TWI468674B - Method for inspection of multi - crystalline wafers - Google Patents

Description

Multi-crystal wafer inspection method

The present invention relates to a method of inspecting a defect in a polycrystalline wafer such as a polycrystalline germanium wafer for a solar cell by transmitting infrared rays.

In the method disclosed in Patent Document 1, infrared rays are irradiated onto a germanium wafer, and a transmitted infrared light is photographed by a CCD camera, and defects such as micro cracks are detected by image processing from the photographed image at this time.

Further, in the method disclosed in Patent Document 2, infrared rays are irradiated from the front and back surfaces of the polycrystalline wafer, and infrared reflected light from the surface and infrared transmitted light from the back surface are photographed by an infrared camera, and images from the front and back are used. The comparison result of the data detects the crack defect inside the polycrystalline wafer.

However, in the case where the object to be detected is a polycrystalline germanium wafer, when a general infrared light transmitting technique is used, a crystal pattern covering a crystal direction, a crystal boundary or a contour thereof is taken as an image, and thus image processing is performed. In the process, the identification of crystal patterns and defects will be difficult, and it is prone to false detection or neglect of defects.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2007-258555

Patent Document 2: Japanese Patent Laid-Open Publication No. 2007-218638

SUMMARY OF THE INVENTION It is an object of the present invention to reliably detect defects in a polycrystalline wafer by thinning a crystal pattern covering a crystal orientation, a crystal boundary or a contour thereof of a polycrystalline wafer during photographing.

According to the above-described problem, the inventors of the present invention repeated the experiment by irradiating infrared rays to a polycrystalline wafer and observing the transmission of infrared rays. The result is the following insights. That is, when the infrared rays transmitted through the polycrystalline wafer are directly observed at the irradiation position of the infrared ray, the crystal pattern of the polycrystalline wafer of the photographic image cannot be lightened. However, when the irradiation position of the infrared ray and the observation position of the transmitted infrared ray, that is, the imaging position of the camera are separated by an appropriate distance, the crystal pattern of the polycrystalline wafer can be made light and can be made only in the polycrystalline wafer. The brightness of the defect is different from the brightness of other normal parts. The present invention has been completed on the basis of such findings.

In order to achieve the above object, the present invention discloses the following.

(1) A method for inspecting a polycrystalline wafer, comprising: a step of irradiating infrared rays toward the irradiation position from a light source disposed at an irradiation position on a polycrystalline wafer from an optical axis; and injecting infrared rays from the irradiation position Repeating the refraction and reflection inside the polycrystalline wafer, and ejecting the photographing position from the photographing position on the polycrystalline wafer at a predetermined distance from the irradiation position toward the surface of the polycrystalline wafer a step of photographing the camera; and detecting a defect in the polycrystalline wafer based on a difference in brightness between the defect-free portion and the defective portion on the photographic image obtained by the camera.

(2) The method for inspecting a polycrystalline wafer according to (1), wherein the photographing position is set to a surface opposite to the surface of the polycrystalline wafer on which the irradiation position is set.

(3) The method for inspecting a polycrystalline wafer according to (1), wherein the photographing position is set to be the same surface of the polycrystalline wafer surface on which the irradiation position is set.

(4) The method for inspecting a polycrystalline wafer according to any one of (1) to (3) wherein the light source is a single light source, and an optical axis of the light source is inclined to a surface of the polycrystalline wafer And it is possible to extend from the above-described irradiation position to the above-described photographing position side.

(5) The method for inspecting a polycrystalline wafer according to any one of (1) to (3) wherein the light source is a plurality of light sources arranged substantially symmetrically with respect to the photographing position, and the optical axis of each of the light sources The surface of the polycrystalline wafer is inclined at the same inclination angle, and is extendable from the respective irradiation positions to the photographing position side.

(6) The method for inspecting a polycrystalline wafer according to any one of (1) to (5) wherein the light source is a linear light source, the camera is a line sensor type camera, and the camera is used for detecting Infrared light concentrated by a cylindrical lens.

(7) The method for inspecting a polycrystalline wafer according to any one of (1) to (5) wherein the light source is a ring-shaped light source forming a ring-shaped irradiation region, and the camera is a ring-shaped irradiation region. The inner side is a zone sensor type camera of the photographing area, and the above-mentioned camera is for detecting the above-mentioned infrared rays condensed by the magnifying lens.

According to the inspection method of the polycrystalline wafer of the present invention, the infrared rays incident on the polycrystalline wafer from the irradiation position are repeatedly reflected or refracted in the polycrystalline wafer, and are separated from the irradiation position in the direction of the surface of the polycrystalline wafer. The photographic position on the later crystalline wafer is emitted. By photographing the infrared ray emitted from the photographing position by the camera, it is possible to obtain a photographic image in which the crystal pattern is lightened and the defect is clearly recognized, and the defect can be easily and surely detected.

Specifically, when there is no defect in the polycrystalline wafer, since the infrared rays are repeatedly reflected or refracted in the polycrystalline wafer, the intensity of the infrared rays reaching the photographing position is substantially uniform, and is hardly affected by the crystal pattern. Therefore, the photographic image obtained by the camera will become a uniform luminance image that does not reflect the crystal pattern of the polycrystalline wafer.

However, when there is a defect in the polycrystalline wafer, the defect causes the infrared rays to be reflected indiscriminately, and the intensity of the infrared rays reaching the photographing position becomes non-uniform. Therefore, on the photographic image obtained by the camera, the defect will appear as a region having a lower brightness than in the case where there is no defect. Thus, according to the present invention, the photographic image obtained by the camera is substantially unaffected by the crystal pattern covering the crystal orientation, the crystal boundary or the outline of the polycrystalline wafer, since only the luminance of the defect and the non-defective portion is different, Defective detection of defects in polycrystalline wafers.

1 and 2 show an optical system for carrying out the inspection method of the polycrystalline wafer 1 of the present invention. 1 is a side view showing an optical system in a state in which the inspection direction (transport direction of the polycrystalline wafer 1) A is from right to left, and FIG. 2 is a front view showing an optical system in which the inspection direction A is in a state from the paper surface toward the paper surface.

An optical system for carrying out the inspection method of the polycrystalline wafer 1 of the present invention will be described with reference to Figs. 1 and 2 .

First, a line extending in a direction orthogonal to the conveyance direction A of the polycrystalline wafer 1 is irradiated from the linear light source 2 disposed on the lower surface side of the polycrystalline wafer 1 toward the linear irradiation position P1 of the polycrystalline wafer 1. Infrared infrared 3. At this time, the light source 2 is disposed such that the optical axis of the light source 2 passing through the irradiation position P1 is inclined with respect to the normal line n1 of the surface of the polycrystalline wafer 1. Specifically, the optical axis of the light source 2 forms an inclination angle α with respect to the normal line n1 so that the infrared ray 3 emitted from the light source 2 extends from the irradiation position P1 side to the imaging position P2 side.

Such a linear light source 2 can be configured by linearly arranging a plurality of infrared light-emitting diodes or by combining a rod-shaped infrared light source and a light source cover forming a linear slit.

As schematically shown in FIG. 3, the infrared rays 3 incident from the irradiation position P1 are repeatedly reflected and refracted inside the polycrystalline wafer 1, and are repeatedly reflected on the front and back surfaces of the polycrystalline wafer 1 to reach the photographing position. P2. A part of the infrared ray 3 reaching the photographing position P2 is reflected, and a part is directly emitted from the surface of the polycrystalline wafer 1. Among them, the infrared rays 3 emitted from the photographing position P2 are arranged by the camera 6 of the photographing position P2 by the optical axis 7, and the photographed image is obtained by the camera 6. Here, the photographing position P2 is set at a position separated from the irradiation position P1 by a predetermined distance D in the plane direction of the polycrystalline wafer 1.

In the present embodiment, the camera 6 is disposed on the opposite side of the light source 2 with respect to the polycrystalline wafer 1. Further, the optical axis 7 of the camera 6 passes through the photographing position P2 and is perpendicular to the surface of the polycrystalline wafer 1.

The wavelength of the infrared ray 3 which is linearly irradiated is preferably a wavelength suitable for detecting an internal defect, for example, a wavelength region of 0.7 μm to 2.5 μm. In addition, the camera 6 preferably also has good sensitivity in this wavelength region.

The photographing position P2 is set at a position away from the irradiation position P1 by a predetermined distance D. The distance D can be set in accordance with the crystal structure of the polycrystalline wafer 1 or its thickness, and can be set at an optimum position where the crystal pattern becomes light.

Further, the inspection method of the present invention is preferably applied to a polycrystalline wafer 1 having a thickness of 0.1 to 0.25 mm. The reason for this is that the thicker the thickness of the polycrystalline wafer 1, the more the infrared ray 3 is refracted and reflected inside the polycrystalline wafer 1, and the intensity of the infrared ray 3 captured by the camera 6 is lowered, and a remarkable photographic image cannot be obtained. . When the thickness of the polycrystalline wafer 1 is reduced, the number of times of refraction or reflection occurring when the infrared ray 3 reaches the photographing position P2 is reduced, and the photographic image obtained by the camera 6 remains in a crystal pattern.

Further, it is preferable that the optical axis of the light source 2 is set to a range of 20° or more and 40° or less with respect to the inclination angle α of the normal line n1 on the surface of the polycrystalline wafer 1. The reason for this is that when the tilt angle α is less than 20°, the number of times of the refraction ‧ reflection required for the infrared ray 3 to reach the photographing position P2 after leaving the predetermined distance D from the irradiation position P1 becomes large, and the infrared ray photographed by the camera 6 is made. 3 The intensity is lowered and no obvious photographic image can be obtained. When the inclination angle α is larger than 20°, the number of times of refraction ‧ reflection required for the infrared ray 3 to reach the photographing position P2 is reduced, and the photographic image may remain in the crystal pattern.

Further, the predetermined distance D between the irradiation position P1 and the photographing position P2 is preferably set to 1 to 3 mm. When the predetermined distance D is shorter than 1 mm, the number of times of refraction ‧ reflection required for the infrared ray 3 to reach the photographing position P2 will be small, and the photographic image will remain crystallized. When the predetermined distance D is longer than 3 mm, the number of refractions ‧ reflections will become larger, and the intensity of the infrared ray 3 photographed by the camera 6 will decrease, and a clear photographic image cannot be obtained.

In the inspection method of the polycrystalline wafer 1 of the present invention, in order to make the influence of the crystal pattern small and to obtain a visible photographic image, the thickness and the inclination angle α of the polycrystalline wafer 1 are appropriately set within the above range. , the established distance D.

In the optical system for performing the inspection method of the polycrystalline wafer 1 configured as described above, the infrared ray 3 passing through the defect-free region of the polycrystalline wafer 1 without defects is in the crystal direction of a plurality of randomly existing crystal grains. Or the boundary of the crystal is repeatedly refracted or reflected to reach the photographing position P2. Repeating the plurality of random refracted or reflected infrared rays 3, the refraction of each crystal grain at the photographing position P2 after reaching the predetermined distance D from the irradiation position P1, the influence of the reflections will cancel each other, so that the camera 6 is photographed at the photographing position P2. The photographic image there will become a linear photographic image with uniform brightness.

On the other hand, when the polycrystalline wafer 1 has the defect 4, the infrared ray 3 will be randomly reflected or absorbed in the defect 4, and thus the photographic image photographed at the photographing position P2 may appear due to the above. The shadow or bright part caused by defect 4. Since the shadow or the bright portion caused by the defect 4 has a different brightness from the photographic image formed by the infrared ray 3 passing through the defect-free region, the defect 4 can be detected by comparing the brightness of both.

The multi-crystal wafer 1 is conveyed in the conveyance direction A, and the above steps are continuously repeated to obtain a photographic image having an area as shown in FIGS. 4A and 4B.

4A and 4B show a photographic image of the camera 6 that images the infrared ray 3 that has passed through the region containing the defect 4.

In Fig. 4A, a bright image in which a darker shadow is generated by the infrared rays 3 passing through the defect 4 is formed in a background image in which the uniform brightness of the infrared rays 3 passing through the defect-free region is formed. Therefore, the defect 4 can be easily and surely recognized by detecting a region having a different luminance from the background image of the uniform luminance. In addition, FIG. 4A is a photographic image obtained by setting a polycrystalline wafer 1 having a thickness of 0.2 mm as a defect detection target under a set condition of a predetermined distance D=2 mm and an inclination angle α=20°.

Further, in the present invention, the photographing position P2 is set at a position separated from the irradiation position P1 by a predetermined distance D = 2 mm in the plane direction of the polycrystalline wafer 1. On the other hand, when the photographing position is set at the position P3 where the predetermined distance D of the optical axis extension line of the light source 2 is shorter than 1 mm (refer to FIG. 1), it can be photographed at the photographing position P3 and is not sufficiently repeated. The infrared rays 3 emitted by refraction or reflection, so the photographic image will be an image affected by the crystal boundary. Therefore, even if a photographic image is formed from the infrared ray 3 passing through the region containing the defect 4, as shown in Fig. 4B, the portion affected by the defect 4 is buried in the crystal pattern, making the recognition of the defect 4 and the crystal pattern difficult. .

5 is a position where the two linear light sources 2 are arranged on the line on the lower side of the polycrystalline wafer 1 with respect to the normal line at the photographing position P2 (the optical axis 7 of the camera 6), and are directed from the respective light sources 2 toward the polycrystalline crystal. The irradiation position P1 at two positions in the circle 1 illuminates the linear infrared rays 3 in different oblique directions. Further, in this example, the inclination angle formed by the optical axis of each light source 2 and the surface of the polycrystalline wafer 1 is set to be substantially the same. According to this example, in addition to the above effects, since the amount of light of the infrared ray 3 detectable by the camera 6 is increased, a bright photographic image can be obtained, so that the defect 4 can be easily detected.

Further, Fig. 6 uses a cylindrical lens 8 to condense the infrared rays 3 that have passed through the polycrystalline wafer 1, and detects the condensed infrared rays 3 by the line sensor type camera 6. In this example, the cylindrical lens 8 is arranged such that the longitudinal direction thereof is along the linear infrared rays 3, and the imaging of the infrared rays 3 is enlarged in the conveyance direction of the polycrystalline wafer 1.

As described above, when the infrared ray 3 is amplified by the lens 8, the infrared ray 3 can be easily detected by the camera 6, and the erroneous detection or ignoring of the continuous movement of the polycrystalline wafer 1 can be reduced, which is advantageous. In other words, the lens 8 can also be incorporated into the single light source 2 as shown in FIGS. 1 and 2.

Further, the specific size or the arrangement of the optical system or the like can be set to an appropriate value in accordance with the thickness of the polycrystalline wafer 1, the wavelength region of the infrared ray 3, the irradiation angle of the infrared ray 3, the sensitivity of the camera 6, and the like.

Next, in Fig. 7, the light source 2 is a ring type light source, the camera 6 is a regional type camera, and the light source 2 and the camera 6 are disposed on the side opposite to the polycrystalline wafer 1. The ring type light source 2 is concentrically arranged with respect to the optical axis 7 of the camera 6. The irradiation position P1 of the light source 2 is set at a position where the light beam of the infrared ray 3 irradiated by the light source 2 is the largest, which is a circle slightly smaller than the circular shape of the light source 2.

According to the present example, the photographing position (photographing area) P2 is the detection range of the area type camera 6, which is offset from the irradiation position P1 toward the optical axis 7 of the camera 6 by the distance D inside the ring type light source 2 as shown in FIG. The inner side of the circle with a smaller radius. Further, a magnifying convex lens on the objective lens side of the camera 6 may be disposed as needed. Further, the irradiation position P1 may be formed by a slit of a ring type.

According to the example of Fig. 7, the infrared rays 3 from the light source 2 enter the inside of the polycrystalline wafer 1 from the circular irradiation position P1, and after being repeatedly refracted and reflected, reach the inside of the circular photographing position P2 of the camera 6, and the area is The type of camera 6 performs photography.

Since the ring type light source 2 irradiates the infrared ray 3 from the entire direction of the camera 6 toward the irradiation position P1 of the polycrystalline wafer 1, even if the defect 4 in the polycrystalline wafer 1 is not easily detected from a certain direction, the defect can be 4 to test. Further, by using the area type camera 6, the inspection range (observation range) of the polycrystalline wafer 1 can be set to be larger than the linear inspection range, so that the inspection efficiency can be improved.

In addition, FIG. 9 is an example in which the ring type light source 2 and the area type camera 6 are disposed on the same surface side of the polycrystalline wafer 1. In this example, the infrared rays 3 from the light source 2 also enter the inside of the polycrystalline wafer 1 from the circular irradiation position P1, and after repeated refraction and reflection, reach the inside of the circular photographing position P2, and the regional type camera 6 to take photography.

Further, when the infrared ray 3 is reflected on the surface of the polycrystalline wafer 1 and the photographic image is not noticeable, the hood 9 for shielding light can be provided in the camera 6 to prevent the reflected light of the infrared ray 3 from directly entering the camera 6. Further, in this example, the slit position of the ring shape may be used to form the irradiation position P1.

According to the example of FIG. 9, the irradiation position P1 and the photographing position P2 are on the same plane for the polycrystalline wafer 1, and therefore, the portion of the defect 4 in the polycrystalline wafer 1 has a reflection characteristic stronger against the infrared rays 3 than the other normal portions. At this time, the defect 4 can be detected efficiently and easily. Further, even when the irradiation position P1 or the photographing position P2 cannot be set in the state of one surface of the polycrystalline wafer 1, the defect 4 can be detected.

Of course, in the above-described FIGS. 1, 2, 5, and 6 examples, the linear light source 2 may be disposed on the same side of the multi-crystal wafer 1 as the camera 6.

Further, the infrared ray 3 from the linear light source 2 may be a light guide body such as an optical fiber or an acrylic resin plate as shown in the ninth chain line of FIG. 9, and four end faces (four sides) of the polycrystalline wafer 1 may be used. At least one of the end faces is irradiated toward the inside of the polycrystalline wafer 1.

In this case, according to FIGS. 5, 6, 7, and 9, in the movement of the polycrystalline wafer 1, even the front end edge portion of the traveling direction of the polycrystalline wafer 1 or the rear end portion of the traveling direction The edge portion is partially detached from one of the light sources 2 or the light source 2, and if the other light source 2 or other portion of the light source 2 is not detached from the edge portion of the moving polycrystalline wafer 1, the defect 4 can be continuously detected. Therefore, the detection of the defect 4 can also be performed on the edge portion of the polycrystalline wafer 1.

In the above example, the infrared ray 3 is irradiated in the oblique direction toward the irradiation position P1 of the polycrystalline wafer 1. Therefore, in the process in which the infrared ray 3 passes through the polycrystalline wafer 1, the chance of refraction and reflection is more than that in the vertical direction, and the infrared ray 3 is more difficult to be affected by the crystal pattern. However, the irradiation direction of the infrared rays 3 may be set to be substantially perpendicular to the irradiation position P1 of the polycrystalline wafer 1. Even if it is set as such, since the infrared rays 3 are reflected at a plurality of crystal boundaries, the infrared rays 3 are also diffused in directions other than the vertical direction. Therefore, by imaging the diffused infrared rays 3, a photographic image that is not affected by the crystal pattern can be obtained.

In the above example, the infrared ray 3 is irradiated in a state of being inclined toward the irradiation position P1 of the polycrystalline wafer 1 and directed to the imaging position P2. Therefore, since most of the infrared rays 3 pass through the polycrystalline wafer 1 toward the photographing position P2, the necessary amount of light can be secured at the photographing position P2. However, even if the infrared ray 3 passes through the polycrystalline wafer 1 in a direction other than the photographing position P2, the amount of photographic light is generated at the photographing position P2 due to the refraction, reflection, and disorder reflection inside the polycrystalline wafer 1, and therefore, in principle, The inspection of defect 4 can be performed.

When the polycrystalline wafer 1 is stopped at the inspection position, the photographing conditions can be made good. On the other hand, when the shutter speed is prioritized, the polycrystalline wafer 1 can be continuously moved. Further, the posture of the polycrystalline wafer 1 may not be horizontal, and may be set to a vertical or inclined state in accordance with the inspection space.

Further, the present invention is not limited to germanium wafers, and may be used in wafers of other polycrystalline structures.

The present invention has been described in detail above with reference to the specific embodiments thereof, and it is obvious to those skilled in the art that various changes or modifications can be made without departing from the spirit and scope of the invention.

This application is based on the Japanese patent application filed on May 29, 2009 (Japanese Patent Application No. 2009-130725) and the Japanese Patent Application (Japanese Patent Application No. 2009-186304) filed on August 11, 2009. This is for reference.

(industrial availability)

According to the inspection method of the polycrystalline wafer of the present invention, it is possible to obtain a photographic image in which the crystal pattern covering the crystal orientation, the crystal boundary or the outline of the polycrystalline wafer is lightened, and the defect is clearly recognized, and the image can be easily and surely determined. Perform defect detection.

1‧‧‧Multi-crystalline wafer

2‧‧‧Light source

3‧‧‧Infrared

4‧‧‧ Defects

6‧‧‧ camera

7‧‧‧ optical axis

8‧‧‧ lens

9‧‧‧ hood

A‧‧‧ Inspection direction (transport direction of polycrystalline wafer 1)

D‧‧‧established distance

N1‧‧‧ normal

P1‧‧‧ irradiation position

P2‧‧‧Photography location

P3‧‧‧Photography location

‧‧‧‧Tilt angle

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side view of an optical system for carrying out the inspection method of the polycrystalline wafer of the present invention.

Figure 2 is a front elevational view of an optical system for carrying out the inspection method of the polycrystalline wafer of the present invention.

Fig. 3 is an explanatory view showing the state of infrared reflection and refraction inside the polycrystalline wafer.

4A is a photograph of a photographic image of a polycrystalline wafer using infrared rays of the present invention.

4B is a photograph of a photographic image of a polycrystalline wafer using infrared rays in a reference example.

Fig. 5 is a side view of an optical system for carrying out a method of inspecting a polycrystalline wafer according to a variation of the present invention.

Fig. 6 is a side view of an optical system for carrying out a method of inspecting a polycrystalline wafer according to a variation of the present invention.

Fig. 7 is a side view of an optical system for carrying out a method of inspecting a polycrystalline wafer according to a variation of the present invention.

Fig. 8 is a plan view showing an inspection range (observation range) on a polycrystalline wafer.

Fig. 9 is a side view of an optical system for carrying out a method of inspecting a polycrystalline wafer according to a variation of the present invention.

1. . . Polycrystalline wafer

2. . . light source

3. . . infrared

6. . . camera

7. . . Optical axis

A. . . Inspection direction (transport direction of polycrystalline wafer 1)

D. . . Established distance

N1. . . Normal

P1. . . Irradiation position

P2. . . Photography location

P3. . . Photography location

α. . . Tilt angle

Claims (11)

A method for inspecting a polycrystalline wafer, comprising: a step of irradiating infrared rays toward the irradiation position from a light source disposed at an irradiation position on a polycrystalline wafer from an optical axis; and injecting infrared rays from the irradiation position, The crystal grain boundary and the defect in the polycrystalline wafer are repeatedly refracted and reflected, and are emitted from the photographing position on the polycrystalline wafer at a predetermined distance from the irradiation position toward the surface of the polycrystalline wafer. a step of photographing a camera for photographing a position; and a step of detecting a defect in the polycrystalline wafer based on a difference in brightness between the defect-free portion and the defective portion on the photographic image obtained by the camera; the photographing position system The surface on the opposite side of the polycrystalline wafer surface on which the irradiation position is set is set, or the same surface of the polycrystalline wafer surface at the irradiation position is set. The method for inspecting a polycrystalline wafer according to claim 1, wherein the light source is a single light source, and an optical axis of the light source is inclined to a surface of the polycrystalline wafer, and is extendable from the irradiation position to the Photography position side. The method for inspecting a polycrystalline wafer according to the first aspect of the invention, wherein the light source is a plurality of light sources arranged substantially symmetrically with respect to the photographing position, The optical axes of the respective light sources are inclined at the same inclination angle with respect to the surface of the polycrystalline wafer, and are extendable from the respective irradiation positions to the imaging position side. The method for inspecting a polycrystalline wafer according to the first aspect of the invention, wherein the light source is a linear light source, the camera is a line sensor type camera, and the camera is configured to detect infrared rays concentrated by a cylindrical lens. The method for inspecting a polycrystalline wafer according to the first aspect of the invention, wherein the light source is a ring-shaped light source forming a ring-shaped irradiation region, and the camera is an area sensor for making a ring-shaped inner side of the irradiation region a photographing region. In the camera of the type described above, the camera is used to detect the infrared ray collected by the lens for magnification. The method for inspecting a polycrystalline wafer according to claim 2, wherein the light source is a linear light source, the camera is a line sensor type camera, and the camera is used for detecting infrared rays concentrated by a cylindrical lens. The method for inspecting a polycrystalline wafer according to the second aspect of the invention, wherein the light source is a ring-shaped light source forming a ring-shaped irradiation region, and the camera is an area sensor for making a ring-shaped inner side of the irradiation region a photographing region. In the camera of the type described above, the camera is used to detect the infrared ray collected by the lens for magnification. For example, the method for inspecting a multi-crystalline wafer of the third application of the patent scope, wherein The light source is a linear light source, and the camera is a line sensor type camera, and the camera is used for detecting infrared rays concentrated by a cylindrical lens. The method for inspecting a polycrystalline wafer according to claim 3, wherein the light source is a ring-shaped light source forming a ring-shaped irradiation region, and the camera is an area sensor that causes a ring-shaped inner side of the irradiation region to be a photographing region. In the camera of the type described above, the camera is used to detect the infrared ray collected by the lens for magnification. The method for inspecting a polycrystalline wafer according to any one of claims 1 to 9, wherein the predetermined distance is set such that a crystal pattern does not remain in the photographic image, and the identifiable defect can be obtained. The distance from the photographic image. The method for inspecting a polycrystalline wafer according to claim 10, wherein the predetermined distance is set to 1 to 3 mm when the thickness of the polycrystalline wafer is 0.1 to 0.25 mm.