Imaging device and focus adjustment method

Abstract

To provide an imaging device and a focus adjustment method that can suppress defocus.SOLUTION: An imaging device 1 according to the present disclosure comprises: a measurement point acquisition unit 41 that acquires each measurement point 54 set at a plurality of positions when a measurement surface 53 of a sample 50 is viewed from above; a height information detection unit 30 that detects height information indicative of a height of the measurement surface 53; a drive control unit 43 that controls a position of the height information detection unit 30 with respect to the sample 50 so that the height information detection unit 30 scans a measurement area 59 including the vicinity of the measurement point 54, and detects a plurality of pieces of height information in the measurement area 59; a height data acquisition unit 42 that defines the most frequent value as height information on the measurement point 54, of the plurality of pieces of detected height information in the measurement area 59, and acquires each height data on a plurality of measurement points 54; and an imaging unit 20 that images the measurement surface 53, in which the drive control unit 43 adjusts focus of the imaging unit 20 on the basis of each acquired height data on the plurality of measurement points 54.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an imaging device and a focus adjustment method. [Background technology]

[0002] For example, in defect inspection of photomasks using EUV (Extreme Ultraviolet) light, the depth of focus is shallower than the amount of deflection caused by the photomask's own weight, so it is necessary to measure and calculate the deflection of the photomask and correct the focal position when imaging the photomask.

[0003] The imaging device of Patent Document 1 measures the height of the outer periphery of the photomask, which has no pattern, and predicts the curved surface of the central part of the photomask, which has a pattern, because the pattern on the photomask causes outliers in the autofocus (AF). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-018307 [Patent Document 2] Japanese Patent Application Publication No. 04-065619 [Patent Document 3] Japanese Patent Application Publication No. 05-087544 [Patent Document 4] Special Publication No. 2017-510791 Summary of the Invention [Problem to be solved by the invention]

[0005] Even if the height of the central part of the photomask is predicted from the height information of the outer periphery of the photomask and the focal position is corrected to the predicted height of the central part of the photomask, there are cases where the error is large, resulting in defocusing.

[0006] The present disclosure has been made to solve such problems, and an object of the present disclosure is to provide an imaging apparatus and a focus adjustment method that can suppress defocusing. [Means for solving the problem]

[0007] The imaging device according to the present disclosure comprises a measurement point acquisition unit that acquires each of the measurement points set at multiple positions when the measurement surface of the sample is viewed from above; a height information detection unit that detects height information indicating the height of the measurement surface; a drive control unit that controls the position of the height information detection unit relative to the sample so that the height information detection unit scans a measurement area including the vicinity of the measurement point and detects multiple pieces of height information in the measurement area; a height data acquisition unit that acquires height data for each of the multiple measurement points by using the most frequent value of the multiple pieces of height information detected in the measurement area as height information for the measurement point and acquiring height data including the position and height information of the measurement point; and an imaging unit that images the measurement surface, and the drive control unit adjusts the focus of the imaging unit based on the acquired height data for each of the multiple measurement points.

[0008] In the imaging device, the measurement point acquisition unit may use a mask having a central region and a peripheral region as the sample, acquire the plurality of measurement points set in the central region where a pattern is formed, and the drive control unit may control the height information detection unit to scan in the measurement region including the edge of the pattern in the central region in a direction intersecting the direction in which the edge of the pattern extends.

[0009] In the imaging device, the measurement point acquisition unit acquires the multiple measurement points set in the surrounding area, the drive control unit controls the position of the height information detection unit so that the height information detection unit detects the height information at the measurement points in the surrounding area, and the height data acquisition unit acquires height data including the positions of the measurement points in the surrounding area and the height information detected at the measurement points in the surrounding area, thereby acquiring height data for each of the multiple measurement points in the surrounding area.

[0010] The imaging device may further include a stage that supports the sample at a plurality of support points; a deflection data acquisition unit that acquires deflection data corresponding to deflection of the sample supported on the stage; a difference value calculation unit that calculates a difference value between a height indicated by the height data and a height indicated by the deflection data at the plurality of measurement points; a correction data calculation unit that calculates correction data based on the difference value; and an estimation unit that calculates estimation data for estimating the height of the sample by correcting the deflection data using the correction data, and the drive control unit may adjust the focus based on the estimation data in order to image the sample.

[0011] In the imaging device, the correction data calculation section may calculate the correction data using a biharmonic equation.

[0012] The imaging device may further include an illumination light source that generates illumination light, an optical element that collects light from the sample illuminated by the illumination light, and a detector that detects the light from the optical element, and the drive control unit may perform autofocus by changing the distance between the optical element and the sample based on the height of the estimated data.

[0013] In the imaging device, the deflection data may be obtained by numerical analysis.

[0014] The focus adjustment method according to the present disclosure comprises the steps of acquiring measurement points set at multiple positions when the measurement surface of a sample is viewed from above; controlling the position of the height information detection unit relative to the sample so that a height information detection unit that detects height information indicating the height of the measurement surface scans a measurement area including the vicinity of the measurement point and detects multiple pieces of height information in the measurement area; acquiring height data for each of the multiple measurement points by using the most frequent value of the multiple pieces of height information detected in the measurement area as height information for the measurement point and acquiring height data including the position and height information of the measurement point; and adjusting the focus of an imaging unit that images the measurement surface based on the acquired height data for each of the multiple measurement points.

[0015] In the above-described focus adjustment method, in the step of acquiring each set measurement point, a mask having a central region and a peripheral region is used as the sample, and the plurality of measurement points set in the central region where a pattern is formed are acquired. In the step of controlling the position of the height information detection unit relative to the sample, the height information detection unit may be controlled to scan in the measurement region including the edge of the pattern in the central region in a direction intersecting the direction in which the edge of the pattern extends.

[0016] In the above-described focus adjustment method, in the step of acquiring each set measurement point, the multiple measurement points set in the peripheral region are acquired; in the step of controlling the position of the height information detection unit relative to the sample, the height information detection unit is controlled to detect the height information at the measurement points in the peripheral region; and in the step of acquiring each height data of the multiple measurement points, height data including the positions of the measurement points in the peripheral region and the height information detected at the measurement points in the peripheral region is acquired, thereby acquiring each height data of the multiple measurement points in the peripheral region.

[0017] The focus adjustment method further includes the steps of: acquiring deflection data corresponding to deflection of the sample supported on a stage having a plurality of support points; calculating a difference value between the height indicated by the height data and the height indicated by the deflection data at the plurality of measurement points; calculating correction data based on the difference value; and calculating estimated data for estimating the height of the sample by correcting the deflection data using the correction data; and in the step of adjusting the focus of an imaging unit that images the measurement surface, the focus may be adjusted using the estimated data.

[0018] In the focus adjustment method, in the step of calculating the correction data, the correction data may be calculated using a biharmonic equation.

[0019] In the above focus adjustment method, in the step of controlling the position of the height information detection unit relative to the sample, a detector may detect light from the sample illuminated with illumination light via an optical element, and in the step of adjusting the focus of an imaging unit that images the measurement surface, autofocus may be performed by changing the distance between the optical element and the sample based on the height of the estimated data.

[0020] In the focus adjustment method, in the step of acquiring the deflection data, the deflection data may be acquired by numerical analysis. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an imaging apparatus and a focus adjustment method that can suppress defocusing. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a configuration diagram illustrating a schematic example of an imaging device according to a first embodiment. [Figure 2] 2 is a block diagram illustrating a processing device in the imaging device according to the first embodiment. FIG. [Figure 3] 3 is a top view illustrating an example of the arrangement of support pins in the imaging device according to the first embodiment. FIG. [Figure 4] 3 is a side view illustrating the configuration of a height information detection unit according to the first embodiment. FIG. [Figure 5] 3 is a plan view illustrating measurement points acquired by a measurement point acquisition unit in the imaging device according to the first embodiment. FIG. [Figure 6] 3 is a plan view illustrating measurement points acquired by a measurement point acquisition unit in the imaging device according to the first embodiment. FIG. [Figure 7] FIG. 10 is a plan view illustrating height information in a case where measurements are made one point at a time in an imaging device according to a comparative example, and the height information is shown in gray scale. [Figure 8] 1 is a graph illustrating height information detected in each measurement area by a height information detection unit in an imaging device according to embodiment 1, where the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates height information. [Figure 9] 9 is a graph illustrating the height information shown in IX of FIG. 8 detected by the height information detection unit in the imaging device according to the first embodiment, where the horizontal axis represents the height information and the vertical axis represents the frequency. [Figure 10] Figure 10A is a plan view illustrating height information detected by single-point measurement in an imaging device related to a comparative example, where the height information is shown in grayscale, and Figure 10B is a plan view illustrating height information detected by a height information detection unit in an imaging device related to embodiment 1 by scanning diagonally with respect to the direction in which the edge of the pattern extends, where the height information is shown in grayscale. [Figure 11] FIG. 3 is a flowchart illustrating a focus adjustment method according to the first embodiment. [Figure 12] 10 is a block diagram illustrating a processing device in an imaging device according to a second embodiment. FIG. [Figure 13] 10 is a three-dimensional graph illustrating deflection data in the imaging device according to the second embodiment, where the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates the amount of deflection. [Figure 14]10 is a three-dimensional graph illustrating height information of measurement points in the peripheral area of ​​a sample detected by a height information detection unit in an imaging device according to embodiment 2, in which the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates height information. [Figure 15] 10 is a three-dimensional graph illustrating the correction data calculated by the correction data calculation unit in the imaging device according to the second embodiment, where the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates the amount of deformation. [Figure 16] 10 is a three-dimensional graph illustrating estimated data estimated by an estimation unit in an imaging device according to embodiment 2, where two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates the amount of deformation. [Figure 17] FIG. 10 is a flowchart illustrating a focus adjustment method according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a specific configuration of this embodiment will be described with reference to the drawings. The following description shows a preferred embodiment of the present disclosure, and the scope of the present disclosure is not limited to the following embodiment. In the following description, components with the same reference numerals indicate substantially the same content.

[0024] (Embodiment 1) The imaging device of this embodiment, for example, captures an image of a sample. The imaging device may be used in an inspection device. That is, the inspection device may inspect the sample based on an image (hereinafter referred to as a sample image) captured by the imaging device. The sample is, for example, a photomask on which a fine pattern is formed. Note that the sample is not limited to a photomask, and may be a semiconductor wafer or the like on which a fine pattern is formed. The inspection device performs inspection using information about the sample image. For example, the inspection device detects defects by setting a predetermined signal intensity of the sample image as a threshold or by comparing the sample image with other images. In the following explanation, a photomask used in the photolithography process of a semiconductor device will be described as the sample.

[0025] An imaging device and a focus adjustment method according to this embodiment will be described with reference to the drawings. FIG. 1 is a configuration diagram that schematically illustrates an imaging device according to embodiment 1. FIG. 2 is a block diagram that illustrates a processing device in the imaging device according to embodiment 1. As shown in FIGS. 1 and 2, the imaging device 1 includes a stage 10, an imaging unit 20, a height information detection unit 30, and a processing device 40. The processing device 40 includes a measurement point acquisition unit 41, a height data acquisition unit 42, and a drive control unit 43. The imaging device 1 images a sample 50.

[0026] Here, for ease of explanation of the imaging device 1, an XYZ Cartesian coordinate system is introduced. For example, the vertical direction is the Z-axis direction, the upward direction is the +Z-axis direction, and the downward direction is the −Z-axis direction. The Z-axis direction is parallel to the thickness direction of the sample 50. Therefore, the Z-axis direction is the height direction. A pattern 51 such as a light-shielding film is formed on the upper surface of the sample 50. The Z-axis direction is the normal direction to the main surface, such as the pattern-formed surface, of the sample 50. The X-axis and Y-axis directions are horizontal directions and parallel to the pattern direction of the sample 50. If the sample 50 is a photomask, the sample 50 may be rectangular when viewed from above. The X-axis and Y-axis directions may be parallel to the edge of the sample 50. Note that the relationship between the XYZ Cartesian coordinate system and the vertical and horizontal directions is introduced for ease of explanation of the imaging device 1 and does not limit the actual arrangement direction of the imaging device 1.

[0027] A sample 50 to be inspected is placed on the stage 10. The stage 10 is a three-dimensional drive stage, and is driven in the X-axis, Y-axis, and Z-axis directions under the control of a drive control unit 43 of the processing device 40. Note that the control of the stage 10 by the drive control unit 43 is not limited to control in the X-axis, Y-axis, and Z-axis directions, and may also include attitude control such as rotation direction.

[0028] The stage 10 may include a pedestal 11 and support pins 12. A plurality of support pins 12 are provided on the upper surface of the pedestal 11. That is, the support pins 12 protrude from the pedestal 11 in the +Z-axis direction. The sample 50 is placed on the support pins 12. The upper surfaces of the support pins 12 abut against the lower surface of the sample 50. The support pins 12 serve as support points for the sample 50. In this way, the stage 10 supports the sample 50 at a plurality of support points. The heights of the plurality of support pins 12 may be the same.

[0029] FIG. 3 is a top view illustrating an example of the arrangement of support pins 12 in the imaging device 1 according to the first embodiment. As shown in FIG. 3, for example, a sample 50 may be supported by three support pins 12. The top surface of the sample 50 is referred to as a measurement surface 53. The measurement surface 53 of the sample 50 may have a central region 56 and a peripheral region 57. If the sample 50 is a photomask, the measurement surface 53 includes the mask surface of the photomask. In this case, the mask surface has the central region 56 and the peripheral region 57. The mask surface may also include a pattern-formed surface. A pattern is formed in the central region 56 of the mask surface. No pattern is formed in the peripheral region 57 of the mask surface.

[0030] For example, three support pins 12 may support the peripheral region 57 of the sample 50 from below. The number of support pins 12 is not limited to three and may be four or more. When the sample 50 is supported by three support pins, for example, the sample 50 is supported by the support pins 12 at the upper right corner, the lower right corner, and the center of the left edge of the rectangular sample 50. The arrangement of the support pins 12 is not limited to the arrangement shown in FIG. 3. Furthermore, the support points are not limited to three points. The sample 50 may be supported by a support member other than the support pins 12.

[0031] As shown in FIG. 1, the imaging unit 20 constitutes an imaging optical system. The imaging unit 20 captures an image of a measurement surface 53 of a sample 50. The measurement surface 53 of the sample 50 is, for example, a mask surface. The imaging unit 20 includes, for example, a light source 21, a beam splitter 22, an objective lens 23, and an imaging element 24. Note that the imaging unit 20 shown in FIG. 1 is appropriately simplified. In addition to the above configuration, the imaging unit 20 may include optical elements such as lenses, optical scanners, mirrors, filters, and beam splitters. Furthermore, the imaging unit 20 may not include some components such as the beam splitter 22. For example, the imaging unit 20 may be a confocal optical system.

[0032] The light source 21 generates illumination light L11. The light source 21 may be a lamp light source, an LED (Light Emitting Diode) light source, a laser light source, or the like. The illumination light L11 from the light source 21 is incident on a beam splitter 22. The beam splitter 22 is, for example, a half mirror, and reflects approximately half of the illumination light L11 toward the sample 50. The illumination light L11 reflected by the beam splitter 22 is incident on an objective lens 23. The objective lens 23 focuses the illumination light L11 on the sample 50. This makes it possible to illuminate a measurement surface 53, such as a pattern-formed surface of the sample 50. The optical axis OX of the objective lens 23 is parallel to the Z-axis direction. Alternatively, the illumination light L11 may be focused using another optical element, such as an objective reflecting mirror, instead of the objective lens 23.

[0033] The reflected light L12 reflected by the measurement surface 53 of the sample 50 is collected by the objective lens 23 and enters the beam splitter 22. The beam splitter 22 transmits approximately half of the reflected light L12. The reflected light L12 that has passed through the beam splitter 22 enters the image sensor 24. Thus, an image of the sample 50 can be captured. A lens or the like may be provided to form an image of the reflected light L12 on the light-receiving surface of the image sensor 24.

[0034] The image sensor 24 is a two-dimensional array sensor such as a CCD (Charge Coupled Device) camera or a CMOS (Complementary Metal Oxide Semiconductor) sensor. Alternatively, the image sensor 24 may be a photodetector such as a line sensor, a photodiode, or a photomultiplier tube. As described above, the imaging unit 20 includes an optical element that collects light from the sample 50 illuminated with illumination light, and a detector that detects the light from the optical element. The image sensor 24 outputs detection data corresponding to the amount of received light to the processing device 40. The processing device 40 inspects the sample 50 based on the reflection luminance value indicated by the detection data. Since a known method can be used for the inspection process, a description thereof will be omitted.

[0035] The stage 10 is a movable stage, and can move the sample 50 in the X-axis and Y-axis directions. A drive control unit 43 of the processing device 40 controls the driving of the stage 10. The drive control unit 43 moves the stage 10 in the X-axis and Y-axis directions, thereby changing the illumination position on the sample 50. This makes it possible to image any position on the sample 50, and to inspect the entire measurement surface 53 of the sample 50. Of course, the drive control unit 43 may drive the imaging unit 20 instead of the stage 10. In other words, it is sufficient that the relative position of the imaging unit 20 with respect to the stage 10 is movable. Alternatively, the illumination light L11 may be scanned using an optical scanner or the like.

[0036] Furthermore, the stage 10 can move the sample 50 in the Z-axis direction. This allows the focus position to be aligned with the measurement surface 53 of the sample 50. In other words, when the drive control unit 43 moves the stage 10 in the Z-axis direction, the distance between the objective lens 23 and the sample 50 in the Z-axis direction changes. This allows focus adjustment. The imaging unit 20 can image the sample 50 while the measurement surface 53 of the sample 50 is in focus. This allows the sample 50 to be properly inspected. Of course, the focus may be adjusted by moving the imaging unit 20 in the Z-axis direction instead of the stage 10. The drive control unit 43 drives the stage 10 or the objective lens 23 to perform focus adjustment.

[0037] Next, the height information detecting unit 30 will be described. The height information detecting unit 30 detects height information indicating the height of the measurement surface 53 of the sample 50. FIG. 4 is a side view illustrating the configuration of the height information detecting unit 30 according to the first embodiment. Here, the height information detecting unit 30 detects the height information of the measurement surface 53 of the sample 50 by an optical lever method. By using the optical lever method, height information can be detected even when there is no specific pattern for detection.

[0038] The height information detecting unit 30 detects the position of the measurement surface 53 of the sample 50 in the Z-axis direction as height information. The measurement surface 53 of the sample 50 is, for example, a mask surface. The mask surface includes a pattern-formed surface 52 on which a pattern is formed. Note that the measurement surface 53 is not limited to the mask surface, but may also be the upper surface of a mask without a pattern 51, the upper surface of a semiconductor substrate, or the like. In the following, the measurement surface 53 will be described as the pattern-formed surface 52. The sample 50 deforms due to bending caused by its own weight, film stress, and the like. In other words, the pattern-formed surface 52 of the sample 50 may not be a perfect plane. For this reason, the height indicated by the height information changes according to the XY coordinates. The height (Z position) of the pattern-formed surface 52 changes according to the XY coordinates. The height information detecting unit 30 detects height information associated with the XY coordinates. The height information detecting unit 30 outputs the height information to the processing device 40.

[0039] The imaging device 1 performs autofocus (AF) based on the height information detected by the height information detection unit 30. Specifically, the drive control unit 43 adjusts the Z position of the stage 10 based on the height information. Then, with the pattern formation surface 52 in focus, the imaging unit 20 images the sample 50.

[0040] The height information detection unit 30 includes an AF light source 31, lenses 32 and 33, and a photodetector 34. In FIG. 4, a case where the pattern-formed surface 52 of the sample 50 is at the reference height is shown by a solid line. On the other hand, a case where the pattern-formed surface 52 of the sample 50 is deviated from the reference height is shown by a dashed line as the pattern-formed surface 52a of the sample 50a. The reference height is, for example, the height at which the pattern-formed surface 52 of the sample 50 is located at the in-focus position of the imaging unit 20. For simplification, the pattern 51 is omitted from FIG. 4.

[0041] The AF light source 31 generates a light beam L21 for AF. The AF light source 31 is a point light source such as an LED light source or a laser diode. The light beam L21 emitted from the AF light source 31 is incident on a lens 32. The lens 32 focuses the light beam L21 on the sample 50. Here, the optical axis of the AF light source 31 is disposed at an angle with respect to the Z axis. In other words, the light beam L21 is incident on the sample 50 from an obliquely upward direction.

[0042] The light beam L22 reflected by the sample 50 is incident on the lens 33. The lenses 33 and 32 are arranged symmetrically with respect to the optical axis OX of the imaging unit 20. The lens 33 focuses the light beam L22 on the light receiving surface of the photodetector 34. The light beam L21 is incident on the sample 50 from an oblique direction. The optical axes of the light beams L21 and L22 are tilted from the Z axis. When the height of the sample 50 changes, the light receiving position on the photodetector 34 changes. For example, when the pattern-formed surface 52 of the sample 50 is at a reference height, the light beam L22 is incident on the center of the photodetector 34. When the pattern-formed surface 52a of the sample 50a is shifted from the reference height, the incident position of the light beam L23 shifts from the center position of the photodetector 34.

[0043] The photodetector 34 is, for example, a two-part photodiode, and includes two photodiodes 34 a and 34 b. By comparing the amounts of light received by the photodiodes 34 a and 34 b of the photodetector 34, the amount of deviation of the sample 50 from the reference height can be determined.

[0044] For example, when the pattern formation surface 52 is at the reference height, half of the light beam L22 is received by the photodiode 34a and the other half is received by the photodiode 34b. The amounts of light received by the photodiode 34a and the photodiode 34b are the same.

[0045] When the pattern-forming surface 52a is higher than the reference height, the amount of light received by the photodiode 34a is lower than that of the photodiode 34b. When the pattern-forming surface 52a is lower than the reference height, the amount of light received by the photodiode 34a is higher than that of the photodiode 34b. Furthermore, the more the pattern-forming surface 52a deviates from the reference height, the greater the difference in the amount of light received by the two photodiodes 34a and 34b.

[0046] The height of the sample 50 can be detected by comparing the amounts of light received by the photodiodes 34a and 34b. Furthermore, autofocusing can be performed by performing feedback control so that the amounts of light received by the photodiodes 34a and 34b are equal. The drive control unit 43 drives the stage 10 based on the detection result of the photodetector 34. Specifically, the drive control unit 43 changes the distance between the objective lens 23 and the sample 50 so that the difference between the output values ​​of the photodiodes 34a and 34b tracks to zero. This allows the height of the pattern-formed surface 52 to be adjusted to track the in-focus position. Therefore, the imaging unit 20 can image the sample 50 in a focused state.

[0047] The height information detecting unit 30 may detect the amount of deviation of the pattern-forming surface 52a from the reference height as the height information. Alternatively, the height information detecting unit 30 may detect the absolute Z position of the pattern-forming surface 52a as the height information. In other words, the height indicated by the height information may be an absolute position or a relative position. A part or all of the processing for calculating the height information may be performed by the processing device 40.

[0048] In the above description, a two-segment photodiode is used as the photodetector 34, but a four-segment photodiode, a position sensitive device (PSD), a CCD sensor, etc. may also be used. Even when these sensors are used, height information can be detected based on the receiving position of the light beam L22.

[0049] In FIG. 4, the height information detecting unit 30 has lenses 32 and 33, but the objective lens 23 of the imaging unit 20 may be used instead of the lenses 32 and 33. Specifically, the light beam L21 may be incident on one half of the objective lens 23. In this case, the light beam L22 reflected by the sample 50 passes through the opposite half of the objective lens 23. Even in this case, the height information detecting unit 30 can similarly detect height information. Alternatively, the height information detecting unit 30 may use optical elements other than the lenses 32 and 33.

[0050] The height information detection unit 30 may detect height information using a method other than the optical lever method. For example, the height information detection unit 30 may acquire height information using the contrast of a pattern image captured by the image sensor 24. Specifically, when the object is in focus, an image of the pattern is not blurred, resulting in high contrast. On the other hand, when the object is not in focus, an image of the pattern is blurred, resulting in low contrast. Therefore, the height information detection unit 30 can detect height information according to the contrast of the captured pattern image.

[0051] Next, the processing device 40 will be described. FIG. 5 is a plan view illustrating measurement points acquired by the measurement point acquisition unit 41 in the imaging device 1 according to the first embodiment. As shown in FIG. 5, the measurement point acquisition unit 41 acquires measurement points 54 set at multiple positions when the measurement surface 53 of the sample 50 is viewed from above. That is, the measurement point acquisition unit 41 acquires multiple measurement points 54. In FIG. 5, some reference numerals are omitted to avoid cluttering the drawing. The measurement points 54 in the central region 56 where the pattern 51 is formed are referred to as measurement points 54a, and the measurement points 54 in the peripheral region 57 where no pattern is formed are referred to as measurement points 54b. The measurement points 54a and 54b are collectively referred to as measurement points 54. The measurement point acquisition unit 41 may use a mask having a central region 56 and a peripheral region 57 as the sample 50 and acquire multiple measurement points 54a set in the central region 56 where the pattern 51 is formed. Alternatively, the measurement point acquisition unit 41 may acquire multiple measurement points 54b set in the peripheral region 57.

[0052] FIG. 6 is a plan view illustrating a measurement point 54a acquired by the measurement point acquisition unit 41 in the imaging device 1 according to the first embodiment. As shown in FIG. 6, the height information detection unit 30 scans a measurement area 59 including the vicinity of the measurement point 54a in the central area 56. The measurement area 59 includes a plurality of positions 58. The height information detection unit 30 then detects a plurality of pieces of height information in the measurement area 59. Specifically, the height information detection unit 30 detects each piece of height information for the plurality of positions 58 in the measurement area 59. For example, the height information detection unit 30 scans a width of ±2.5 mm in the measurement area 59 at a pitch of 0.1 mm to detect each piece of height information. Therefore, the height information detection unit 30 may detect height information for 50 positions 58 in the vicinity of the measurement point 54a.

[0053] Furthermore, the height information detecting section 30 may scan a measurement area 59 including the vicinity of the measurement point 54b in the peripheral area 57, and detect a plurality of pieces of height information in the measurement area 59.

[0054] For such measurements, the drive control unit 43 controls the position of the height information detection unit 30 relative to the sample 50 so that the height information detection unit 30 scans a measurement area 59 including the vicinity of the measurement point 54 and detects multiple pieces of height information in the measurement area 59.

[0055] The height data acquiring unit 42 sets the most frequent value among the multiple pieces of height information detected in the measurement area 59 as the height information of the measurement point 54. The height data acquiring unit 42 also acquires height data including the position of the measurement point 54 as viewed from above and the height information of the measurement point 54. Therefore, the height data associates the height information of the measurement surface 53 at the measurement point 54 with the XY coordinates. The height data acquiring unit 42 acquires the height data for each of the multiple measurement points 54. The drive control unit 43 adjusts the focus of the imaging unit 20, which images the measurement surface 53, based on the acquired height data for each of the multiple measurement points 54.

[0056] When the sample 50 has a pattern 51, defocusing may occur at the edge of the pattern 51 due to a sudden change in height information. For example, at the edge of the pattern 51, the autofocus may not be able to follow and jump, making it impossible to obtain accurate height information of the measurement surface 53. Such height information outside the measurement surface 53 is called an outlier.

[0057] In the imaging device 1 of this embodiment, the height information detection unit 30 scans a measurement area 59 including the vicinity of the measurement point 54. Then, the height information detection unit 30 detects height information for each of a plurality of positions 58 in the measurement area 59. The height data acquisition unit 42 sets the most frequent value of the plurality of pieces of height information detected in the measurement area 59 as the height information for the measurement point 54. Therefore, the imaging device 1 can exclude outliers, thereby suppressing defocusing.

[0058] 7 is a plan view illustrating height information in a single-point measurement performed by an imaging device according to a comparative example, where the height information is shown in grayscale. FIG. 7 shows height information for an X position in the X-axis direction and a Y position in the Y-axis direction. As shown in FIG. 7, when a sample 50 has a pattern 51, a sudden change in height information may be detected at the edge of the pattern 51. Furthermore, for example, when height information is detected along the edge of the pattern 51 extending in the Y-axis direction, outliers are detected consecutively, as shown in region 55.

[0059] Therefore, as shown in FIG. 6 , the height information detection unit 30 may scan in a measurement area 59 including the edge of the pattern 51 in a direction intersecting the direction in which the edge of the pattern 51 extends. For example, the height information detection unit 30 may scan in a direction at an angle of 45° with respect to the direction in which the edge of the pattern 51 extends. For such a measurement, the drive control unit 43 may control the height information detection unit 30 to scan in a measurement area 59 including the edge of the pattern 51 in the central area 56 in a direction intersecting the direction in which the edge of the pattern 51 extends. In this way, the height information detection unit 30 can prevent outliers from being detected continuously, compared to scanning in the direction in which the edge of the pattern 51 extends.

[0060] 8 is a graph illustrating height information detected by the height information detection unit 30 in each measurement region 59 in the imaging device 1 according to embodiment 1, where the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates height information. As shown in Fig. 8, when scanning is performed in a direction intersecting the direction in which the edge of the pattern 51 extends, the height information detection unit 30 detects a plurality of pieces of height information, including outliers, at a plurality of positions 58 in the measurement region 59.

[0061] 9 is a graph illustrating the height information shown in IX in FIG. 8 detected by the height information detection unit 30 in the imaging device 1 according to the first embodiment, where the horizontal axis represents the height information and the vertical axis represents the frequency. As shown in FIG. 9, multiple positions 58 in a measurement area 59 represent multiple pieces of height information. The height data acquisition unit 42 determines the most frequent value of the multiple pieces of height information detected in the measurement area 59 as the height information for the measurement point 54. This makes it possible to remove outliers.

[0062] 10A is a plan view illustrating height information detected by single-point measurement in an imaging device according to a comparative example, where the height information is shown in grayscale. FIG. 10B is a plan view illustrating height information detected by the height information detection unit 30 in the imaging device 1 according to embodiment 1, where the height information is shown in grayscale, where the height information is detected by scanning obliquely with respect to the direction in which the edge of the pattern 51 extends. As shown in the result of the comparative example in FIG. 10A, when a single point on the measurement surface 53 is measured, a region 101 containing a continuous series of outliers is present. In such a case, the imaging device is unable to obtain accurate height information on the measurement surface 53, making it difficult to focus on the measurement surface 53.

[0063] 10B, in this embodiment, the height information detection unit 30 scans in a direction intersecting the direction in which the edge of the pattern 51 extends. Therefore, the height information detection unit 30 can prevent continued detection of outliers compared to scanning in the direction in which the edge of the pattern 51 extends. Furthermore, the height data acquisition unit 42 uses the most frequent value as the height information of the measurement point 54 and excludes outliers. This allows the imaging device 1 to improve the accuracy of the height information of the measurement surface 53 and suppress defocusing.

[0064] In addition, in the peripheral region 57 of the measurement surface 53, the height information detection unit 30 may detect height information at the measurement point 54b without scanning the measurement region 59 including the vicinity of the measurement point 54b. For such measurements, the drive control unit 43 may control the position of the height information detection unit 30 so that the height information detection unit 30 detects height information at the measurement point 54b in the peripheral region 57. The height data acquisition unit 42 may acquire height data including the position of the measurement point 54b in the peripheral region 57 and the height information detected at the measurement point 54b in the peripheral region 57, thereby acquiring height data for each of the multiple measurement points 54b in the peripheral region 57. This simplifies the detection of height information in the peripheral region 57 and speeds up the operation of the imaging device 1.

[0065] Next, a focus adjustment method according to this embodiment will be described. Fig. 11 is a flowchart illustrating an example of the focus adjustment method according to embodiment 1. As shown in step S11 of Fig. 11, first, a plurality of set measurement points 54 are acquired. Specifically, the measurement point acquisition unit 41 acquires each of the measurement points 54 set at a plurality of positions when the measurement surface 53 of the sample 50 is viewed from above.

[0066] Next, as shown in step S12, a plurality of pieces of height information are detected in a measurement region 59 including the vicinity of the measurement point 54. Specifically, the drive control unit 43 controls the position of the height information detection unit 30 relative to the sample 50 so that the height information detection unit 30 scans the measurement region 59 including the vicinity of the measurement point 54 and detects a plurality of pieces of height information in the measurement region 59.

[0067] Next, as shown in step S13, the height data acquisition unit 42 sets the most frequent value among the multiple pieces of height information detected in the measurement area 59 as the height information of the measurement point 54. Then, the height data acquisition unit 42 acquires height data including the position and height information of the measurement point 54.

[0068] Next, as shown in step S14, it is determined whether there is a next measurement point 54. If the result is YES, that is, there is a next measurement point 54, the process returns to step S12, and steps S12 to S14 are repeated.

[0069] In step S14, if there is no next measurement point 54 and the height information of all the set measurement points 54 has been acquired (NO), the height data acquisition unit 42 acquires the height data of each of the multiple measurement points 54, as shown in step S15.

[0070] Next, as shown in step S16, the drive control unit 43 adjusts the focus. Specifically, the drive control unit 43 adjusts the focus of the imaging unit 20 that images the measurement surface 53, based on the acquired height data of each of the multiple measurement points 54. In this way, the imaging device 1 can adjust the focus.

[0071] In step S11, the measurement point acquisition unit 41 may use a mask having a central region 56 and a peripheral region 57 as the sample 50, and acquire a plurality of measurement points 54 set in the central region 56 where the pattern 51 is formed. Then, in step S12, the drive control unit 43 may control the height information detection unit 30 to scan in a measurement region 59 including the edge of the pattern 51 in the central region 56, in a direction intersecting the direction in which the edge of the pattern 51 extends.

[0072] Furthermore, in step S11, the measurement point acquisition unit 41 may acquire multiple measurement points 54 set in the surrounding area 57. Then, in step S12, the drive control unit 43 may control the height information detection unit 30 to detect height information at the measurement points 54b in the surrounding area 57. In that case, in step S13, the height data acquisition unit 42 may acquire height data including the positions of the measurement points 54b in the surrounding area 57 and the height information detected at the measurement points 54b in the surrounding area 57, thereby acquiring height data for each of the multiple measurement points 54b in the surrounding area 57.

[0073] Next, the effects of this embodiment will be described. The imaging device 1 of this embodiment uses the most frequent value of height information in the vicinity of the measurement point 54 as the height information of the measurement point 54. Therefore, the imaging device 1 can exclude outliers from the height information of multiple positions, and can suppress defocusing of the measurement surface 53.

[0074] Furthermore, the imaging device 1 of this embodiment scans the position of the height information detection unit 30 in a direction intersecting the direction in which the edge of the pattern 51 extends in a measurement area 59 that includes the edge of the pattern 51. As a result, the height information detection unit 30 does not scan in the direction in which the edge of the pattern 51 extends, and therefore does not continuously detect outliers. This makes it possible to suppress defocusing.

[0075] In the surrounding area 57, the height information detection unit 30 may detect height information at the measurement point 54b in the surrounding area 57. This allows the height information detection unit 30 to acquire height information in the surrounding area 57 without scanning the measurement area 59, thereby simplifying the detection of height information and speeding up the operation of the imaging device 1.

[0076] (Embodiment 2) Next, a description will be given of an imaging device according to embodiment 2. The imaging device of this embodiment estimates the height of the sample 50 based on the difference between the deflection of the sample 50 and the acquired height information.

[0077] 12 is a block diagram illustrating a processing device in the imaging device according to embodiment 2. As shown in FIG. 12, in the imaging device 2 of this embodiment, the processing device 40a further includes a measurement point acquisition unit 41, a height data acquisition unit 42, a drive control unit 43, a deflection data acquisition unit 44, a difference value calculation unit 45, a correction data calculation unit 46, and an estimation unit 47. The processing device 40a performs processing to estimate the shape of a measurement surface 53 of a sample 50.

[0078] The deflection data acquisition unit 44 acquires deflection data corresponding to the deflection of the sample 50. The deflection data is data indicating the amount of deflection of the sample 50 while it is supported by the stage 10. Specifically, since the positions, number, size, etc. of the support pins 12 on the stage 10 are known, the deflection data can be calculated by simulation. The deflection data is data that associates XY coordinates with the amount of deflection. The amount of deflection is indicated by the Z position relative to the support pin 12.

[0079] Fig. 13 is a three-dimensional graph illustrating deflection data in the imaging device 2 according to the second embodiment, with the two horizontal axes representing positions in the X-axis and Y-axis directions and the vertical axis representing the amount of deflection. Fig. 13 shows a curved surface of the height indicated by the deflection data, with the X and Y coordinates being the stage coordinates. The curved surface indicated by the deflection data is taken as the reference curved surface. The reference curved surface represents the amount of deformation of the sample 50 due to self-weight deflection. Here, the deflection data of the sample 50 supported by the support pins 12 shown in Fig. 3 is obtained by a numerical analysis method. Specifically, the deflection data acquisition unit 44 obtains the amount of deflection at each X and Y coordinate using the finite element method.

[0080] The deflection amount at the point supported by the support pin 12 is zero. The deflection data acquisition unit 44 calculates the deflection amount at regular intervals in the X-axis direction and the Y-axis direction. The deflection amount of the deflection data is a calculated value indicating the height of the measurement surface 53, such as the pattern-formed surface 52, of the sample 50 at each XY coordinate. Here, the deflection data acquisition unit 44 calculates the deflection amount of the sample 50 in a state where a pattern 51, such as a light-shielding film, is not formed, and uses this as the deflection data. For example, the deflection data acquisition unit 44 calculates the deflection data using the thickness, material, and size of the photomask substrate that serves as the sample 50, and the position, number, size, etc. of the support pins 12. Of course, the deflection data acquisition unit 44 may also calculate the deflection amount of the sample 50 in a state where a pattern 51 is formed.

[0081] Although the deflection data acquisition unit 44 calculates the deflection data by performing numerical analysis, the deflection data may be calculated by a device different from the processing device 40a. In this case, the processing device 40a stores the deflection data in advance in a memory or the like. The deflection data acquisition unit 44 reads the deflection data from the memory or the like. Alternatively, the deflection data may be saved in another device such as a server. In this case, the deflection data acquisition unit 44 downloads the deflection data via a network. Note that the deflection amount in the deflection data is not limited to a calculated value obtained by simulation, but may also be an actual measured value obtained by measuring a standard sample using a measuring instrument.

[0082] 14 is a three-dimensional graph illustrating height information of a measurement point 54 in a peripheral region 57 of a sample 50 detected by the height information detection unit 30 in the imaging device 2 according to the second embodiment, where the two horizontal axes indicate positions in the X-axis and Y-axis directions, and the vertical axis indicates height information. As shown in FIG. 14, the height information detection unit 30 detects height information of the peripheral region 57. In the peripheral region 57, the height information detection unit 30 may detect height information of the measurement point 54b by measuring a single point of the measurement point 54b, or may scan a measurement region 59 including the vicinity of the measurement point 54b and detect height information from the most frequent value of multiple pieces of height information, as in the first embodiment.

[0083] When the height information detection unit 30 detects height information by single-point measurement of the measurement point 54b in the peripheral region 57 of the sample 50, the height data acquisition unit 42 acquires the height information detected by single-point measurement of the measurement point 54b as the height information of the measurement point 54b.

[0084] The height data acquisition unit 42 may use the most frequent value among the multiple pieces of height information detected by scanning in the measurement area 59 of the central area 56 and the peripheral area 57 as the height information of the measurement point 54. The height data acquisition unit 42 may then acquire height data including the position and height information of the measurement point 54, thereby acquiring the height data of each of the multiple measurement points 54.

[0085] The differential value calculation unit 45 calculates differential values ​​between the height indicated by the height data and the height indicated by the deflection data at multiple measurement points 54. The differential values ​​are data indicating the difference between the measured value and the calculated value for the deformation amount of the sample 50. The differential value calculation unit 45 calculates differential values ​​for each measurement point 54. In FIG. 5, there are 17 measurement points 54, so the differential value calculation unit 45 calculates 17 differential values. The differential value calculation unit 45 calculates the same number of differential values ​​as the number of measurement points 54. Furthermore, differential values ​​at points supported by the support pins 12 may be added. The differential value at points supported by the support pins 12 is 0. The differential values ​​at points supported by the support pins 12 can be found without measurement. This makes it possible to obtain more differential values, thereby improving accuracy.

[0086] If the deflection amount at the XY coordinates of the measurement point 54 is not included in the deflection data, the difference value calculation unit 45 may interpolate the deflection amount in the vicinity of the measurement point 54. In other words, the difference value calculation unit 45 may find the deflection amount at the XY coordinates of the measurement point 54 by interpolating the deflection amount of the deflection data.

[0087] The correction data calculation unit 46 calculates correction data based on the difference value. The correction data is data indicating the amount of correction for each X and Y coordinate. FIG. 15 is a three-dimensional graph illustrating an example of correction data calculated by the correction data calculation unit 46 in the imaging device 2 according to the second embodiment, where the two horizontal axes indicate positions in the X and Y axis directions and the vertical axis indicates the amount of deformation. As shown in FIG. 15, the curved surface indicated by the correction data is defined as a correction curved surface. The correction curved surface is a curved surface for correcting the reference curved surface to the surface shape of the actual pattern formation surface.

[0088] The correction data indicates the amount of deformation due to components other than the self-weight deflection of the sample 50. For example, the sample 50 deforms due to membrane stress, etc. The components other than the self-weight deflection are dominated by low-frequency components. Therefore, the correction data calculation unit 46 can extract only the low-frequency components based on the difference value at the measurement point 54.

[0089] The correction data calculation unit 46 can calculate the correction data using a biharmonic equation. The calculation principle of the correction surface will be explained below. When the interpolation surface satisfies the biharmonic equation, it satisfies the minimum curvature. The biharmonic equation is expressed by the following equation (1).

[0090]

number

[0091] Biharmonic operator Δ 2 By linearly combining the Green's functions, it is possible to form a smooth curved surface that passes through the measurement point 54. The Green's function φ of the biharmonic operator is given by (2) below.

[0092]

number

[0093] δ(x) is the delta function. In the case of two-dimensional space (XY space), the Laplace operator Δ is expressed as the following equation (3).

[0094]

number

[0095] The Green's functions that satisfy the above are linearly combined to create a correction surface. Since the biharmonic equation is satisfied in the interpolation section other than measurement point 54, the correction surface S(x,y) can be obtained by the following equation (4). Furthermore, since an actual measurement value is obtained at measurement point 54, the correction surface can be obtained by the following equation (5).

[0096]

number

number

[0097] Here, the coordinates of the jth measurement point (j is an integer equal to or greater than 1) are (xj , y j ) and the difference value is dz j The correction data calculation unit 46 calculates α using the formulas (4) and (5). j The corrected curved surface S(x, y) is a smooth curved surface that passes through the height indicated by the measurement point 54.

[0098] Equation (6) shows the displacement u in the one-dimensional case, and equation (7) shows the displacement u in the two-dimensional case. j , y j ), when a force fi is applied to the thin plate, the displacement u follows the following equation (7). Note that this is similar to the equation above, so it is possible to appropriately correct any discrepancies with the analytical results resulting from the displacement.

[0099]

number

number

[0100] As described above, the correction data calculation unit 46 calculates the correction data from the difference value using the Green's function of the biharmonic operator. The correction data calculation unit 46 approximates the correction surface using a function that satisfies the biharmonic equation as a basis. By using the biharmonic equation, the correction surface can be approximated efficiently. Specifically, by using the Green's function of the biharmonic operator, an appropriate correction surface can be obtained without performing complex calculations.

[0101] The estimation unit 47 calculates estimated data for estimating the height of the sample by correcting the deflection data using the correction data. Specifically, the estimated data is calculated by adding the correction data to the deflection data. The surface indicated by the estimated data is regarded as a predicted surface. The estimated data includes an estimated value for estimating the height of the measurement surface 53 of the sample 50. In other words, in the estimated data, the estimated value of the height is associated with an XY coordinate. The height indicated by the estimated data is also referred to as an estimated height.

[0102] 16 is a three-dimensional graph illustrating the estimated data estimated by the estimation unit 47 in the imaging device 2 according to embodiment 2, where the two horizontal axes indicate positions in the X-axis and Y-axis directions and the vertical axis indicates the amount of deformation. As shown in Fig. 16, the estimation unit 47 calculates the estimated data from the deflection data in Fig. 13 and the correction data in Fig. 15.

[0103] The drive control unit 43 adjusts the focus based on the estimated data to image the sample 50. Specifically, the drive control unit 43 adjusts the focus by changing the distance between the optical element and the sample 50 based on the height of the estimated data (estimated height). The drive control unit 43 drives the stage 10 so that the focal position moves along the predicted curved surface. This causes the focal position to move so as to follow the predicted curved surface. In addition to the operation of following the predicted curved surface, the drive control unit 43 can also perform autofocus. Specifically, the drive control unit 43 drives the stage 10 in the Z-axis direction, starting from the estimated height, to perform autofocus. To adjust the focus, the drive control unit 43 changes the distance between the objective lens 23 and the sample 50. This allows the focus to be adjusted without causing a large deviation between the focal position and the pattern-formed surface of the sample 50. Therefore, the focus can be adjusted appropriately and quickly. When performing autofocus, the Z position of the stage 10 may be measured using a measurement means other than the height information detection unit 30. This allows the image sensor 24 to capture an image of the sample 50 in focus without using the height information detection unit 30.

[0104] Next, a focus adjustment method according to the second embodiment will be described. Fig. 17 is a flow chart illustrating the focus adjustment method according to the second embodiment. As shown in step S21 of Fig. 17, height data of each of the plurality of measurement points 54 is acquired. For example, the height data of each of the plurality of measurement points 54 is acquired by the procedure of steps S11 to S15 of the focus adjustment method according to the first embodiment described above.

[0105] Next, as shown in step S22, deflection data is acquired. Specifically, the deflection data acquisition unit 44 acquires deflection data corresponding to the deflection of the sample 50 supported by the stage 10 having a plurality of support points. Note that step S22 may be performed before step S21 or may be performed in parallel with step S21.

[0106] Next, as shown in step S23, a difference value is calculated. Specifically, the difference value calculation unit 45 calculates a difference value between the height indicated by the height data and the height indicated by the deflection data at the plurality of measurement points 54.

[0107] Next, as shown in step S24, correction data is calculated. For example, the correction data calculation unit 46 calculates the correction data based on the difference value. Next, as shown in step S25, estimation data is calculated. The estimation unit 47 corrects the deflection data using the correction data, thereby estimating the height of the sample 50.

[0108] Next, as shown in step S26, the focus is adjusted. The drive control unit 43 adjusts the focus based on the estimated data in order to image the sample 50. In this way, the imaging device 2 can adjust the focus.

[0109] Next, the effects of this embodiment will be described. In this embodiment, the difference value calculation unit 45 calculates the difference between the height indicated by the deflection data and the height indicated by the height data. The height indicated by the deflection data is a value calculated by simulation. On the other hand, the height indicated by the height data is an actual measurement value. The correction data calculation unit 46 calculates correction data based on the difference value. The correction data becomes a correction surface indicating the difference in deformation amount between the calculated deflection data and the actual measured height data. The estimation unit 47 calculates estimated data by correcting the deflection data with the correction data. The estimation unit 47 corrects the reference curved surface with the correction curved surface. In this way, the processing device 40a can obtain an appropriate predicted curved surface with a small amount of calculation. The drive control unit 43 performs autofocus using the height of the estimated data as a reference. Therefore, defocusing can be suppressed.

[0110] According to this embodiment, even when the number of measurement points 54 is small, the height of the measurement surface 53 can be estimated with high accuracy. In other words, because the predicted surface is not calculated directly from the heights of the measurement points 54, errors in the amount of deformation can be suppressed, and the height of the measurement surface 53 can be estimated with higher accuracy. Since autofocusing can be performed based on the estimated height, it is possible to prevent the focus position from shifting significantly. Therefore, the focus can be adjusted quickly and promptly. Furthermore, because the correction data calculation unit 46 uses a biharmonic equation, the correction surface can be calculated with a smaller number of measurement points. The estimation unit 47 can calculate the predicted surface with high accuracy.

[0111] In the above description, correction data is obtained using a biharmonic equation, but the correction surface may be obtained by surface approximation other than a biharmonic equation. For example, correction data may be calculated by surface approximation using a polynomial of degree two or higher. The approximation functions are preferably polynomials of degree four or higher for each of X and Y. When approximating using a polynomial, the number of measurement points required may be determined depending on the degree.

[0112] By using height detection by the height information detection unit 30 in combination with inspection, it is also possible to detect the structure of the sample 50. For example, if the sample 50 is a photomask, it is possible to detect a light-shielding film, a multilayer film, a low-reflection layer, etc., provided on the pattern-forming surface 52.

[0113] During AF, if there is a large error in height between the predicted curved surface and the pattern forming surface 52, the drive control unit 43 may perform control to reduce the error component. Specifically, there may be a localized error between the estimated height indicated by the predicted curved surface and the height information detected by the height information detection unit 30 that is equal to or greater than a threshold. In this way, if there is a large amount of focus deviation on the predicted curved surface, the drive control unit 43 may perform autofocus using a height that is deviated from the predicted curved surface by a predetermined value as a reference.

[0114] The processing devices 40 and 40a are not limited to being physically single devices. That is, the processing in the processing devices 40 and 40a may be distributed and performed by multiple devices. For example, the processing device that acquires the detection data from the image sensor 24 and the height information from the photodetector 34 and the processing device that performs the arithmetic processing may be physically different devices.

[0115] Although the embodiments of the present disclosure have been described above, the present disclosure includes appropriate modifications that do not impair the objects and advantages thereof, and is not limited to the above-described embodiments. Furthermore, the configurations in the first and second embodiments may be combined as appropriate.

[0116] The technical concept of the embodiment also includes the following focus adjustment program that causes a computer to execute the focus adjustment method of the embodiment.

[0117] acquiring measurement points set at a plurality of positions when the measurement surface of the sample is viewed from above; a step of controlling a position of the height information detection unit relative to the sample so that the height information detection unit, which detects height information indicating the height of the measurement surface, scans a measurement region including the vicinity of the measurement point and detects a plurality of pieces of height information in the measurement region; acquiring height data for each of the plurality of measurement points by using a mode value of the plurality of height information detected in the measurement area as the height information for the measurement point and acquiring height data including the position and the height information of the measurement point; adjusting a focus of an imaging unit that images the measurement surface based on the acquired height data of each of the plurality of measurement points; A focus adjustment program that causes a computer to execute the above.

[0118] Furthermore, the above-described focus adjustment program includes a set of instructions (or software code) that, when loaded into a computer, causes the computer to perform one or more functions described in the first and second embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disc (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals. [Explanation of symbols]

[0119] 1, 2 Imaging device 10 stages 11 Pedestal 12 Support pin 20 Imaging unit 21 Light source 22 Beam Splitter 23 Objective Lens 24 Image sensor 30 Height information detection unit 31 AF light source 32, 33 lenses 34 Photodetector 34a, 34b Photodiodes 40, 40a Processing equipment 41 Measurement point acquisition section 42 Height data acquisition unit 43 Drive control unit 44 Deflection data acquisition section 45 Differential value calculation unit 46 Correction data calculation section 47 Estimation part 50, 50a samples 51 patterns 52, 52a Pattern forming surface 53 Measurement surface 54, 54a, 54b measurement points 55 areas 56 Central area 57 Surrounding Area 58 positions 59 Measurement area 101 areas L11 illumination light L12 reflected light L21, L22, L23 light beams

Claims

1. a measurement point acquisition unit that acquires measurement points set at a plurality of positions when the measurement surface of the sample is viewed from above; a height information detection unit that detects height information indicating the height of the measurement surface; a drive control unit that controls the position of the height information detection unit relative to the sample so that the height information detection unit scans a measurement region including the vicinity of the measurement point and detects a plurality of pieces of height information in the measurement region; a height data acquisition unit that acquires height data for each of the plurality of measurement points by using a mode value of the plurality of height information detected in the measurement area as the height information for the measurement point and acquiring height data including the position and the height information of the measurement point; an imaging unit that images the measurement surface; Equipped with the drive control unit adjusts the focus of the imaging unit based on the acquired height data of each of the plurality of measurement points. Imaging device.

2. the measurement point acquisition unit uses a mask having a central region and a peripheral region as the sample, and acquires the plurality of measurement points set in the central region where a pattern is formed; the drive control unit controls the height information detection unit to scan the measurement area including the edge of the pattern in the central area in a direction intersecting a direction in which the edge of the pattern extends. The imaging device according to claim 1 .

3. the measurement point acquisition unit acquires the plurality of measurement points set in the surrounding area; the drive control unit controls the position of the height information detection unit so that the height information detection unit detects the height information at the measurement point in the peripheral area; the height data acquisition unit acquires height data including the positions of the measurement points in the surrounding area and the height information detected at the measurement points in the surrounding area, thereby acquiring height data for each of the plurality of measurement points in the surrounding area. The imaging device according to claim 2 .

4. a stage that supports the sample at a plurality of support points; a deflection data acquisition unit that acquires deflection data corresponding to the deflection of the sample supported by the stage; a difference value calculation unit that calculates a difference value between a height indicated by the height data and a height indicated by the deflection data at the plurality of measurement points; a correction data calculation unit that calculates correction data based on the difference value; an estimation unit that calculates estimation data for estimating the height of the sample by correcting the deflection data using the correction data; Furthermore, the drive control unit adjusts the focus based on the estimated data in order to image the sample. The imaging device according to any one of claims 1 to 3.

5. the correction data calculation unit calculates the correction data using a biharmonic equation. The imaging device according to claim 4 .

6. an illumination light source that generates illumination light; an optical element that collects light from the sample illuminated with the illumination light; a detector that detects light from the optical element; Furthermore, the drive control unit performs autofocus by changing the distance between the optical element and the sample based on the height of the estimated data. The imaging device according to claim 4 .

7. The deflection data is obtained by numerical analysis. The imaging device according to claim 4 .

8. acquiring measurement points set at a plurality of positions when the measurement surface of the sample is viewed from above; a step of controlling a position of the height information detection unit relative to the sample so that the height information detection unit, which detects height information indicating the height of the measurement surface, scans a measurement region including the vicinity of the measurement point and detects a plurality of pieces of height information in the measurement region; acquiring height data for each of the plurality of measurement points by using a mode value of the plurality of height information detected in the measurement area as the height information for the measurement point and acquiring height data including the position and the height information of the measurement point; adjusting a focus of an imaging unit that images the measurement surface based on the acquired height data of each of the plurality of measurement points; A focus adjustment method comprising:

9. In the step of acquiring each of the set measurement points, a mask having a central region and a peripheral region is used as the sample, and the plurality of measurement points set in the central region on which a pattern is formed are acquired; In the step of controlling the position of the height information detection unit with respect to the sample, controlling the height information detection unit to scan the measurement area including the edge of the pattern in the central area in a direction intersecting a direction in which the edge of the pattern extends; The focus adjusting method according to claim 8 .

10. In the step of acquiring each of the set measurement points, acquiring the plurality of measurement points set in the peripheral region; In the step of controlling the position of the height information detection unit with respect to the sample, controlling the height information detection unit to detect the height information at the measurement point in the peripheral area; In the step of acquiring height data of each of the plurality of measurement points, acquiring height data including the positions of the measurement points in the peripheral area and the height information detected at the measurement points in the peripheral area, thereby acquiring height data for each of the plurality of measurement points in the peripheral area; The focus adjusting method according to claim 9 .

11. acquiring deflection data corresponding to deflection of the sample supported by a stage having a plurality of support points; calculating a difference value between a height indicated by the height data and a height indicated by the deflection data at the plurality of measurement points; calculating correction data based on the difference value; calculating estimated data for estimating the height of the sample by correcting the deflection data using the correction data; Furthermore, In the step of adjusting the focus of an imaging unit that images the measurement surface, adjusting the focus using the estimated data; The focus adjusting method according to any one of claims 8 to 10.

12. In the step of calculating the correction data, The correction data is calculated using a biharmonic equation. The focus adjusting method according to claim 11.

13. In the step of controlling the position of the height information detection unit with respect to the sample, a detector detects light from the sample illuminated with illumination light via an optical element; In the step of adjusting the focus of an imaging unit that images the measurement surface, Autofocusing is performed by changing the distance between the optical element and the sample based on the height of the estimated data. The focus adjusting method according to claim 11.

14. In the step of acquiring the deflection data, The deflection data is obtained by numerical analysis. The focus adjusting method according to claim 11.

Images