JP2017194273A - Surface inspection method, surface inspection device and surface inspection program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect abnormality in the height of a mirror surface.SOLUTION: An image acquisition unit 11 acquires a first captured image group obtained by capturing an image in which an illumination pattern whose luminous power changes in the form of a sinusoidal wave is projected to the measurement surface on a mirror surface of a sample being inspected a number of times while changing the phase of the illumination pattern, and a second captured image group obtained by capturing an image in which an illumination pattern is projected to the measurement surface on a mirror surface of a reference sample that serves as reference to the sample being inspected a number of times while changing the phase of the illumination pattern. An abnormality detection unit 12 calculates first phase information that indicates a per-pixel phase on the basis of the first captured image group, and also calculates second phase information that indicates a per-pixel phase on the basis of the second captured image group, and detects abnormality in the height of the measurement surface of the sample being inspected on the basis of the result of comparison of the first phase information with the second phase information.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface inspection method, a surface inspection apparatus, and a surface inspection program.

  In recent years, the surface shape of an inspection object has been measured in a non-contact manner. Such surface shape measurement results are used, for example, in applications such as automatically inspecting the presence or absence of surface scratches or distortions. A phase shift method is known as a method for measuring the surface shape.

  In the phase shift method, for example, a measurement surface is irradiated with a sinusoidal illumination pattern, a plurality of images of the measurement surface are captured while changing the phase of the illumination pattern, and a phase angle is calculated from each captured image. When the measurement surface of the inspection object is a rough surface, for example, there is a method of measuring the height of the measurement surface based on the principle of triangulation using the calculated phase angle.

  On the other hand, when the surface of the inspection object is a mirror surface, for example, the measurement surface is roughened by spreading powder on the measurement surface, and the surface is roughened by using diffuse reflection of irradiated light on the measurement surface. There is a method of measuring the surface shape as in the case of. However, this method has a problem that the inspection object is contaminated.

  On the other hand, it is considered to measure the surface shape of a test object having a mirror surface by a phase shift method using a sinusoidal illumination pattern. For example, a method of measuring a surface shape using two cameras that capture images of a measurement surface from different directions has been proposed. A method for detecting a surface defect based on a first-order differential image of a phase image has been proposed.

JP2013-167464A JP 2007-322162 A JP 2014-20870 A

  However, the above-described method using the first-order differential image of the phase image can only detect a specific abnormal part such as a part where the inclination changes on a flat surface, and cannot determine whether or not the surface height itself is abnormal. There's a problem.

  In one aspect, an object of the present invention is to provide a surface inspection method, a surface inspection apparatus, and a surface inspection program capable of detecting an abnormality in mirror surface height.

  In one proposal, a surface inspection method is provided in which a computer performs the following process. In this surface inspection method, the computer obtains an image obtained by projecting an illumination pattern in which the amount of light changes sinusoidally on the specular measurement surface of the first sample by changing the phase of the illumination pattern a plurality of times. By imaging the image of the illumination pattern projected onto the mirror measurement surface of the first sampled image group and the second sample serving as a reference for the first sample by changing the phase of the illumination pattern multiple times The obtained second captured image group is acquired. The computer calculates first phase information indicating the phase of each pixel based on the first captured image group, and second phase information indicating the phase of each pixel based on the second captured image group. Is calculated. Then, the computer detects an abnormality in the height of the measurement surface in the first sample based on the comparison result between the first phase information and the second phase information.

Moreover, in one proposal, a surface inspection apparatus that performs the same processing as the above-described surface inspection method is provided.
Furthermore, in one proposal, there is provided a surface inspection program that causes a computer to execute the same processing as the surface inspection method described above.

  In one aspect, an abnormal mirror surface height can be detected.

It is a figure which shows the structural example and processing example of the surface inspection apparatus which concern on 1st Embodiment. It is a 1st figure for demonstrating the calculation method of the phase information based on a captured image. It is a 2nd figure for demonstrating the calculation method of the phase information based on a captured image. It is a figure which shows the structural example of the test | inspection system which concerns on 2nd Embodiment. It is a figure which shows the hardware structural example of a control apparatus. It is a block diagram which shows the structural example of the processing function of a control apparatus. It is a figure for demonstrating the quality determination method of height. It is a figure for demonstrating the calibration of height. It is a flowchart (the 1) which shows the example of the procedure of the whole inspection control process. It is a flowchart (the 2) which shows the example of the procedure of the whole test | inspection control process. It is a flowchart which shows the example of the calculation procedure of a phase image. It is a figure for demonstrating the calibration of the height in 3rd Embodiment. It is a figure for demonstrating the determination method of the increase rate of a phase. It is a flowchart (the 1) which shows the example of the procedure of the whole inspection control process. It is a flowchart (the 2) which shows the example of the procedure of the whole test | inspection control process.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram illustrating a configuration example and a processing example of the surface inspection apparatus according to the first embodiment. A surface inspection apparatus 10 illustrated in FIG. 1 is an apparatus that can detect an abnormality in height on a measurement surface of a mirror surface included in a test sample based on a measurement result by a measurement unit including an illumination light source 2 and an imaging device 3. . In the measurement unit, the illumination light source 2 irradiates the upper surface (measurement surface) of the sample 1 with an illumination pattern whose light amount changes in a sine wave shape. The imaging device 3 captures an image in which an illumination pattern is projected on the measurement surface of the sample 1. Since the measurement surface is a mirror surface, a virtual image of the illumination pattern irradiated by the illumination light source 2 is reflected in the imaging device 3.

  The illumination pattern may be a pattern in which the amount of light changes sinusoidally with respect to one direction on the irradiation surface of the illumination light source 2. In the present embodiment, the illumination pattern is a pattern in which the amount of light changes sinusoidally in one direction and the amount of light in the direction orthogonal thereto is the same. Moreover, the illumination light source 2 can change the phase of the illumination pattern to irradiate.

  For example, when the measurement surface of the sample 1 is a horizontal plane (that is, the height is uniformly the same), the imaging device 3 can change the illumination pattern irradiated from the illumination light source 2 with respect to the vertical direction and the horizontal direction. It is configured to be able to capture images without distortion. Such a configuration is realized by using, for example, a shift lens. With this configuration, in the present embodiment, when the measurement surface of the sample 1 is a horizontal plane, the illumination pattern is changed in a sine wave shape with respect to the horizontal direction of the captured image, and the vertical light amount is the same. It is possible to image as a pattern.

  In addition, as the sample 1 to be imaged by the imaging device 3, a reference sample serving as a reference for the test sample is used in addition to the test sample that is a target for detecting an abnormality in height. The reference sample is a non-defective product corresponding to the test sample in which the height of the measurement surface is correctly formed.

  The surface inspection apparatus 10 includes an image acquisition unit 11 and an abnormality detection unit 12. The processing of the image acquisition unit 11 and the abnormality detection unit 12 is realized by, for example, a processor included in the surface inspection apparatus 10 executing a predetermined program.

  The image acquisition unit 11 acquires a captured image captured by the imaging device 3. Specifically, the image acquisition unit 11 captures a first captured image group obtained by capturing an image obtained by projecting the illumination pattern on the measurement surface of the test sample a plurality of times while changing the phase of the illumination pattern. get. Further, the image acquisition unit 11 acquires a second captured image group obtained by capturing an image obtained by projecting the illumination pattern on the measurement surface of the reference sample a plurality of times while changing the phase of the illumination pattern.

  For example, four illumination patterns 21a to 21d having different phases are used. And the captured images 31a-31d are imaged in the state which irradiated the illumination patterns 21a-21d to the test sample, respectively. Further, the captured images 32a to 32d are captured in a state where the illumination patterns 21a to 21d are respectively irradiated on the reference sample. The image acquisition unit 11 acquires captured images 31a to 31d as the first captured image group, and acquires captured images 32a to 32d as the second captured image group.

  The abnormality detection unit 12 calculates first phase information indicating a phase for each pixel based on the captured images 31a to 31d. Further, the abnormality detection unit 12 calculates second phase information indicating the phase for each pixel based on the captured images 32a to 32d. The abnormality detection unit 12 compares the first phase information and the second phase information, and detects an abnormality in the height of the measurement surface in the test sample based on the comparison result.

Here, in the surface inspection apparatus 10, the phase information is calculated using the phase shift method. Hereinafter, a method for calculating phase information using the phase shift method will be described with reference to FIGS.
FIG. 2 is a first diagram for explaining a method of calculating phase information based on a captured image. FIG. 3 is a second diagram for explaining a method for calculating phase information based on a captured image.

  FIG. 2 shows a case where a sample 1a having a horizontal measurement surface is imaged. As described above, the imaging device 3 includes the virtual image 2a of the illumination pattern irradiated from the illumination light source 2 onto the measurement surface of the sample 1a. An image 33 illustrated in FIG. 2 is an example of an image captured in such a state. Like this image 33, an image is observed in which the luminance changes in a sine wave shape in the horizontal direction (X-axis direction) and the luminance in the vertical direction (Y-axis direction) is the same.

  In the phase shift method, a plurality of captured images are captured by changing the phase of the illumination pattern. Typically, four captured images in which the phase of the illumination pattern is shifted by π / 2 (rad) are captured. Graph 5 in FIG. 3 shows an example of the relationship between the position in the X-axis direction and the brightness in each of the four captured images.

The brightness I1, I2, I3, and I4 at a certain point on the captured image is expressed by the following equations (1-1) to (1-4). The brightnesses I1, I2, I3, and I4 correspond to cases where the phase shift amounts of the illumination patterns are 0, π / 2, π, and 3π / 2, respectively.
I1 = A + Bcos (φ) (1-1)
I2 = A + Bcos (φ + π / 2) (1-2)
I3 = A + Bcos (φ + π) (1-3)
I4 = A + Bcos (φ + 3π / 2) (1-4)
From the equations (1-1) to (1-4), when the phase shift amount is 0, the phase φ of the illumination pattern corresponding to the brightness observed in one pixel is expressed by the following equation (2). It is expressed as follows.
φ = atan {(I2-I4) / (I1-I3)} (2)
The straight line shown in the graph 6 of FIG. 3 shows the change of the phase of the X-axis direction based on Formula (2). However, the phase change directly obtained from the equation (2) is as shown by the broken line in the graph 6. The abnormality detection unit 12 of the surface inspection apparatus 10 calculates a phase value such as a straight line in the graph 6 by continuating the phase values obtained as indicated by the broken lines. Such a phase value continuation process is called “unwrap”. In the following description, the phase calculated based on the captured image using the phase shift method indicates an unwrapped phase.

  Here, as the height of the measurement surface of the sample 1a is higher, the cycle of the illumination pattern appearing in the captured image is longer, and conversely, as the height is lower, the cycle of the illumination pattern appearing in the captured image is shorter. Therefore, the phase change rate in the graph 6 changes according to the height of the measurement surface of the sample 1a, and the phase φ of each pixel represented by the equation (2) also corresponds to the height of the measurement surface of the sample 1a. Change. The surface inspection apparatus 10 according to the present embodiment uses this principle to detect an abnormality in height on the measurement surface of the test sample.

Hereinafter, the description will be returned to FIG.
When the above phase is calculated based on a plurality of captured images obtained using a plurality of illumination patterns 21a to 21d having different phases, the phase φ is a value corresponding to the height of the measurement surface of the sample. Therefore, the abnormality detection unit 12 of the surface inspection apparatus 10 is based on the first phase information calculated based on the captured images 31a to 31d obtained by imaging the test sample and the captured images 32a to 32d obtained by imaging the reference sample. The calculated second phase information is compared. Note that the phase information can be obtained, for example, as a phase image in which the phase φ calculated for each pixel is plotted, and this indicates the phase distribution in the captured image. In the graph 4 shown in FIG. 1, a curve 4a indicates first phase information calculated based on the captured images 31a to 31d, and a curve 4b indicates a second phase calculated based on the captured images 32a to 32d. Indicates information.

  If the height of the measurement surface of the test sample does not match the reference sample even at one location, the first phase information and the second phase information do not match. For this reason, the abnormality detection unit 12 can detect that there is an abnormality in the height of the test sample when the phase information does not match. For example, the abnormality detection unit 12 compares the first phase information and the second phase information for each pixel in consideration of the influence of measurement errors and the like, and a predetermined number of pixels whose phase difference exceeds a predetermined threshold value. If more than one (however, one or more) is detected, the test sample may be determined to be defective. In addition, the abnormality detection unit 12 can determine, for example, a pixel whose phase difference exceeds a threshold as an abnormal portion of the height on the measurement surface of the test sample.

  As described above, according to the surface inspection apparatus 10 according to the first embodiment, it is possible to detect an abnormality in the height of the sample surface on the mirror surface. The above-described height abnormality detection method by the surface inspection apparatus 10 is to detect an abnormality in the height of the test sample by comparison with a non-defective product. For this reason, for example, unlike a method of detecting a defective region that satisfies a specific condition such that the phase increase rate changes, it is possible to determine whether a certain place is abnormal regardless of the change in the phase increase rate. Moreover, even if the measurement surface of the test sample is flat, an abnormality in height can be detected. For example, even when the height of the entire measurement surface of the test sample differs from the reference sample by a certain amount, it can be detected that the height is abnormal.

Further, according to the first embodiment, since inspection can be performed using only one imaging device 3, the configuration for inspection can be simplified, and the cost and scale of the inspection system can be reduced.
Furthermore, for example, as a method for measuring the surface shape of the mirror surface, there is an optical interference method. Although this method can measure in sub-micron order, the measurement area is limited to about several millimeters square, and measurement cannot be performed when the height change is large (for example, 1 mm or more). According to the first embodiment, height abnormalities can be detected at once for a wider region such as at least several tens of millimeters square or more. In addition, an abnormality in height can be detected with a simpler system configuration than the optical interferometry.

[Second Embodiment]
Next, as a second embodiment, an inspection system capable of measuring not only whether or not the surface height of the test sample is abnormal, but also a height difference value indicating how much it differs from the normal height. Will be described.

  FIG. 4 is a diagram illustrating a configuration example of an inspection system according to the second embodiment. The inspection system illustrated in FIG. 4 includes a stage 51, an illumination light source 52, an imaging device 53, a stage controller 54, an illumination controller 55, an imaging controller 56, a control device 100, and an output device 100a.

  The stage 51 has a horizontal upper surface on which the sample 60 is disposed. The stage 51 can be moved up and down by a moving mechanism (not shown). As will be described later, on the upper surface of the stage 51, in addition to a test sample to be inspected, a non-defective sample (reference sample) that is a reference for pass / fail judgment, a plane mirror that is a reference for height calculation is arranged. There is a case.

  The illumination light source 52 irradiates the sample 60 on the stage 51 with an illumination pattern in which the amount of light in one direction of the illumination light source 52 changes in a sine wave shape. The illumination light source 52 can change the phase of the illumination pattern under the control of the illumination controller 55. The illumination light source 52 can be realized as a display device such as a projector or a liquid crystal display. The imaging device 53 images the sample 60 on the stage 51. The height measurement surface of the sample 60 is a mirror surface, and the imaging device 53 captures a virtual image of the illumination pattern irradiated on the measurement surface of the sample 60. The imaging device 53 includes a shift lens, for example, so that the measurement surface of the sample 60 can be imaged without causing distortion.

  It should be noted that the upper and lower limits of the height of the stage 51, the size of the upper surface of the stage 51, and the size of the irradiation surface of the illumination light source 52 are the same as the illumination pattern from the illumination light source 52 regardless of the height of the stage 51. It is set so as to be reflected by 60 and reflected in the imaging device 53.

  The stage controller 54 moves the stage 51 up and down under the control of the control device 100 to control the height of the stage 51. The illumination controller 55 changes the phase of the illumination pattern irradiated on the illumination light source 52 under the control of the control device 100. The imaging controller 56 controls the imaging operation of the imaging device 53 under the control of the control device 100 and supplies the captured image obtained by the imaging to the control device 100.

  The control device 100 comprehensively controls the entire inspection system. Based on the captured image acquired from the imaging controller 56, the control device 100 determines whether there is an abnormality in the height of the measurement surface of the sample 60 and calculates a difference value from the normal height. The control device 100 is an example of the surface inspection device 10 shown in FIG. The output device 100a outputs the inspection result by the control device 100. The output device 100a can be realized as a display device, for example.

FIG. 5 is a diagram illustrating a hardware configuration example of the control device. The control device 100 is realized, for example, as a computer as shown in FIG.
The entire control device 100 is controlled by the processor 101. The processor 101 may be a multiprocessor. The processor 101 is, for example, a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), a GPU (Graphics Processing Unit), or a PLD (Programmable Logic Device). . The processor 101 may be a combination of two or more elements among CPU, MPU, DSP, ASIC, GPU, and PLD.

A RAM (Random Access Memory) 102 and a plurality of peripheral devices are connected to the processor 101 via a bus 108.
The RAM 102 is used as a main storage device of the control device 100. The RAM 102 temporarily stores at least part of an OS (Operating System) program and application programs to be executed by the processor 101. The RAM 102 stores various data necessary for processing by the processor 101.

  Peripheral devices connected to the bus 108 include an HDD (Hard Disk Drive) 103, a graphic processing device 104, an input interface 105, a reading device 106, and a communication interface 107.

  The HDD 103 is used as an auxiliary storage device of the control device 100. The HDD 103 stores an OS program, application programs, and various data. As the auxiliary storage device, other types of nonvolatile storage devices such as SSD (Solid State Drive) can be used.

  A display device 104 a is connected to the graphic processing device 104. The graphic processing device 104 displays an image on the screen of the display device 104a in accordance with an instruction from the processor 101. Examples of the display device 104a include a liquid crystal display and an organic EL (ElectroLuminescence) display. The display device 104a is an example of the output device 100a in FIG.

  An input device 105 a is connected to the input interface 105. The input interface 105 transmits a signal output from the input device 105a to the processor 101. Examples of the input device 105a include a keyboard and a pointing device. Examples of pointing devices include a mouse, a touch panel, a tablet, a touch pad, and a trackball.

  A portable recording medium 106 a is detached from the reading device 106. The reading device 106 reads the data recorded on the portable recording medium 106 a and transmits it to the processor 101. Examples of the portable recording medium 106a include an optical disk, a magneto-optical disk, and a semiconductor memory.

The communication interface 107 transmits / receives data to / from the stage controller 54, the illumination controller 55, and the imaging controller 56.
With the hardware configuration described above, the processing function of the control device 100 can be realized.

  FIG. 6 is a block diagram illustrating a configuration example of processing functions of the control device. The control device 100 includes a control unit 121, a phase calculation unit 122, a pass / fail determination unit 123, a height calculation unit 124, and a storage unit 125. The processes of the control unit 121, the phase calculation unit 122, the pass / fail determination unit 123, and the height calculation unit 124 are realized by the processor 101 executing a predetermined program, for example. The storage unit 125 is realized as a storage area of the RAM 102, for example.

  The control unit 121 comprehensively controls the entire sample inspection process performed by the control device 100. For example, the control unit 121 sets shooting conditions and instructs the imaging controller 56 to cause the imaging device 53 to capture an image. The imaging condition setting process includes a process for instructing the illumination controller 55 to set the phase of the illumination pattern to be irradiated to the illumination light source 52 and a process for instructing the stage controller 54 to set the height of the stage 51. The control unit 121 receives the captured image captured by the imaging device 53 from the imaging controller 56 and stores it in the storage unit 125.

The phase calculation unit 122 calculates the phase of each pixel based on a plurality of captured images obtained by imaging the measurement surface of the sample using illumination patterns having different phases.
The pass / fail determination unit 123 determines whether the measurement surface of the test sample is high based on the phase calculated based on the captured image obtained by imaging the reference sample and the phase calculated based on the captured image obtained by imaging the test sample. A position where the height is abnormal is detected. Moreover, the quality determination part 123 may determine the quality of the test sample based on these phases. For example, the pass / fail determination unit 123 may determine that the test sample is defective when a position with an abnormal height is detected even at one location from the measurement surface of the test sample.

  The height calculation unit 124 includes a measurement image of the test sample based on a phase calculated based on a captured image obtained by imaging the plane mirror, a captured image obtained by imaging the reference sample, and a captured image obtained by imaging the test sample. A height difference value at a position where the height is determined to be abnormal is calculated.

The storage unit 125 stores various data used in the processing of the control device 100 such as a captured image and a coefficient of a mathematical formula for calculating a height difference value.
Next, FIG. 7 is a figure for demonstrating the quality determination method of height. In the inspection system of the present embodiment, the phase for each of the reference sample 61 and the test sample 62 is calculated using the phase shift method, as in the first embodiment.

  First, an illumination pattern is irradiated from the illumination light source 52 in a state where the reference sample 61 is arranged on the stage 51, and imaging by the imaging device 53 is performed. At this time, imaging is performed each time while shifting the phase of the illumination pattern by π / 2 (rad). The control unit 121 of the control device 100 passes the captured images 71a, 71b, 71c, and 71d captured when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2 via the imaging controller 56, respectively. Receive.

  In the inspection system, the illumination pattern is irradiated from the illumination light source 52 in a state where the test sample 62 is arranged on the stage 51, and imaging is performed by the imaging device 53. At this time, as described above, imaging is performed each time while shifting the phase of the illumination pattern by π / 2 (rad). The control unit 121 receives the captured images 72 a, 72 b, 72 c, and 72 d captured when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2 via the imaging controller 56.

  The phase calculation unit 122 calculates a phase for each pixel according to the above-described equation (2) based on the captured images 71a, 71b, 71c, and 71d. Here, as an example, it is assumed that a phase image PA in which phase values are plotted for each pixel of the captured image is calculated. The plotted phase is an unwrapped phase.

  The phase calculation unit 122 calculates a phase for each pixel according to the above-described equation (2) based on the captured images 72a, 72b, 72c, and 72d. Here, as an example, it is assumed that the phase image PB in which the phase value is plotted for each pixel of the captured image is calculated. The plotted phase is an unwrapped phase.

  The pass / fail judgment unit 123 compares the phase value of the phase image PA with the phase value of the phase image PB for each pixel. If the reference sample 61 and the test sample 62 have the same height at a position on the measurement surface, the phase value of the pixel corresponding to that position is also the same. On the other hand, when the height of the position is different, the phase value of the corresponding pixel is also different.

  The pass / fail determination unit 123 determines the test sample 62 as a defective product when a predetermined number or more of pixels having a phase value difference exceeding a predetermined threshold value are detected. The threshold value used for this determination is determined in consideration of the influence of measurement error, for example. In addition, the pass / fail judgment unit 123 can also extract a pixel whose phase value difference exceeds a threshold value as an abnormal height location.

  In the example of FIG. 7, the measurement surface of the reference sample 61 is horizontal, but it is assumed that a recess is formed near the center of the measurement surface of the test sample 62. The broken line of the graph 81 shown in FIG. 7 shows the transition of the phase along the horizontal line near the center among the phases calculated based on the captured images 71a, 71b, 71c, 71d. On the other hand, the solid line in the graph 81 indicates the transition of the phase along the same horizontal line as described above among the phases calculated based on the captured images 72a, 72b, 72c, and 72d. By comparing these phases, it is detected that the height is abnormal in the concave region formed on the measurement surface of the test sample 62.

  Next, a method for calculating the height difference value at the position where the height abnormality has occurred will be described. As described above, the height difference value is a value indicating how much the height of the position differs from the correct height. In order to calculate the height difference value, first, “height calibration” for calculating a reference for calculating the height from the calculated phase information is executed.

  FIG. 8 is a diagram for explaining the height calibration. In the second embodiment, calibration is executed using a plane mirror having a constant upper surface height. In calibration, the height of the stage 51 on which the plane mirror 63 is arranged is changed in a plurality of stages, and imaging is performed using illumination patterns having different phases each time the height is changed. The height may be changed in two steps at the minimum.

  For example, as shown in the upper left of FIG. 8, the height of the upper surface of the plane mirror 63 (that is, the coordinate in the Z-axis direction) is set to z1. In this state, an illumination pattern is emitted from the illumination light source 52, and imaging by the imaging device 53 is performed. At this time, imaging is performed each time while shifting the phase of the illumination pattern by π / 2 (rad). The control unit 121 of the control device 100 passes the captured images 73a, 73b, 73c, and 73d captured when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2 via the imaging controller 56, respectively. Receive.

  Next, as shown in the lower left of FIG. 8, the height of the upper surface of the plane mirror 63 is set to z2. In the example of FIG. 8, it is assumed that z2 <z1. In this state, an illumination pattern is emitted from the illumination light source 52, and imaging by the imaging device 53 is performed. At this time, as described above, imaging is performed each time while shifting the phase of the illumination pattern by π / 2 (rad). The control unit 121 receives captured images 74 a, 74 b, 74 c, and 74 d captured when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2, respectively, via the imaging controller 56.

  The phase calculation unit 122 calculates the phase for each pixel according to the above-described equation (2) based on the captured images 73a, 73b, 73c, and 73d. Here, as an example, it is assumed that the phase image PC1 in which the phase value is plotted for each pixel of the captured image is calculated. The phase calculation unit 122 calculates a phase for each pixel according to the above-described equation (2) based on the captured images 74a, 74b, 74c, and 74d. Here, as an example, it is assumed that the phase image PC2 in which the phase value is plotted for each pixel of the captured image is calculated. The phases plotted in the phase images PC1 and PC2 are unwrapped phases.

  In the graph 82 shown in FIG. 8, a straight line 82a indicates a transition of the phase with respect to the X-axis direction among the phases calculated based on the captured images 73a, 73b, 73c, and 73d. A straight line 82b indicates a transition of the phase with respect to the X-axis direction among the phases calculated based on the captured images 74a, 74b, 74c, and 74d. Since the upper surface of the plane mirror 63 is horizontal, the phase increases at a constant increase rate with respect to the X-axis direction as in the straight lines 82a and 82b.

  Here, in the phase image PC1 calculated from the captured images 73a, 73b, 73c, and 73d, the increase rate of the phase in the X-axis direction is the same for all the pixels, and this increase rate is d1. Also in the phase image PC2 calculated from the captured images 74a, 74b, 74c, and 74d, the increase rate of the phase in the X-axis direction is the same for all pixels, and this increase rate is d2. If there is a relationship of z1> z2 as shown in FIG. 8, d1 <d2.

When a phase image is calculated from a captured image of a sample and the phase increase rate dx (i, j) in the X-axis direction at the coordinates (i, j) is obtained from the phase image, the coordinates on the measurement surface of the sample ( The height z (i, j) of the position corresponding to i, j) is calculated according to the following equation (3), for example.
z (i, j) = (z2-z1) * dx (i, j) / (d2-d1)-(z2-z1) * d1 / (d2-d1) + z1 (3)
The height calculation unit 124 of the control device 100 calculates the height x (i, j) according to the equation (3) based on the phase image PC1 calculated using the reference sample 61. Specifically, the phase increase rate with respect to the X-axis direction at the coordinates (i, j) in the phase image PC1 is substituted into the increase rate dx (i, j) in Expression (3). In addition, the height calculation unit 124 calculates the height x (i, j) according to the equation (3) based on the phase image PC2 calculated using the test sample 62. Specifically, the increase rate of the phase with respect to the X-axis direction at the coordinates (i, j) in the phase image PC2 is substituted into the increase rate dx (i, j) of Equation (3). The height calculator 124 subtracts the other height x (i, j) from the calculated one height x (i, j) to obtain the absolute height difference value at the coordinates (i, j). Can be calculated as a typical value.

Next, the procedure of the inspection control process in the control device 100 will be described using a flowchart.
9 to 10 are flowcharts illustrating an example of the procedure of the entire inspection control process.

[Step S11] A reference sample is set on the stage 51.
[Step S12] Under the control of the control unit 121, illumination patterns having different phases are emitted from the illumination light source 52, and an image is captured for each illumination pattern. The control unit 121 receives a captured image for each illumination pattern from the imaging controller 56 and stores it in the storage unit 125. The phase calculation unit 122 calculates a phase image PA based on each received captured image and stores the phase image PA in the storage unit 125.

[Step S13] A plane mirror is set on the stage 51.
[Step S14] The control unit 121 instructs the stage controller 54 to set the height of the stage 51 to one of a plurality of predetermined stages. The stage controller 54 sets the height of the stage 51 to the instructed height.

  [Step S15] Under the control of the control unit 121, illumination patterns having different phases are emitted from the illumination light source 52, and an image is captured for each illumination pattern. The control unit 121 receives a captured image for each illumination pattern from the imaging controller 56 and stores it in the storage unit 125. The phase calculation unit 122 calculates a phase image PCn corresponding to the nth height stage based on each received captured image, and stores the phase image PCn in the storage unit 125.

  In the present embodiment, the height of the stage 51 is changed to two stages (z1-z0) and (z2-z0). z0 is the thickness of the plane mirror. Thereby, step S15 is repeated twice, and the phase image PC1 corresponding to the height (z1-z0) and the phase image PC2 corresponding to the height (z2-z0) are calculated.

  [Step S16] The height calculator 124 calculates the phase increase rate dn in the X-axis direction at the pixels of the phase image PCn. In the present embodiment, the increase rate d1 is calculated from the phase image PC1, and the increase rate d2 is calculated from the phase image PC2.

  [Step S17] The controller 121 determines whether the height of the stage 51 has been set at all predetermined stages. If there is an unset stage, the process proceeds to step S14, and the control unit 121 performs control so that the height of the stage 51 is changed to the next stage. On the other hand, if all the stages have been set, the process of step S21 in FIG. 10 is executed.

  [Step S21] A test sample is set on the stage 51. Further, the control unit 121 instructs the stage controller 54 to set the height of the stage 51 to the same height as that in step S11. The stage controller 54 sets the height of the stage 51 to the instructed height.

  [Step S22] Under the control of the control unit 121, illumination patterns having different phases are emitted from the illumination light source 52, and an image is captured for each illumination pattern. The control unit 121 receives a captured image for each illumination pattern from the imaging controller 56 and stores it in the storage unit 125. The phase calculation unit 122 calculates a phase image PB based on each received captured image and stores it in the storage unit 125.

[Step S23] The control unit 121 selects a pixel to be processed.
[Step S24] The quality determination unit 123 refers to the information of the phase images PA and PB stored in the storage unit 125, and extracts the phase value corresponding to the pixel to be processed from the phase images PA and PB. The pass / fail judgment unit 123 calculates the difference between the phase values by subtracting the phase value extracted from the phase image PB from the phase value extracted from the phase image PA.

  [Step S25] The quality determination unit 123 determines whether or not the height of the pixel to be processed is abnormal depending on whether or not the calculated phase value difference exceeds a predetermined threshold. When the difference between the phase values exceeds the threshold, it is determined that the height is abnormal. When it is determined that the height is abnormal, the process of step S26 is executed. When it is determined that the height is not abnormal, the process of step S28 is executed.

  [Step S26] The height calculator 124 calculates the phase increase rate with respect to the X-axis direction in the pixel to be processed of the phase image PA. The height calculation unit 124 substitutes the calculated increase rate for the increase rate dx (i, j) in Expression (3) generated using the heights z1 and z2 and the increase rates d1 and d2. Thereby, the height zb1 at the position corresponding to the pixel to be processed on the measurement surface of the reference sample is calculated.

  In addition, the height calculation unit 124 calculates the phase increase rate with respect to the X-axis direction in the pixel to be processed of the phase image PB. The height calculation unit 124 substitutes the calculated increase rate for the increase rate dx (i, j) in Expression (3). Thereby, the height zb2 at the position corresponding to the pixel to be processed on the measurement surface of the test sample is calculated.

[Step S27] The height calculator 124 subtracts the height zb2 from the height zb1, thereby calculating a height difference value corresponding to the pixel to be processed.
[Step S28] The control unit 121 determines whether all pixels in the phase image have been processed. If there is an unprocessed pixel, the process proceeds to step S23, and an unprocessed pixel is selected. On the other hand, if all the pixels have been processed, the process of step S29 is executed.

  [Step S29] The control unit 121 outputs the inspection result of the test sample set in step S21 via the output device 100a. Specifically, the control unit 121 provides information indicating that the test sample is defective when the height is determined to be abnormal at a predetermined number of times or more (that is, at a predetermined number of pixels or more) in step S25. Output. In this case, the control unit 121 outputs a height difference value calculated for each pixel whose height is determined to be abnormal.

  [Step S30] The control unit 121 determines whether to end the inspection. For example, when an inspection is performed using another test sample, the process proceeds to step S21. On the other hand, when ending the inspection, the control unit 121 ends the process.

  FIG. 11 is a flowchart illustrating an example of a phase image calculation procedure. The process in FIG. 11 corresponds to the process in each of steps S12 and S15 in FIG. 9 and step S22 in FIG.

  [Step S41] The control unit 121 instructs the illumination controller 55 to set the phase of the illumination pattern to be emitted to the illumination light source 52. Each time step S41 is executed, it is instructed to shift the phase by π / 2. The illumination controller 55 causes the illumination light source 52 to irradiate the illumination pattern of the instructed phase.

  [Step S42] The control unit 121 instructs the imaging controller 56 to take an image. The imaging controller 56 causes the imaging device 53 to capture an image and transmits the obtained captured image to the control device 100. The control unit 121 receives the captured image and stores it in the storage unit 125.

  [Step S43] The control unit 121 determines whether or not illumination patterns having all predetermined phases have been set. If there is an unset illumination pattern, the process of step S41 is executed, and if all have been set, the process of step S44 is executed.

[Step S <b> 44] The phase calculation unit 122 calculates a phase image based on each captured image stored in the storage unit 125 and stores the phase image in the storage unit 125.
According to the second embodiment described above, it is possible to detect an abnormality in height on the mirror surface of the sample to be tested, as in the first embodiment. In addition to this, according to the second embodiment, when an abnormal position of the height is detected from the mirror surface of the test sample, the absolute deviation of the height of the position from the correct height is determined. It can be calculated as a typical numerical value.

[Third Embodiment]
Next, an inspection system according to the third embodiment will be described. The inspection system according to the third embodiment is obtained by changing a part of the inspection procedure in the second embodiment. For example, the third embodiment is different from the second embodiment in that calibration for obtaining a height difference value is performed using a reference sample instead of a plane mirror.

  The basic configuration of the hardware and processing functions of the inspection system according to the third embodiment is the same as that of the second embodiment. Therefore, an inspection system according to the third embodiment will be described below using the reference numerals in FIGS. 4 and 6.

  FIG. 12 is a diagram for explaining the calibration of the height according to the third embodiment. In the third embodiment, calibration is executed using the reference sample 61 instead of the plane mirror. In calibration, the height of the stage 51 on which the reference sample 61 is arranged is changed in a plurality of stages, and imaging is performed using illumination patterns having different phases each time the height is changed. The height may be changed in two steps at the minimum.

  In addition, about the reference | standard sample 61 used by this Embodiment, the horizontal area | region with constant height exists in at least one part of the measurement surface. Then, when a height abnormality is detected in a region corresponding to the horizontal region in the measurement surface of the test sample, the height difference at that position can be calculated.

  For example, as shown in the upper left of FIG. 12, the reference sample 61 is arranged on the stage 51, and the height of the stage 51 is set such that the height of the horizontal region on the measurement surface of the reference sample 61 is z1. If there are a plurality of horizontal regions on the measurement surface, for example, the height of the horizontal region having the largest area may be adjusted to be z1. In this state, an illumination pattern whose phase is shifted by π / 2 is emitted from the illumination light source 52, and imaging is performed by the imaging device 53 for each illumination pattern. Thereby, the captured images 75a, 75b, 75c, and 75d when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2 are captured.

  Next, as shown in the lower left of FIG. 12, the height of the stage 51 is set so that the height of the horizontal plane is z2. In the same manner as described above, an illumination pattern whose phase is shifted by π / 2 is emitted from the illumination light source 52, and an image is taken by the imaging device 53 for each illumination pattern. Thereby, the captured images 76a, 76b, 76c, and 76d when the phase shift amount of the illumination pattern is 0, π / 2, π, and 3π / 2 are captured.

  The phase calculation unit 122 calculates the phase for each pixel according to the above-described equation (2) based on the captured images 75a, 75b, 75c, and 75d. Here, as an example, it is assumed that the phase image PB1 in which the phase value is plotted for each pixel of the captured image is calculated. In addition, the phase calculation unit 122 calculates the phase for each pixel according to the above-described equation (2) based on the captured images 76a, 76b, 76c, and 76d. Here, as an example, it is assumed that the phase image PB2 in which the phase value is plotted for each pixel of the captured image is calculated. The phases plotted in the phase images PB1 and PB2 are unwrapped phases.

  In the graph 83 shown in FIG. 12, a line 83a indicates a transition of the phase with respect to the X-axis direction among the phases calculated based on the captured images 75a, 75b, 75c, and 75d. A line 83b indicates the transition of the phase with respect to the X-axis direction among the phases calculated based on the captured images 76a, 76b, 76c, and 76d.

  FIG. 13 is a diagram for explaining a method of determining the phase increase rate. The height calculator 124 determines the phase increase rates d1 and d2 to be applied to the above-described equation (3) based on the calculated phase images PB1 and PB2. Here, in the phase image calculated using the plane mirror, the increase rate of the phase in all the pixels is the same. However, the measurement surface of the reference sample 61 is not necessarily a horizontal plane with the same height as the plane mirror. For this reason, the phase increase rate may differ depending on the pixel.

  In FIG. 13, as an example, the increase rate of the phase in each partial region of the phase images PB1 and PB2 is plotted in the pixel. FIG. 13A shows a partial region of the phase image PB1, and FIG. 13B shows the same region of the phase image PB2. According to FIG. 13A, the phase image PB1 includes a region where the phase change rate is D1 and a region where D3. Further, according to FIG. 13B, the phase image PB2 includes a region where the phase change rate is D2 and a region where D4. This indicates that there are two horizontal regions having different heights on the measurement surface of the reference sample 61.

  When pixels having the same phase increase rate are continuous in both the phase images PB1 and PB2, it can be determined that these pixels exist in the horizontal region. When it is determined that the position for calculating the height difference value is in the horizontal region, the increase rate of the phase in that region can be substituted for d1 and d2 in Expression (3). However, when the phase increase rate of adjacent pixels is different, for example, at the boundary between two horizontal regions having different heights, the phase increase rate at that position is not suitable for calculating the height difference value. Therefore, the height calculation unit 124 calculates the height difference value while avoiding such a position.

Next, the procedure of the inspection control process in the control device 100 according to the third embodiment will be described using a flowchart.
14 to 15 are flowcharts illustrating an example of the procedure of the entire inspection control process. Here, only processing contents different from those in FIGS. 9 to 10 will be described, and description of other processing contents will be omitted.

First, in the process of FIG. 14, steps S14a to S17a are executed instead of steps S12 to S17 shown in FIG.
[Step S14a] The control unit 121 instructs the stage controller 54 to set the height of the stage 51 on which the reference sample is set to one of a plurality of predetermined stages. The stage controller 54 sets the height of the stage 51 to the instructed height.

  [Step S15a] Under the control of the control unit 121, illumination patterns having different phases are emitted from the illumination light source 52, and an image is captured for each illumination pattern. The control unit 121 receives a captured image for each illumination pattern from the imaging controller 56 and stores it in the storage unit 125. The phase calculation unit 122 calculates a phase image PAn corresponding to the nth height stage based on each received captured image, and stores the phase image PAn in the storage unit 125.

  In the present embodiment, it is assumed that the height of the stage 51 is changed to two stages (z1-z0 ′) and (z2-z0 ′). z0 'is the thickness of the reference sample in the horizontal region that is the height reference in the measurement surface of the reference sample. Thereby, step S15a is repeated twice, and the phase image PA1 corresponding to the height (z1-z0 ') and the phase image PA2 corresponding to the height (z2-z0') are calculated.

[Step S16a] The height calculation unit 124 calculates the rate of increase in phase with respect to the X-axis direction at each pixel of the phase image PAn.
[Step S17a] The control unit 121 determines whether or not the height of the stage 51 has been set in all predetermined stages. If there is an unset stage, the process proceeds to step S14a, and the control unit 121 controls the height of the stage 51 to be changed to the next stage. On the other hand, if all the stages have been set, the process of step S21a in FIG. 15 is executed.

  Next, in the process of FIG. 15, steps S21a and S24a are executed instead of steps S21 and S24 shown in FIG. 10, respectively, and steps S26a and S26b are executed instead of step S26.

  [Step S21a] A test sample is set on the stage 51. Further, the control unit 121 instructs the stage controller 54 to set the height of the stage 51 to (z1−z0 ′). The stage controller 54 sets the height of the stage 51 to the instructed height.

  [Step S24a] The pass / fail judgment unit 123 refers to the information of the phase images PA1 and PB stored in the storage unit 125, and extracts the phase value corresponding to the pixel to be processed from the phase images PA1 and PB. The pass / fail judgment unit 123 calculates the difference between the phase values by subtracting the phase value extracted from the phase image PB from the phase value extracted from the phase image PA1.

  [Step S26a] The height calculation unit 124 determines an increase rate value to be substituted into d1 and d2 in Expression (3). In this process, the height calculation unit 124 determines the increase rate value when the pixel to be processed is included in the horizontal region. On the other hand, when the pixel to be processed is not included in the horizontal region, the height calculation unit 124 skips the determination of the increase rate value and the processing of the next steps S26b and S27.

  The determination as to whether or not the pixel to be processed is included in the horizontal region is executed as follows, for example. The height calculation unit 124 corresponds to each of the pixel to be processed and two pixels adjacent to the pixel in the X-axis direction from the phase increase rate calculated from the phase image PA1 in step S16a. Extract the rate of increase. The height calculation unit 124 determines whether the increase rate at the pixel to be processed matches each increase rate at each adjacent pixel. At the same time, the height calculation unit 124 selects each of the pixel to be processed and two pixels adjacent to the pixel in the X-axis direction from the phase increase rate calculated from the phase image PA2 in step S16a. The rate of increase corresponding to is extracted. The height calculation unit 124 determines whether the increase rate at the pixel to be processed matches each increase rate at each adjacent pixel.

  The height calculation unit 124 determines that the pixel to be processed is included in the horizontal region when the increase rates match in all these determinations. In this case, the height calculation unit 124 determines the increase rate at the pixel to be processed, which is calculated from the phase image PA1, as a value to be substituted for d1 in Expression (3), and is calculated from the phase image PA2. The increase rate at the pixel to be processed is determined as a value to be substituted for d2 in Expression (3).

  [Step S26b] The height calculation unit 124 extracts an increase rate corresponding to the pixel to be processed from the phase increase rates calculated from the phase image PA1 in Step S16a. The height calculation unit 124 is extracted for the increase rate dx (i, j) of Expression (3) generated using d1 and d2 determined in step S26a and the heights z1 and z2. Substitute the rate of increase. Thereby, the height zb1 at the position corresponding to the pixel to be processed on the measurement surface of the reference sample is calculated.

  In addition, the height calculation unit 124 calculates the phase increase rate with respect to the X-axis direction in the pixel to be processed of the phase image PB. The height calculator 124 substitutes the calculated increase rate for the increase rate dx (i, j) in the same equation (3). Thereby, the height zb2 at the position corresponding to the pixel to be processed on the measurement surface of the test sample is calculated.

  Through the above processing, an abnormality in the height of the measurement surface of the test sample can be detected, and a height indicating how much the height at the position where the height is determined to be abnormal deviates from the correct height. The difference value can be calculated.

  Note that the processing functions of the apparatuses (the surface inspection apparatus 10 and the control apparatus 100) described in the above embodiments can be realized by a computer. In that case, a program describing the processing contents of the functions that each device should have is provided, and the processing functions are realized on the computer by executing the program on the computer. The program describing the processing contents can be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include a magnetic storage device, an optical disk, a magneto-optical recording medium, and a semiconductor memory. Examples of the magnetic storage device include a hard disk device (HDD), a flexible disk (FD), and a magnetic tape. Optical disks include DVD (Digital Versatile Disc), DVD-RAM, CD-ROM (Compact Disc-Read Only Memory), CD-R (Recordable) / RW (ReWritable), and the like. Magneto-optical recording media include MO (Magneto-Optical disk).

  When distributing the program, for example, a portable recording medium such as a DVD or a CD-ROM in which the program is recorded is sold. It is also possible to store the program in a storage device of a server computer and transfer the program from the server computer to another computer via a network.

  The computer that executes the program stores, for example, the program recorded on the portable recording medium or the program transferred from the server computer in its own storage device. Then, the computer reads the program from its own storage device and executes processing according to the program. The computer can also read the program directly from the portable recording medium and execute processing according to the program. In addition, each time a program is transferred from a server computer connected via a network, the computer can sequentially execute processing according to the received program.

DESCRIPTION OF SYMBOLS 1 Sample 2 Illumination light source 3 Imaging device 4 Graph 4a, 4b Curve 10 Surface inspection apparatus 11 Image acquisition part 12 Abnormality detection part 21a-21d Illumination pattern 31a-31d, 32a-32d Captured image

Claims (6)

Computer
A first captured image group obtained by imaging an image in which an illumination pattern whose light amount changes in a sinusoidal shape on a mirror-like measurement surface of the first sample is imaged a plurality of times while changing the phase of the illumination pattern; A second image obtained by imaging an image obtained by projecting the illumination pattern onto a mirror measurement surface of a second sample serving as a reference for the first sample by changing the phase of the illumination pattern a plurality of times. Acquire a captured image group,
First phase information indicating a phase for each pixel is calculated based on the first captured image group, and second phase information indicating a phase for each pixel is calculated based on the second captured image group. ,
Detecting an abnormality in the height of the measurement surface of the first sample based on a comparison result between the first phase information and the second phase information;
Surface inspection method. In the detection, the phase included in the first phase information and the second phase information is compared for each pixel, and when a predetermined number or more of pixels whose phase difference exceeds a predetermined threshold is detected, Determining that the first sample is defective;
The surface inspection method according to claim 1. The computer is
An image obtained by projecting the illumination pattern onto the mirror surface of the plane mirror using a plane mirror having a mirror surface with a constant height is used to change the installation height of the plane mirror, and to change the illumination pattern for each of the same installation heights. Acquiring a third captured image group obtained by imaging a plurality of times while changing the phase;
Based on the third captured image group, third phase information indicating a phase for each pixel is calculated for each installation height,
Based on the first phase information, the second phase information, and the third phase information for each installation height, a normal value at a position where the height on the measurement surface of the first sample is abnormal Calculate the height difference value from
The surface inspection method according to claim 1, further comprising a treatment. In the acquisition, obtaining the second captured image group obtained for each installation height by changing the installation height of the second sample,
In the calculation, the second phase information is calculated for each installation height,
Further, the computer
Based on the first phase information and the second phase information for each installation height, the height difference value from the normal value at the position where the height of the measurement surface of the first sample is abnormal To calculate,
The surface inspection method according to claim 1, comprising a treatment. A first captured image group obtained by imaging an image in which an illumination pattern whose light amount changes in a sinusoidal shape on a mirror-like measurement surface of the first sample is imaged a plurality of times while changing the phase of the illumination pattern; A second image obtained by imaging an image obtained by projecting the illumination pattern onto a mirror measurement surface of a second sample serving as a reference for the first sample by changing the phase of the illumination pattern a plurality of times. An image acquisition unit for acquiring a captured image group;
First phase information indicating a phase for each pixel is calculated based on the first captured image group, and second phase information indicating a phase for each pixel is calculated based on the second captured image group. An abnormality detection unit that detects an abnormality in the height of the measurement surface of the first sample based on a comparison result between the first phase information and the second phase information;
A surface inspection apparatus. On the computer,
A first captured image group obtained by imaging an image in which an illumination pattern whose light amount changes in a sinusoidal shape on a mirror-like measurement surface of the first sample is imaged a plurality of times while changing the phase of the illumination pattern; A second image obtained by imaging an image obtained by projecting the illumination pattern onto a mirror measurement surface of a second sample serving as a reference for the first sample by changing the phase of the illumination pattern a plurality of times. Acquire a captured image group,
First phase information indicating a phase for each pixel is calculated based on the first captured image group, and second phase information indicating a phase for each pixel is calculated based on the second captured image group. ,
Detecting an abnormality in the height of the measurement surface of the first sample based on a comparison result between the first phase information and the second phase information;
Surface inspection program that executes processing.

Images