JP2010002274A - Surface inspection device and control method for quantity-of-light of illumination light - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface inspection device capable of enhancing the surface inspection precision of a substrate by detecting the quantity of illumination light for irradiating the substrate with high precision, and a control method for quantity-of-light of illumination light. <P>SOLUTION: The surface inspection device 1, having a holder 20 for placing and holding a wafer 10, an illumination optical system 30 for irradiating the surface of the wafer 10 placed and held on the holder 20 with illumination light, an imaging optical system 40 for detecting the light from the surface of the wafer 10 irradiated with the illumination light, and an image processor 50 for inspecting the presence of the flaw in the surface of the wafer 10 on the basis of the light detected by the imaging optical system 40, has the reflecting part 61 provided at the position receiving the illumination light of the holder 20, a quantity-of-light detecting part 62 for detecting the quantity of the regular reflected light from the reflecting part 61 irradiated with the illumination light, and a control unit 55 for controlling the quantity of the illumination light on the basis of the quantity of light detected by the quantity-of-light detecting part 62. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface inspection for inspecting the surface of a semiconductor wafer, a liquid crystal substrate or the like.

  In the manufacturing process of a semiconductor circuit element and a liquid crystal display element, a repetitive pattern (line and space pattern such as a wiring pattern) formed on the surface of a semiconductor wafer or a liquid crystal substrate (hereinafter generally referred to as “substrate”), etc. Inspection is performed. In an automated surface inspection apparatus, a substrate is placed on a tiltable holder, illumination light (non-polarized light) for inspection is irradiated on the surface of the substrate, and diffracted light generated from a repetitive pattern on the substrate (for example, The image of the substrate is captured on the basis of the first-order diffracted light), and the abnormal portion of the repetitive pattern is specified based on the contrast of the image. Furthermore, such a surface inspection apparatus can inspect a repetitive pattern or the like having a different repetitive pitch on the substrate by adjusting the tilt of the holder (see, for example, Patent Document 1).

  As a technique for inspecting a repetitive pattern formed on the surface of a substrate, in addition to inspection using diffracted light as described above (hereinafter, such inspection is referred to as diffraction inspection), inspection using specularly reflected light (hereinafter referred to as diffraction inspection) Such inspection is referred to as specular reflection inspection), and inspection using a change in polarization state due to structural birefringence of a pattern (hereinafter, such inspection is referred to as PER inspection). According to these inspection methods, it is possible to detect a line width defect, a resist coating defect, and the like based on defocus and dose shift of the exposure apparatus at high speed and with high accuracy.

In such a surface inspection device, in order to control the amount of illumination light irradiated to the substrate, for example, at the exit end of the light amount detection fiber branched from the guide fiber guided from the light source to the illumination optical system that illuminates the substrate, A light amount sensor for detecting the amount of illumination light is provided.
JP 2002-162368 A

  However, if the light quantity sensor provided in the light quantity detection fiber is used, distortion, fine scratches, and dust adhere to the optical system provided between the exit end of the guide fiber that guides light from the light source and the detection unit. When such a problem occurs, an error occurs between the amount of illumination light detected by the sensor and the amount of illumination light that is actually irradiated onto the substrate, resulting in a problem that accuracy in substrate inspection is reduced.

  Further, when a sensor is provided at a position for receiving illumination light on the holder, when the test substrate is large, for example, when the effective diameter is about 300 mm, the central portion of the effective diameter and the effective diameter outer edge of the holder provided with the sensor There is a big difference in the amount of light that reaches the vicinity, but with the recent increase in the number of pixels of image sensors such as CCDs used for surface inspection, it is difficult to increase the dynamic range, and there is an error in the detected illumination light amount. There was a problem that it was likely to occur.

  The present invention has been made in view of such problems, and can detect the amount of illumination light that irradiates a substrate with high accuracy to improve the inspection accuracy of the surface of the substrate and the illumination. It is an object of the present invention to provide a light amount control method.

  In order to achieve such an object, a surface inspection apparatus according to the present invention includes a holder for mounting and holding a test substrate, and an illumination unit that irradiates illumination light onto the surface of the test substrate mounted and held by the holder. A first detection unit that detects light from the surface of the test substrate irradiated with the illumination light, and a defect detected on the surface of the test substrate based on the light detected by the first detection unit. In a surface inspection apparatus having an inspection unit for inspecting presence / absence, a light amount of regular reflection light from a reflection unit provided at a position of the holder that receives the illumination light and the reflection unit irradiated with the illumination light is detected. And a control unit that controls the amount of illumination light based on the amount of light detected by the second detection unit.

  In addition, it is preferable that the said 2nd detection part is provided in the optical path from the said illumination part to the said 1st detection part in front of the said 1st detection part so that insertion / extraction is possible.

  Moreover, it is preferable that the said reflection part is mirror-finished.

  Moreover, it is preferable that the said holder has a ditch | groove opened on the board | substrate contact surface which contacts the said test substrate, and the said reflection part is provided in the bottom part of the said ditch | groove of the said board | substrate contact surface.

  Moreover, it is preferable that the holder can be tilted to change the mounting angle of the test substrate.

  The holder is preferably made of ceramics.

  Further, the light amount control method for illumination light according to the present invention uses the surface inspection apparatus described above, and immediately before the surface inspection of the substrate to be detected by the inspection unit, the second detection unit causes the reflection unit to The amount of specularly reflected light is detected, and the amount of illumination light is controlled based on the amount of light detected by the second detector by the controller.

  In addition, the method for controlling the amount of illumination light according to the present invention uses the above-described surface inspection apparatus, and each time a predetermined number of surface inspections of the substrate to be inspected by the inspection unit are completed, the second detection unit performs the reflection unit. The amount of the regular reflection light from the light is detected, and the amount of illumination light is controlled based on the amount of light detected by the second detection unit by the control unit.

  ADVANTAGE OF THE INVENTION According to this invention, the light quantity of the illumination light which irradiates a board | substrate can be detected with high precision, and the surface inspection apparatus and the light quantity control method of illumination light which can improve the test | inspection precision of a board | substrate surface can be provided. .

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the surface inspection apparatus 1 according to the present embodiment includes a holder 20 that supports a semiconductor wafer 10 (hereinafter referred to as a wafer 10) that is a substrate to be tested, an illumination optical system 30, and an imaging optical system 40. The image processing device 50 and the control device 55 are mainly configured. The surface inspection apparatus 1 is an apparatus that automatically inspects the surface of a wafer 10 in a manufacturing process of a semiconductor circuit element. After exposure / development of the uppermost resist film, the wafer 10 is carried from a wafer cassette (not shown) or a developing device by a conveyance system (not shown) and is sucked and held by the holder 20.

  As shown in FIG. 2, a plurality of chip regions 11 are arranged in the XY direction on the surface of the wafer 10, and a predetermined repetitive pattern 12 is formed in each chip region. As shown in FIG. 3, the repetitive pattern 12 is a resist pattern (for example, a wiring pattern) in which a plurality of line portions 2A are arranged at a constant pitch P along the short direction (X direction). Between adjacent line parts 2A is a space part 2B. The arrangement direction (X direction) of the line portions 2A is referred to as “repeating direction of the repeating pattern 12”.

Here, the design value of the line width D _A of the line portion 2A in the repetitive pattern 12 and 1/2 of the pitch P. That is, the repetitive pattern 12 has a concavo-convex shape in which the line portions 2A and the space portions 2B are alternately arranged along the X direction. line width D _B of the line width D _a and the space portion 2B of 2A are equal, the volume ratio of the line portion 2A and the space portion 2B is substantially 1: 1. In the case of such an ideal shape, the light amount (light intensity) of the polarization component detected by the imaging optical system 40 described later is the largest. In contrast, when the exposure focus deviates from an appropriate value, the pitch P does not change, with the line width D _A of the line portion 2A becomes different from a design value, becomes different even with the line width D _B of the space portion 2B, The volume ratio between the line portion 2A and the space portion 2B deviates from about 1: 1. At this time, the amount of light of the polarization component is smaller than in the ideal case.

  The surface inspection apparatus 1 of the present embodiment performs defect inspection of the repetitive pattern 12 by using the change in the volume ratio between the line portion 2A and the space portion 2B in the repetitive pattern 12 as described above. As described above, the change in the volume ratio appears for each shot area of the wafer 10 due to the deviation of the exposure focus from the appropriate state.

  In the present embodiment, it is assumed that the pitch P of the repeating pattern 12 is sufficiently small as compared with the wavelength of illumination light (linearly polarized light L described later) with respect to the repeating pattern 12. For this reason, diffracted light is not generated from the repetitive pattern 12, and the defect inspection of the repetitive pattern 12 cannot be performed by diffracted light.

  The holder 20 of the surface inspection apparatus 1 supports the wafer 10 on the upper surface and fixes and holds the wafer 10 by, for example, vacuum suction. Furthermore, the holder 20 is rotatable about the normal A1 at the center of the upper surface of the holder as a central axis. By this rotation mechanism, the repeating direction of the repeating pattern 12 on the wafer 10 (the X direction in FIGS. 2 and 3) can be rotated within the surface of the wafer 10. The holder 20 can be tilted (tilted) about an axis A2 passing through the upper surface of the holder. Thereby, the mounting angle of the wafer 10 can be changed.

  In the present embodiment, in order to maximize the sensitivity of defect inspection of the repeated pattern 12, the repeated direction of the repeated pattern 12 on the wafer 10 is changed to illumination light (linearly polarized light L) on the surface of the wafer 10 as shown in FIG. Inclination is set at an angle of 45 degrees with respect to the vibration direction. The angle is not limited to 45 degrees, and can be set in an arbitrary angle direction such as 22.5 degrees or 67.5 degrees.

  As shown in FIG. 1, the illumination optical system 30 includes an illumination device 31 that emits light having a specific wavelength, a first polarizing plate 32, and a first concave reflecting mirror 33. . The illumination device 31 mainly includes a light source 31a, a wavelength selection unit 31b that selectively transmits light having a specific wavelength, and a light guide fiber 31c that guides light transmitted through the wavelength selection unit 31b. The light source 31a has a built-in discharge light source such as a metal hydride lamp or a mercury lamp, and emits light in a wavelength region of, for example, about 180 nm to 600 nm by power supplied from a power supply unit (not shown). Yes. The power supply unit is electrically connected to a control device 55 described later, and the power supplied to the light source 31a is controlled by a control signal output from the control device 55 (that is, irradiated from the light source 31a). The amount of illumination light is controlled).

  The first polarizing plate 32 is detachably disposed on an optical path between the illumination device 31 and the first concave reflecting mirror 33, and the light emitted from the illumination device 31 is a straight line corresponding to the direction of the transmission axis. The polarized light is L (see FIG. 4). The first concave reflecting mirror 33 is a reflecting mirror whose inner surface is a reflecting surface, the front focal point substantially coincides with the exit end of the light guide fiber 31 c of the illumination device 31, and the rear focal point is the surface of the wafer 10. It arrange | positions diagonally upward of the holder 20 so that it may correspond substantially. Then, the first concave reflecting mirror 33 converts the light from the first polarizing plate 32 reflected by the first concave reflecting mirror 33 into a parallel light beam and irradiates the wafer 10 that is the test substrate.

  That is, the illumination optical system 30 is an optical system telecentric with respect to the wafer 10 side. The optical axis O1 of the illumination optical system 30 on the wafer 10 side with respect to the first concave reflecting mirror 33 is tilted by an angle θi with respect to the normal A1 of the holder 20, and is orthogonal to the tilt axis A2 of the holder 20. ing.

  In the illumination optical system 30, the light from the illumination device 31 becomes p-polarized linearly polarized light L via the first polarizing plate 32 and the first concave reflecting mirror 33, and is applied to the entire surface of the wafer 10 as illumination light. Incident. At this time, since the traveling direction of the linearly polarized light L (the direction of the principal ray of the linearly polarized light L reaching an arbitrary point on the surface of the wafer 10) is substantially parallel to the optical axis O1, the linearly polarized light at each point on the wafer 10 The incident angles of L are the same because of the parallel light flux, and correspond to an angle θi formed by the optical axis O1 and the normal line A1.

  In this embodiment, since the linearly polarized light L incident on the wafer 10 is p-polarized light, the repeating direction of the repeated pattern 12 is the incident surface of the linearly polarized light L (linearly polarized light on the surface of the wafer 10) as shown in FIG. When the angle is set to 45 degrees with respect to the L traveling direction), the angle formed by the vibration direction of the linearly polarized light L on the surface of the wafer 10 and the repeating direction of the repeating pattern 12 is also set to 45 degrees. In other words, the linearly polarized light L changes into the repeated pattern 12 so as to cross the repeated pattern 12 diagonally with the vibration direction of the linearly polarized light L on the surface of the wafer 10 inclined by 45 degrees with respect to the repeated direction of the repeated pattern 12. It will be incident.

  As shown in FIG. 1, the imaging optical system 40 includes a second concave reflecting mirror 41, a second polarizing plate 42, an aperture stop 43, an imaging lens 44, and an imaging device 45. The optical axis O2 is disposed so as to be inclined by the same angle θr as the angle θi with respect to the normal A1 passing through the center of the holder 20. Therefore, the specularly reflected light that is specularly reflected on the surface of the wafer 10 (repeated pattern 12) travels along the optical axis O2 of the imaging optical system 40. The second concave reflecting mirror 41 is a reflecting mirror similar to the first concave reflecting mirror 33, and the specularly reflected light from the wafer 10 is reflected by the second concave reflecting mirror 41 and condensed, and the second The polarizing plate 42, the aperture stop 43, the imaging lens 44, and the imaging lens of the imaging device 45 reach the imaging surface of the imaging device 45 to form an image of the wafer 10.

  The second polarizing plate 42 is detachably disposed on the optical path between the second concave reflecting mirror 41 and the aperture stop 43, and the direction of the transmission axis of the second polarizing plate 42 is the illumination optics described above. It is set to be orthogonal to the transmission axis of the first polarizing plate 32 of the system 30 (crossed Nicol state). Accordingly, the second polarizing plate 42 extracts the polarized light component (for example, the s-polarized light component) whose vibration direction is substantially perpendicular to the linearly polarized light L from the regular reflected light from the wafer 10 (repeated pattern 12). It can be led to the device 45. As a result, a reflected image of the wafer 10 is formed on the imaging surface of the imaging device 45 by a polarized light component whose vibration direction is substantially perpendicular to the linearly polarized light L of the regular reflected light from the wafer 10.

  The imaging device 45 is composed of, for example, a CCD imaging device or the like, photoelectrically converts a reflected image of the wafer 10 formed on the imaging surface, and outputs an image signal to the image processing device 50. The brightness and darkness of the reflected image of the wafer 10 is approximately proportional to the light amount (light intensity) of the polarization component detected by the imaging device 45 and changes according to the shape of the repeated pattern 12. The reflected image of the wafer 10 is brightest when the repeated pattern 12 has an ideal shape. The brightness of the reflected image of the wafer 10 appears for each shot area.

  The image processing device 50 captures a reflected image of the wafer 10 based on the image signal output from the imaging device 45. Note that the image processing apparatus 50 stores a reflection image of a non-defective wafer in advance for comparison. A non-defective wafer is one in which the repetitive pattern 12 is formed on the entire surface in an ideal shape. Therefore, it is considered that the luminance information (signal intensity) of the reflected image of the non-defective wafer indicates the highest luminance value.

  Therefore, when the image processing apparatus 50 captures the reflection image of the wafer 10 as the test substrate, the image processing apparatus 50 compares the luminance information (signal intensity) with the luminance information (signal intensity) of the reflection image of the non-defective wafer. Then, the defect of the repetitive pattern 12 is detected based on the amount of decrease in the luminance value of the dark portion in the reflected image of the wafer 10. For example, if the light amount change is larger than a predetermined threshold (allowable value), it is determined as “defect”, and if it is smaller than the threshold, it is determined as “normal”. Then, the comparison result of the luminance information (signal intensity) by the image processing device 50 and the reflected image of the wafer 10 at that time are output and displayed on a monitor (not shown).

  In the image processing apparatus 50, as described above, in addition to the configuration in which the reflection image of the non-defective wafer is stored in the image storage unit 51 in advance, the array data of the shot area of the wafer 10 and the threshold value of the brightness value are stored in advance. It is also possible to use a configuration. In this case, since the position of each shot area in the reflected image of the captured wafer 10 is known based on the array data of the shot area, the luminance value of each shot area is obtained. Then, a pattern defect is detected by comparing the brightness value with a stored threshold value. A shot area having a luminance value smaller than the threshold value may be determined as a “defect”.

  The control device 55 comprehensively controls operations of the holder 20, the lighting device 31, and the like. The control device 55 is electrically connected to an information input device 56 for an operator to perform an input operation.

  Furthermore, as shown in FIG. 5, the surface inspection apparatus 1 detects the light quantity of the regular reflection light from the reflection part 61 provided in the position which receives the illumination light of the holder 20, and the reflection part 61 irradiated with the illumination light. The light amount detector 62 outputs a detection signal to the controller 55, and the controller 55 checks and controls (monitors) the amount of illumination light emitted from the light source 31a. (In practice, the power supplied to the light source 31a from a power supply unit (not shown) is controlled).

  With this configuration, the amount of illumination light that irradiates the wafer 10 can be detected with high accuracy. Therefore, the wafer 10 can always be irradiated with a predetermined amount of light, and the inspection accuracy of the surface of the wafer 10 can be improved. Can do.

  In addition, it is preferable that the light quantity detection part 62 is provided in the optical path from the illumination optical system 30 to the imaging optical system 40 in the front of the imaging device 45 so that insertion / extraction is possible. With this configuration, the light amount detection unit 62 can detect almost all of the light received by the imaging device 45 while being hardly affected by disturbance such as uneven illumination. As a result, the accuracy of detecting the amount of illumination light is increased, which leads to improvement in the accuracy of surface inspection of the wafer 10.

  Moreover, it is preferable that the reflection part 61 is mirror-finished. With this configuration, it is possible to reduce light scattering in the reflection unit 61 and improve the light intensity guided to the light amount detection unit 62. That is, since the intensity of the light incident on the light amount detection unit 62 can be increased, a minute change can be detected, and the light amount detection accuracy can be improved.

  Moreover, the reflection part 61 can also be provided in the ditch | groove 20b opened to the board | substrate contact surface 20a which contacts the wafer 10 currently formed in the holder 20, as shown in FIG. With this configuration, since the reflecting portion 61 can be provided at substantially the same position as the contact surface 20a of the wafer 10, it is possible to detect the same amount of light as the illumination light actually irradiated on the wafer 10.

  The holder 20 is preferably made of ceramics, which is a lightweight and highly rigid material. Ceramics is a high-hardness material and has excellent wear resistance, can hold the wafer 10 while maintaining the planar accuracy of the wafer 10, and further repeatedly loads and unloads the wafer 10 with respect to the holder 20. Even if it is difficult to wear. Further, since the area of the substrate contact surface 20a of the holder 20 can be reduced (that is, the supporting portion of the wafer 10 is made thinner), the area of the concave groove bottom portion 20b provided with the (mirror-finished) reflecting portion 61 is increased. As a result, the illumination light quantity detection accuracy can be increased.

  Here, an example of the illumination light quantity detection process in the surface inspection apparatus 1 will be described with reference to the flowchart of FIG. First, the holder 20 is tilted so as to satisfy the regular reflection condition (in a state where the wafer 10 is not placed) (step S1). Next, the light amount detection unit 62 is inserted at a predetermined position immediately before the imaging device 45 on the optical path from the illumination optical system 30 to the imaging optical system 40 (step S2). Then, electric power is supplied to the light source 31a by the control apparatus 55, and illumination light is irradiated toward the holder 20 (step S3). And the light quantity of the illumination light irradiated to the reflection part 61 on the holder 20 is detected by the light quantity detection part 62 (step S4). The light amount detection unit 62 then transmits a detection signal to the control device 55. Then, the control apparatus 55 controls the electric power to the light source 31a based on the received detection signal, and controls the illumination light quantity (step S5). Then, the light amount detection unit 62 is retracted from the optical path (step S6), and the holder 20 is tilted back to the mounting angle of the wafer 10 so as to be suitable for the surface inspection (step S7), and this process is terminated. Thereafter, the inspection wafer 10 is placed on the upper surface of the holder 20, and the defect inspection for the repetitive pattern 12 on the surface of the wafer 10 is started. After the predetermined number of sheets is completed, the process returns to step S1.

  Note that it is preferable to periodically check the amount of illumination light as described above immediately before the start of the surface inspection of the wafer 10 or every time a predetermined number of surface inspections (for example, cassette units) are completed. This is because it is possible to perform wafer surface inspection with high accuracy by detecting the amount of illumination light by the light amount detector 62 and controlling the amount of illumination light immediately before the surface inspection of the wafer 10. It is.

  In the above-described embodiment, the reflection unit 61 is provided on the surface of the holder 20 on which the wafer 10 is placed, but is not limited thereto. For example, as shown in FIG. 7, the back surface of the holder 20 may be mirror-finished and used as the reflecting portion 61. In this case, the holder 20 is rotated immediately before the wafer 10 is placed on the holder 20, and then the holder 20 is tilted so that the reflection part 61 on the back surface of the holder 20 satisfies the regular reflection condition. It is possible to detect the amount of illumination light.

  In the above-described embodiment, the amount of illumination light is controlled by controlling the power supplied from the power supply unit (not shown) to the light source 31a, but may be performed using a neutral density filter, for example. Good.

  In the above-described embodiment, the illumination optical system 30 irradiates the surface of the wafer 10 with the linearly polarized light L as the illumination light, and the imaging optical system 40 has substantially the same direction as the linearly polarized light L of the regular reflected light from the wafer 10 and the vibration direction. Although an image of the wafer 10 is picked up with a right-angle polarization component, the present invention is not limited to this. For example, with the first and second polarizing plates 32 and 42 removed from the optical path, the illumination optical system 30 irradiates the surface of the wafer 10 with illumination light (not polarized), and the imaging optical system 40 You may make it image the image of the wafer 10 by the diffracted light emitted from the surface. As described above, the illumination light applied to the surface of the wafer 10 is not limited to linearly polarized light, but can be applied to elliptically polarized light other than linearly polarized light or normal illumination light.

It is a figure showing the whole surface inspection device composition concerning the present invention. It is an external view of the surface of a semiconductor wafer. It is a perspective view explaining the uneven structure of a repeating pattern. It is a figure explaining the inclination state of the entrance plane of a linearly polarized light and the repeating direction of a repeating pattern. It is a figure which shows the structure of the holder which concerns on this invention. It is a flowchart explaining the detection process of illumination light quantity. It is a figure which shows another structure of the holder which concerns on this invention.

Explanation of symbols

1 Surface inspection device 10 Wafer (Subject to be tested)
20 Holder 20b Concave groove 30 Illumination optical system (illumination unit)
31 Illumination device 31a Light source 40 Imaging optical system (detection unit)
50 Image processing device
55 Control Device 61 Reflector 62 Light Amount Detector

Claims (8)

A holder for placing and holding the test substrate;
An illumination unit that irradiates illumination light onto the surface of the test substrate placed and held by the holder;
A first detection unit for detecting light from the surface of the substrate to be tested that has been irradiated with the illumination light;
In the surface inspection apparatus having an inspection unit that inspects the presence or absence of defects on the surface of the substrate to be tested based on the light detected by the first detection unit.
A reflection portion provided at a position of the holder for receiving the illumination light;
A second detector that detects the amount of specularly reflected light from the reflector irradiated with the illumination light;
A surface inspection apparatus comprising: a control unit that performs light amount control of the illumination light based on the light amount detected by the second detection unit.   The surface inspection according to claim 1, wherein the second detection unit is provided so as to be insertable / removable immediately before the first detection unit on an optical path from the illumination unit to the first detection unit. apparatus.   The surface inspection apparatus according to claim 1, wherein the reflection portion is mirror-finished. The holder has a concave groove that opens in a substrate contact surface that comes into contact with the test substrate;
The surface inspection apparatus according to claim 1, wherein the reflection portion is provided at a bottom portion of the concave groove of the substrate contact surface.   The surface inspection apparatus according to claim 1, wherein the holder is tilted to change a mounting angle of the test substrate.   The surface inspection apparatus according to claim 1, wherein the holder is made of ceramics. Using the surface inspection apparatus according to claim 1,
Immediately before the start of the surface inspection of the test substrate by the inspection unit,
The second detection unit detects the amount of the regular reflection light from the reflection unit,
A method of controlling the amount of illumination light, wherein the amount of illumination light is controlled based on the amount of light detected by the second detection unit by the control unit. Using the surface inspection apparatus according to claim 1,
Every time a predetermined number of surface inspections of the test substrate by the inspection unit are completed,
The second detection unit detects the amount of the regular reflection light from the reflection unit,
A method of controlling the amount of illumination light, wherein the amount of illumination light is controlled based on the amount of light detected by the second detection unit by the control unit.

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