

[0024] The optical microscope 11 includes an objective lens 21, a stage 22, a moving mechanism 23, a focus position adjusting unit 24, an imaging device 25, and a microscope body 26 that supports these components. The stage 22 carries the wafer W to be inspected. The optical microscope 11 of this embodiment has a revolver 27, and in order to change the magnification, the revolver 27 is equipped with a plurality of objective lenses 21. The objective lenses 21 are positioned above a stage 22, and the observation direction by the optical microscope 11 is the up-down direction.

[0025] The movement mechanism 23 is a device for relatively moving the objective lens 21 and the stage 22 so that the entire surface of the wafer W can be inspected. In the embodiment shown in Fig. 1, the movement mechanism 23 moves the stage 22 relative to the objective lens 21. The direction of the relative movement is a direction (horizontal direction) perpendicular to the up-down direction, which is the observation direction, and the stage 22 is movable in two perpendicular axial directions. 1, the direction in which the objective lens 21 faces the workpiece W on the stage 22 (the observation direction) is shown as the Z-axis direction. The directions of the relative movement by the movement mechanism 23 are shown as the X-axis direction and the Y-axis direction.

[0026] The photographing device 25 is a camera (for example, a CCD camera) and captures an image of the chip C. The photographing device 25 has an image sensor (image pickup element) 252. The optical microscope 11 of this embodiment further includes a condenser lens and an illuminator, both of which are not shown. The illuminator emits light. The light is condensed by the condenser lens and irradiated onto the surface of the wafer W along the optical axis of the objective lens 21. The light reflected from the wafer W passes through the objective lens 21 and enters the image sensor 252.

[0027] With the above configuration, the photographing device 25 acquires an image of the pattern of the chips C provided on the wafer W. The image acquired by the photographing device 25 is provided to the processing unit 13, which then processes the image. By changing the magnification, multiple chips C can be placed in one field of view of the optical microscope 11 and an image can be obtained, or one chip C can be placed in the same field of view and an image can be obtained, or a portion of one chip C can be placed in the same field of view and an image can be obtained.

[0028] The processing unit 13 is configured to have an arithmetic processing device (computer) that performs arithmetic processing. The processing unit 13 can process images acquired by the imaging device 25 using the functions of the arithmetic processing device. Data resulting from the image processing by the processing unit 13 is provided to the inspection unit 12.

[0029] The focus position adjustment unit 24 of the optical microscope 11 is an adjustment mechanism that adjusts the distance between the wafer W on the stage 22 and the objective lens 21. The focus position adjustment unit 24 adjusts the distance in the vertical direction, which is the observation direction. The focus position adjustment unit 24 is configured to have an actuator (not shown) including an electric motor (servo motor), and adjusts the distance electrically. The focus position adjustment unit 24 may be configured to move the objective lens 21 (microscope main body 26) relative to the stage 22, or may be configured to move the stage 22 relative to the objective lens 21 (microscope main body 26).

[0030] The focus position adjusting unit 24 changes and adjusts the focus position of the optical microscope 11 with respect to the wafer W. The operation of the focus position adjusting unit 24, that is, the operation of the electric motor, is controlled by the focus control unit 14. As will be explained later, the focus position adjusting unit 24 sets a position offset from the just focus position for the wafer W as the inspection focus position for inspection.

[0031] The amount by which the focus position is offset from the just-focus position is called the "offset amount." The focus position adjustment unit 24 offsets the just-focus position by a preset offset amount in order to acquire an image. The offset position is set as the inspection focus position for inspection.

[0032] The just-focus position is a focus position at the center of the inspection field of the optical microscope 11 where the MTF (Modulation Transfer Function) value is the highest. The inspection focus position is the focus position when an inspection is actually performed. That is, the focus position of the optical microscope 11 that acquires an image of the wafer W for inspection by the inspection unit 12 is the inspection focus position.

[0033] The memory unit 15 is a storage device formed of a semiconductor memory, a hard disk, or the like. The memory unit 15 stores correspondence information K indicating the relationship between the objective lens 21 and the data related to the offset amount. The optical microscope 11 of this embodiment has multiple objective lenses 21 to obtain different magnifications. The memory unit 15 stores correspondence information K for each of the multiple objective lenses 21. The "data related to the offset amount" may be data of a value indicating the offset amount itself, or may be data equivalent to the offset amount (data obtained by converting the offset amount).

[0034] The focus control unit 14 is configured to include an arithmetic processing device (computer) that performs arithmetic processing. The focus control unit 14 has a function of determining the just focus position for the wafer W. The focus control unit 14 further has a function of obtaining data regarding the offset amount from the objective lens 21 used for inspection and the correspondence information K in the storage unit 15. A signal corresponding to the data relating to the acquired offset amount is given to the focus position adjustment unit 24. The focus position adjustment unit 24 sets a position offset from the just focus position for that offset amount as the inspection focus position for inspection.

[0035] The means for determining the just focus position and the method for obtaining the offset amount (corresponding information K) will be described later.

[0036] The inspection unit 12 is configured with an arithmetic processing device (computer) that performs arithmetic processing. The inspection unit 12 performs inspection processing based on images acquired by the imaging device 25. Specifically, the inspection unit 12 acquires the image processing results from the processing unit 13, and inspects the pattern defects of the wafer W (chip C) that is the inspection target based on the image processing results. The inspection unit 12 performs inspection based on images acquired at an inspection focus position that is offset from the just focus position as described above.

[0037] [Inspection field of the optical microscope 11] 2 is an explanatory diagram of the inspection field P of the optical microscope 11. The inspection field P coincides with the image acquired by the image capturing device 25. The image sensor 252 (FIG. 1) of the photographing device 25 includes a large number of pixels and obtains image data from the large number of pixels. Upon obtaining the image data, the processing unit 13 can calculate the luminance value of a predetermined pixel and image parameters such as the MTF (Modulation Transfer Function) at each position. The examination visual field P is composed of a central visual field portion P1 and a peripheral visual field portion P2 surrounding the central visual field portion P1. In Fig. 2, the boundary between the central visual field portion P1 and the peripheral visual field portion P2 is formally indicated by a virtual line (two-dot chain line) N.

[0038] Fig. 3 is a graph showing MTF values (measured values) at various positions in the examination visual field P of Fig. 2. Fig. 3 shows MTF measurement values at multiple positions on a dashed line L1 extending from the upper left to the lower right of the examination visual field P shown in Fig. 2. In the graph of FIG. 3, the dashed line connects the MTF values at each position when the position at which just focus is achieved in the central part P1 of the visual field (hereinafter referred to as "first case") is the focus position. In the first case, the MTF value is highest in the central part P1 of the visual field, whereas in the peripheral part P2 of the visual field, the MTF value gradually decreases toward the edge.

[0039] In the graph of Figure 3, a solid line connects the MTF values at each position when the focus position is a position offset by a predetermined offset amount from the position where the focus is just in focus at the center P1 of the field of view (hereinafter referred to as the "second case"). In the second case, compared to the first case, the MTF value is slightly lower in the central part P1 of the visual field, but in the peripheral part P2 of the visual field, the MTF value is partially highest and gradually decreases from that highest position toward the edge.

[0040] The average MTF value for the entire test visual field P is higher in the second case than in the first case.

[0041] FIG. 4 is a graph showing the MTF values (measured values) at each position in the examination visual field P of FIG. 2, and shows the MTF measurement values at multiple positions on the dashed dotted line L2 extending from the lower left to the upper right of the examination visual field P shown in FIG. 2. In Figure 4, in the second case shown by the solid line, the MTF value is slightly lower in the central part P1 of the visual field compared to the first case shown by the dashed line, but in the peripheral part P2 of the visual field, the MTF value is highest in that part and gradually decreases from that highest position toward the edge. As in the case of FIG. 3, the average value of the MTF over the entire test visual field P is higher in the second case than in the first case.

[0042] As described above, when a position offset from the just focus position for the wafer W is set as the inspection focus position (second case), the MTF value in the peripheral part P2 of the field of view becomes high, and as a result, it becomes possible to increase the average value of the MTF value throughout the entire inspection field of view P.

[0043] [Means for determining just-focus position] The just focus position for the wafer W is determined by the focus control unit 14. In order for the focus control unit 14 to determine the just focus position, the optical microscope 11 (see FIG. 5) has an optical detection system including an illuminator 29, a mirror 30, a half mirror 31, a beam splitter 32, an optical path difference prism 33, and two line sensors 34. These are mounted on the microscope body 26. FIG. 5 is an explanatory diagram of the mechanism for determining the just focus position.

[0044] A focus pattern is projected onto the wafer W by light from the illuminator 29. The focus pattern captured by the objective lens 21 enters the optical path difference prism 33 through the beam splitter 32. The focus pattern is split into two optical paths by the optical path difference prism 33. Two line sensors 34 receive the images (focus patterns) from the two optical paths, respectively. The signal of the image that is farther from the optical path difference prism 33 is defined as the Ach signal, and the signal of the image that is nearer from the optical path difference prism 33 is defined as the Bch signal. The optical detection system of the line sensor shown in Figure 5 is configured so that the position where the Ach signal and the Bch signal are equal is the focus.

[0045] The focus control unit 14 performs high-speed signal processing such as contrast detection on the Ach signal and Bch signal obtained by the two line sensors 34. The focus position adjustment unit 24 sets the focus distance of the optical microscope 11 to the position where the two signals are most similar. The focus distance is the distance between the wafer W on the stage 22 and the objective lens 21, and the relative position of the wafer W on the stage 22 and the objective lens 21 at that focus distance is the just-focus position. As described above, the just-in-focus position can be determined by using the optical path difference prism 33 and the like.

[0046] Another method for determining the just-focus position will be described below: The just-focus position may be determined using the processing unit 13 (see FIG. 1) that performs image processing. The processing unit 13 performs image processing on the image acquired by the image capture device 25 to determine the brightness value at the center P1 of the field of view (see FIG. 2). The brightness value is determined for each changed position while changing the focus position of the optical microscope 11. The image of the center P1 of the field of view is an image formed by multiple pixels of the image sensor 252. The focus control unit 14 acquires the brightness value of each of the multiple pixels corresponding to the center P1 of the field of view and calculates the variance of the brightness values at the center P1 of the field of view. This processing is performed at each focus position while changing the focus position, and the position where the variance value is highest is determined to be the just-focus position.

[0047] In this way, the focus control unit 14 can determine the just-focus position based on the variance value of the brightness values in the central portion P1 of the field of view of the optical microscope 11 obtained by the image processing of the processing unit 13. Then, the focus position adjustment unit 24 sets a position offset from the just focus position as the inspection focus position. The inspection unit 12 performs inspection based on the image acquired at the inspection focus position.

[0048] As described above (see FIGS. 3 and 4), the inspection device 10 of this embodiment increases the MTF value not only in the central portion P1 of the visual field but also in the peripheral portion P2 of the visual field. As a result, the average value of the MTF value across the entire visual field increases. This makes it possible to improve inspection accuracy across the entire visual field, including the peripheral portion P2 of the visual field, not just the central portion P1.

[0049] [Testing method] A method for inspecting the wafer W performed by the inspection apparatus 10 having the above configuration will now be described. The inspection is an appearance inspection of the pattern provided on the wafer W. For example, an inspection is performed to check for defects such as foreign matter contained in the pattern, chipping of the pattern, or peeling of the pattern. 1 is used for the inspection, the processing unit 13 processes the acquired image, and the inspection unit 12 makes a pass / fail judgment based on the brightness value of the image data, for example. The pass / fail judgment is made by comparing the brightness value based on the acquired image with a preset brightness threshold value, for example.

[0050] [Testing method (1)] As described above, the focus control unit 14 can determine the just-in-focus position for the wafer W. The optical microscope 11 has a movement mechanism 23, which performs relative movement in the X-axis and Y-axis directions between the objective lens 21 and the stage 22 on which the wafer W is placed. The inspection method (1) is a method using scan imaging in which the stage 22 is moved while imaging.

[0051] 6 is a flow diagram showing an inspection method. The inspection apparatus 10 reads pre-registered inspection recipe data (step ST110). The inspection recipe data is data related to the inspection of the wafer W to be inspected, and includes, for example, data on the threshold value for pass / fail judgment.

[0052] Moreover, the inspection recipe data is data on the objective lens 21 used for the inspection, and includes correspondence information K for the objective lens 21. Correspondence information K for each of the plurality of objective lenses 21 is stored in the storage unit 15 (step ST100). Then, correspondence information K according to the objective lens 21 to be used is extracted from the storage unit 15 (step ST110), and the correspondence information K is used. As described above, the correspondence information K is information indicating the relationship between the objective lens 21 and data related to the offset amount.

[0053] The wafer W to be inspected is placed on the stage 22 (step ST120). The scan imaging is performed (step ST130). That is, while the moving mechanism 23 performs the relative movement, the focus position adjusting unit 24 sets a position offset from the acquired just focus position as the inspection focus position, and the imaging device 25 performs imaging every moment at that inspection focus position (step ST130). The processing unit 13 performs image processing on the images acquired at each position of the relative movement, and the inspection unit 12 performs inspection processing (step ST140). That is, photographing is performed every moment along with the relative movement (ST130), and inspection processing is performed on the entire wafer W. The inspection processing (ST140) may be performed during the relative movement, or may be performed after (delayed from) the relative movement.

[0054] In the case of scan imaging, the mechanism shown in FIG. 5 is used to determine the just-in-focus position. In the case of scan imaging, the focus control unit 14 acquires the just focus position, and sets a position offset from the just focus position as the inspection focus position. The amount of offset is based on the correspondence information K extracted in step ST110.

[0055] The focus position adjusting unit 24 performs the relative movement by the moving mechanism 23 so as to keep constant the focus distance corresponding to the set inspection focus position. While performing the relative movement, a position offset from the just focus position is set as the inspection focus position. Therefore, even if the wafer W has an uneven wave shape, it is possible to increase the MTF value in the peripheral part P2 of the field of view as described above (see FIGS. 3 and 4). As a result, it is possible to improve the inspection accuracy not only in the central part P1 of the field of view but also in the entire field of view including the peripheral part P2.

[0056] After the inspection, the wafer W is removed from the stage 22 (step ST150). A plurality of wafers W are accommodated in a cassette (not shown). Each step from step ST120 to step ST150 is repeatedly performed until all wafers W have been inspected (step ST160). In the case of the inspection method (1), the image is acquired while the stage 22 and the objective lens 21 are moving relative to each other, which makes it possible to shorten the time required for the inspection.

[0057] [Testing method (2)] In steps ST130 and ST140 of FIG. 6, another inspection method may be performed. In the case of the above-mentioned inspection method (1), the inspection focus position is set at each movement position while the moving mechanism 23 performs the relative movement, and an image is acquired. In contrast, in the case of another inspection method (2), imaging is performed using a stop-and-go method.

[0058] That is, while the moving mechanism 23 temporarily stops the relative movement, the focus control unit 14 acquires the just focus position, and the focus position adjustment unit 24 sets a position offset from the just focus position as the inspection focus position. The amount of offset is based on the correspondence information K that has been extracted in step ST110. At the inspection focus position, an image is acquired by the imaging device 25 (step ST130), and inspection is performed based on the image (step ST140).

[0059] In the case of stop-and-go imaging, the mechanism shown in FIG. 5 may be used to determine the just-in-focus position, or another means based on the variance of brightness values as described above may be used.

[0060] [Regarding inspection methods (1) and (2)] As described above, each of the inspection methods (1) and (2) includes a focus position adjusting step and an image acquiring step in step ST130. The focus position adjustment process is a process of adjusting the inspection focus position for inspection by the optical microscope 11. The focus position adjustment process includes a preliminary process of determining the just focus position for the wafer W. In the focus position adjustment process, a position offset from the just focus position for the wafer W by a previously acquired offset amount is set as the inspection focus position.

[0061] The image acquisition process is a process of acquiring an image of a pattern on the wafer W at a set inspection focus position. Then, in each of the inspection methods (1) and (2), an inspection is performed based on the image acquired at the inspection focus position in the inspection process (process ST140).

[0062] Whether it is the case of inspection method (1) or inspection method (2), the storage unit 15 stores correspondence information K indicating the relationship between the objective lens 21 and data related to the offset amount. The focus control unit 14 acquires the offset amount for the objective lens 21 to be used from data (the inspection recipe data) of that objective lens 21 and the correspondence information K. Then, the focus position adjustment unit 24 sets a position offset by the offset amount from the just focus position as the inspection focus position. Since the correspondence information K is acquired in advance, setting of the offset amount becomes easy, and inspection efficiency improves.

[0063] [How to obtain the offset amount] As described above, the offset amount is determined in advance before the inspection. A method for acquiring the offset amount will be described below. The method for acquiring the offset amount uses the inspection device 10 shown in Figures 1 and 5. Figure 7 is a flow chart showing the method for acquiring the offset amount.

[0064] A substrate is placed on the stage 22 of the optical microscope 11. An image of the substrate is acquired by the imaging device 25 (step ST10). The substrate may be a wafer W to be a product, or may be a test wafer W having the same specifications as the product. Processing unit 13 acquires image parameters for the central portion P1 of the visual field (see FIG. 2) from the acquired image through image processing (step ST20). In this embodiment, the image parameters are MTF values, but may be other image parameters such as luminance values.

[0065] Steps ST10 and ST20 are performed multiple times while gradually changing the focus position (step ST30). At each changed focus position, the MTF value in the central part P1 of the field of view is obtained. The focus position where the MTF value in the central part P1 of the field of view is the highest is selected. The selected focus position is determined as the just-focus position (step ST40). This selection may be performed by the processing unit 13 or by other means.

[0066] The focus position is offset (changed little by little) from the selected just focus position in the vertical direction (Z-axis direction), and an image is acquired by the imaging device 25 (step ST50) in the same manner as in step ST10. Processing unit 13 performs image processing to acquire MTF values for the central portion P1 of the visual field and for the peripheral portion P2 of the visual field from the image acquired in step ST50 (step ST60). The MTF values for the peripheral portion P2 of the visual field need only be acquired for at least one position, but are preferably acquired for multiple positions. For example, MTF values are acquired for multiple locations, such as the four corner positions of the peripheral portion P2 of the visual field (see FIG. 2) and positions closer to the central portion P1 of the visual field than each of the four corners.

[0067] Statistical values are calculated for the MTF values in the central portion P1 of the field of view and the MTF values in the peripheral portion P2 of the field of view for each of the different focus positions acquired in step ST60. In this embodiment, the average value is used as the statistical value, but the statistical value may be other statistical values such as the standard deviation. The offset amount is calculated from the focus position where the average value is highest and the just focus position determined in step ST40 (step ST70). That is, the offset amount is the difference between the focus position where the average value is highest and the just focus position determined in step ST40.

[0068] The offset amount is a positive value when the focus position where the average value is highest is on one side (upper side) of the Z axis direction, and a negative value when the focus position where the average value is highest is on the other side (lower side) of the Z axis direction. The process of obtaining the statistical values and the calculation of the offset amount may be performed by the processing unit 13 or by other means. In this way, the offset amount is determined based on the focus position at which the average value of the MTF value over the entire visual field, including the central part P1 and the peripheral part P2 of the visual field, is highest.

[0069] The above-described steps from step ST10 to step ST70 are performed for each of the objective lenses 21 included in the optical microscope 11. As a result, the offset amount (data related to the offset amount) determined for each objective lens 21 can be stored in the storage unit 15 as correspondence information K (step ST100). Even if the characteristics of each objective lens 21 differ, the offset amount is set for each objective lens 21. This correspondence information K is used in the inspection method (see FIG. 6).

[0070] As described above, the offset amount acquisition method of this embodiment includes, in step ST50, an imaging step ST51 in which the optical microscope 11 acquires an image of the wafer W through the objective lens 21, a parameter acquisition step ST52 in which the MTF value in the image acquired by the optical microscope 11 is acquired, and an offset amount acquisition step ST70 in which the offset amount corresponding to the objective lens 21 is acquired based on the MTF value.

[0071] In the photographing step ST51, an image of the wafer W is acquired while changing the focus position of the optical microscope 11. In the parameter acquisition step ST52, the MTF value of the image acquired by the optical microscope 11 at each of the changed focus positions is acquired.

[0072] In the offset amount acquisition process ST70, the offset amount is acquired based on the average value of the MTF value in the central part of the image (central part P1 of the field of view) and the MTF value in the peripheral part of the image (peripheral part P2 of the field of view) at each changed focus position. The acquired offset amount is associated with the objective lens 21 used in this acquisition method and stored as association information K in the storage unit 15 (ST100).

[0073] 〔others〕 The embodiments disclosed herein are illustrative in all respects and are not restrictive. The technical scope of the present invention is not limited to the above-described embodiments, and includes all modifications within the scope of equivalents to the configurations described in the claims. [Explanation of symbols]

[0074] 10 Inspection equipment 11 Optical microscope 12 Inspection Department 13 Processing section 14 Focus control section 15 Storage section 21 Objective Lens 22 Stages 23 Moving mechanism 24 Focus position adjustment section K Compatibility Information W wafer (substrate) ST51 shooting process ST52 Parameter acquisition process ST70 offset amount acquisition process

Claims

1. An inspection apparatus for inspecting a pattern provided on a substrate, comprising: an optical microscope for acquiring an image of the pattern; an inspection unit that performs an inspection based on the image; and The optical microscope a focus position adjusting unit that sets a position offset from a just focus position for the substrate as an inspection focus position for inspection; the inspection unit performs inspection based on the image acquired at the inspection focus position. Inspection equipment.

2. a focus control unit for determining a just-focus position for the substrate; the optical microscope includes an objective lens, a stage on which the substrate is placed, and a movement mechanism that moves the objective lens and the stage relative to each other; while the moving mechanism performs the relative movement, the focus position adjusting unit sets a position offset from the just focus position as the inspection focus position. The inspection device according to claim 1 .

3. a focus control unit for determining a just-focus position for the substrate; the optical microscope includes an objective lens, a stage on which the substrate is placed, and a movement mechanism that moves the objective lens and the stage relative to each other; while the moving mechanism temporarily stops the relative movement, the focus control unit acquires the just focus position, and the focus position adjustment unit sets a position offset from the just focus position as the inspection focus position. The inspection device according to claim 1 .

4. a storage unit that stores correspondence information indicating a relationship between the objective lens and data relating to the offset amount; a focus control unit that acquires data regarding the offset amount from the objective lens to be used and the correspondence information; and The focus position adjustment unit a position offset from the just focus position by the offset amount is set as the inspection focus position; The inspection device according to any one of claims 1 to 3.

5. the optical microscope has a plurality of objective lenses; the storage unit stores the correspondence information for each of the plurality of objective lenses. The inspection device according to claim 4.

6. An inspection method for inspecting a pattern provided on a substrate, comprising: a focus position adjusting step of adjusting an inspection focus position for inspection by an optical microscope; an image acquisition step of acquiring an image of the pattern at the inspection focus position; an inspection step of performing an inspection based on the image; and In the focus position adjusting step, a position offset from a just focus position for the substrate is set as the inspection focus position; In the inspection step, performing an inspection based on the image acquired at the inspection focus position; Testing method.

7. 1. A method for acquiring an offset amount to be offset from a just focus position of an optical microscope in order to set an inspection focus position of the optical microscope with respect to a substrate, the method comprising: an imaging step in which the optical microscope acquires an image of the substrate through an objective lens; a parameter acquisition step of acquiring image parameters of the image acquired by the optical microscope; an offset amount acquisition step of acquiring the offset amount corresponding to the objective lens based on the image parameters; and In the photographing step, acquiring an image of the substrate while changing the focus position of the optical microscope; In the parameter acquisition step, acquiring the image parameters for the images acquired by the optical microscope at each of the changed focus positions; In the offset amount acquisition step, acquiring the offset amount based on statistics of the image parameters of the central part of the image and the image parameters of the peripheral part of the image at each of the changed focus positions; How to obtain the offset amount.

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