JP4573308B2 - Surface inspection apparatus and method - Google Patents

Description

  The present invention relates to a surface inspection apparatus and method for optically inspecting a plate-like sample surface such as a semiconductor wafer, and more specifically, acquires an image of a sample surface in a state where light is irradiated from the light source device to the surface of the sample. The present invention relates to a surface inspection apparatus and method for detecting defects (scratches, dirt, dust, etc.) on the surface of a sample based on the image.

  2. Description of the Related Art Conventionally, surface inspection apparatuses that detect scratches on the surface of a semiconductor wafer have been proposed (see, for example, Patent Document 1). In this conventional surface inspection apparatus, the surface of a semiconductor wafer irradiated with inspection light from a single light source is imaged by an imaging device under a dark field environment, and the semiconductor wafer is based on an image obtained by the imaging device. Detects scratches on the surface. When the inspection light is irradiated to a fine flaw on the surface of the semiconductor wafer, the inspection light proceeds as light having an intensity distribution biased in a certain direction with respect to the irradiation direction (optical axis direction). When such light enters the imaging device, a bright spot corresponding to a scratch appears in an image obtained by the imaging device. A defect on the surface of the semiconductor wafer can be detected based on the bright spot in the image.

  As described above, when the inspection light is irradiated to the fine scratch on the surface of the semiconductor wafer, the intensity distribution of the light that proceeds from the scratch depends on the irradiation direction (optical axis direction) of the inspection light with respect to the scratch. If the positional relationship between the light source and the imaging device is fixed, some of the scratches on the surface of the semiconductor wafer cannot be detected. Therefore, in the conventional surface inspection apparatus, the semiconductor wafer is held at a predetermined angle (for example, 9 degrees) while maintaining the incident angle of the inspection light with respect to the surface of the semiconductor wafer (the angle formed by the optical axis of the inspection light and the surface of the semiconductor wafer). (Degrees). Then, scratches are detected from the states of bright spots in a plurality of images obtained by the imaging device at a plurality of rotational positions.

JP-A-8-82603

  By the way, the smaller the defects such as scratches on the surface of the semiconductor wafer (for example, crystalline defects), the angle dependence of the intensity distribution of the light proceeding from the scratches when the defects are irradiated with the inspection light with respect to the inspection light. Becomes higher (close to the pure diffraction phenomenon). For this reason, in order to increase the detection accuracy for fine defects in the conventional surface inspection apparatus as described above, the semiconductor wafer image must be acquired at more angular positions by reducing the rotation angle pitch of the semiconductor wafer. I must. If images of the semiconductor wafer are acquired at more angular positions in this way, the number of times that the semiconductor wafer is stopped for imaging increases and the number of times of image processing increases, resulting in an inspection time. There is a problem that becomes longer.

  Moreover, in the conventional surface inspection apparatus, although the irradiation direction of the inspection light within the surface of the semiconductor wafer is changed by rotating the semiconductor wafer, the incident angle of the inspection light with respect to the surface of the semiconductor wafer is fixed. For this reason, in the conventional surface inspection apparatus, there is a possibility that there is a defect that cannot be captured yet, no matter how small the rotation angle pitch of the semiconductor wafer is, as described above.

In order to solve such a problem, one having a tilt mechanism capable of changing the tilt of a semiconductor wafer is known. By such a tilt mechanism, even if the position of the light source is fixed, the irradiation direction of the inspection light can be changed in a plane perpendicular to the surface of the semiconductor wafer. However, when such a tilt mechanism is provided, there is a problem that the structure of the surface inspection apparatus becomes complicated, and the semiconductor wafer must be inspected at a plurality of inclination angles, and the inspection time is the same as described above. There is a problem that becomes longer.
The present invention has been made to solve the above-described problems, and provides a surface inspection apparatus and method capable of efficiently and accurately detecting defects without complicating the structure. is there.

  A surface inspection apparatus according to the present invention includes a sample rotation mechanism that rotates a plate-shaped sample in a state in which the surface is directed in a predetermined direction, a drive control unit that performs drive control of the sample rotation mechanism, and a surface of the sample. An imaging device that is installed in a predetermined positional relationship and images the sample surface, a plurality of light sources that irradiate the sample surface with inspection light, and is rotated by the sample rotation mechanism under the control of the drive control means Defect detecting means for detecting defects on the sample surface from a plurality of sample images obtained by photographing the surface of the sample with the imaging device, and the plurality of light sources are optical axes of inspection light therefrom It becomes the composition installed so that is not parallel.

  In such a surface inspection apparatus, the sample surface is irradiated from a plurality of light sources without causing the optical axes to be parallel. Therefore, each defect on the sample surface has a certain angle dependency on each of the plurality of inspection lights. The light comes out with sexuality. Therefore, even if the angle dependency of the light traveling from each defect with respect to the inspection light increases, the light traveling from more defects can be simultaneously captured by the imaging device.

  Further, from the viewpoint that each inspection light can be irradiated to the sample surface under stable conditions without the intersection of the optical axis of each inspection light with the sample surface moving along with the rotation of the sample. Are preferably installed so that the optical axes of the inspection light from them intersect at the center of rotation of the sample surface.

  The plurality of light sources are installed so as to satisfy a horizontal direction condition that an angle formed by a projection line of an optical axis of each inspection light with respect to a plane parallel to the sample surface is a predetermined angle larger than zero. It can be configured to include at least a light source.

  With such a configuration, there are substantially at least two irradiation directions of the inspection light within the sample surface, so that the rotation angle pitch for rotating the sample can be further increased.

  The at least two light sources that satisfy the horizontal direction condition may be configured so that the incident angles of the inspection light from the light sources on the sample surface are the same.

  Further, in the surface inspection apparatus in which at least two light sources satisfying the horizontal direction condition are installed, the drive control means has the angle unit obtained by multiplying the predetermined angle by the number of light sources satisfying the horizontal direction condition. The sample rotation mechanism can be controlled to rotate the sample.

  With such a configuration, it becomes possible to detect a defect with the same accuracy as when the sample is rotated to the predetermined angle unit in the horizontal condition in a state where a single inspection light is irradiated on the sample surface. . That is, the angular pitch for rotating the sample can be increased.

  Further, the plurality of light sources can be configured to include at least two light sources installed so as to satisfy a vertical direction condition that incident angles of the respective inspection lights are different from each other on the sample surface.

  With such a configuration, it is possible to capture light traveling from more defects in the imaging apparatus without changing the tilt of the sample.

  The at least two light sources satisfying the vertical direction condition can be configured so that their optical axes are included in the same plane perpendicular to the sample surface.

  The defect detection means generates a composite image corresponding to a single sample image while performing angle correction from a sample image at a plurality of angular positions obtained by photographing the surface of the rotated sample with the imaging device. It can comprise so that it may have an image composition means to do.

  With such a configuration, since the portion representing each defect included in the sample image at a plurality of angular positions is aggregated in the composite image, the defect attributes (position, shape, size, number, etc.) can be determined more accurately. Will be able to.

  Further, the image composition means generates a difference image by subtracting a predetermined reference image from each of the sample images at a plurality of angular positions obtained by photographing the surface of the rotated sample with the imaging device. Image generating means, and difference image synthesizing means for generating the synthesized image by synthesizing the difference images at the plurality of angular positions obtained by the difference image generating means while correcting the angular positions. Can be configured.

  With such a configuration, since the difference image represents a defective portion with reference to the reference image, a composite image that expresses the defective portion more clearly can be obtained.

  As the predetermined reference image, a non-defective sample image obtained by photographing a predetermined non-defective sample with the imaging device can be used.

  With such a configuration, since the difference information represents a defective portion based on a non-defective sample image obtained by photographing the non-defective sample, a defect with respect to the non-defective sample can be easily detected.

  Further, as the predetermined reference image, an image obtained by extracting a predetermined low frequency band component from each of the sample images at the plurality of angular positions can be used.

  Since the defect is included in the sample image as a bright spot as a strong luminance level, the image obtained by extracting a predetermined low frequency band component from each of the sample images is one in which the defective portion is removed. . By using such an image as a reference image, the differential image represents the removed defective portion.

  From the viewpoint that the operator can visually confirm the state of the defect on the sample surface, the surface inspection apparatus according to the present invention can be configured to have an inspection result output means for outputting the composite image as an inspection result.

  Further, from the viewpoint that the operator can easily compare with an actual sample, the surface inspection apparatus according to the present invention is a non-defective sample image obtained by photographing the synthesized image and a predetermined good sample with the imaging device. It is possible to have an inspection result output means for outputting an image obtained by superimposing and as a defect inspection result.

  Furthermore, from the viewpoint that the operator can easily confirm the defect attribute of the sample surface, the surface inspection apparatus according to the present invention includes defect information generating means for generating information representing the attribute of the defect based on the composite image, Inspection result output means for outputting information representing the attribute of the defect as the inspection result can be provided.

  The surface inspection method according to the present invention irradiates inspection light from a plurality of light sources installed so that the optical axes are not parallel to the surface of a plate-like sample rotated with the surface directed in a predetermined direction. And it can comprise so that the defect of the said sample surface may be detected from the some sample image obtained by image | photographing the surface of the said rotated sample with an imaging device.

  Furthermore, the surface inspection apparatus according to the present invention includes a sample rotation mechanism that rotates a plate-shaped sample with the surface thereof directed in a predetermined direction, a drive control unit that performs drive control of the sample rotation mechanism, An imaging device that is installed in a predetermined positional relationship with the surface and that images the sample surface, a light source that irradiates the sample surface with inspection light, and rotation by the sample rotation mechanism under the control of the drive control means Defect detecting means for detecting defects on the surface of the sample from a plurality of sample images obtained by photographing the surface of the sample with the imaging device, and the defect detecting means is rotated on the surface of the sample. Obtained by the difference image generation means for subtracting a predetermined reference image from each of the sample images at a plurality of angular positions obtained by photographing with the imaging device, and the difference image generation means in front Configured to have an image combining means for a differential image at a plurality of angular positions by combining while performing correction of angular positions to generate a composite difference image.

  According to the present invention, since the inspection light whose optical axes are not parallel is irradiated onto the sample surface from a plurality of light sources, light from each defect on the surface of the sample has a certain angle dependency with respect to each of the plurality of inspection lights. It begins to advance. For this reason, even if the angle dependency of the light traveling from each defect on the inspection light increases, it becomes possible to simultaneously capture the light traveling from more defects in the imaging device, and no special mechanism such as a tilt mechanism is provided. However, it is possible to detect defects on the surface of the sample with high accuracy without rotating the sample at a smaller angular pitch. That is, it is possible to realize a surface inspection apparatus and method that can detect defects efficiently and more accurately without complicating the structure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
A basic configuration of a surface inspection apparatus according to an embodiment of the present invention is as shown in FIG. This surface inspection apparatus detects defects on the surface of a semiconductor wafer as a sample to be inspected.

  In FIG. 1, the surface inspection apparatus includes a cassette 200 storing a semiconductor wafer 10 to be inspected, a sample loading robot mechanism 300, an aligner 100, and a sample unloading robot 400. The aligner 100 is provided with a turntable 20 (corresponding to a sample rotating mechanism) that holds and rotates a predetermined position of the periphery of the semiconductor wafer 10 as a sample. With such a configuration, the semiconductor wafer 10 taken out from the cassette 200 by the sample carry-in robot mechanism 300 is set on the turntable 20, and the surface defects of the semiconductor wafer 10 are inspected. After the inspection is completed, the semiconductor wafer 10 is taken out from the turntable 20 by the sample carry-out robot mechanism 400 and moved to a visual inspection table (not shown).

  In the surface inspection apparatus, an imaging camera 30 such as a CCD camera (corresponding to the imaging apparatus), a black shade 40, and a light source unit 50 (corresponding to the light source) are further disposed above the turntable 20. A specific support structure for the imaging camera 30, the shade 40, and the light source unit 50 will be described later. The imaging camera 30 is arranged so that the surface of the semiconductor wafer 10 on the turntable 20 can be photographed through a hole formed in the shade 40. The light source unit 50 is arranged so as to irradiate the inspection light from obliquely above the semiconductor wafer 10 on the turntable 20. On the opposite side of the light source unit 50 across the turntable 20, a reflection mirror 60 is installed with a predetermined inclination. As a result, when the inspection light emitted from the light source unit 50 is specularly reflected on the surface of the semiconductor wafer 10, the reflected light enters the reflection mirror 60 and escapes in a predetermined direction, and the dark field with respect to the imaging camera 30. The environment is to be preserved.

  The imaging camera 30 is connected to an inspection processing apparatus 500 (having a function corresponding to a defect detection means). The inspection processing apparatus 500 generates image data representing the surface of the semiconductor wafer 10 from an imaging signal from the imaging camera 30 that images the surface of the semiconductor wafer 10, and processes the image data according to a predetermined procedure to thereby detect the surface of the semiconductor wafer 10. Information representing the defect is generated. Specific configuration and processing of the inspection processing apparatus 500 will be described later.

The processing system of the surface inspection apparatus configured as described above is configured as shown in FIG.
In FIG. 2, this processing system includes the inspection processing device 500 described above, the robot control device 600 that performs drive control of the sample carry-in robot mechanism 300 and the sample carry-out robot mechanism 400, and the turntable drive that performs drive control of the turntable 20. A control device 700 (corresponding to drive control means) and a general control device 800 are provided. The overall control unit 800 performs overall control such as timing control for the inspection processing device 500, the robot control device 600, and the turntable drive control device 700.

  The inspection processing apparatus 500 includes an image processing unit 501, an input processing unit 502, a memory unit 503, and a monitor unit 504. The input processing unit 502 performs processing such as conversion from a photographing signal sent serially in pixel units from the imaging camera 30 to parallel image data in pixel units. The image processing unit 501 processes the image data sent from the input processing unit 502 according to a predetermined procedure, and extracts defects on the surface of the semiconductor wafer 10. The memory unit 503 stores various image data during the process of the image processing unit 501. The monitor unit 504 displays various information representing defects on the surface of the semiconductor wafer 10 obtained by the processing in the image processing unit 501.

  The turntable drive control device 700 has a stepping motor 701 and a drive circuit 702. Based on a timing control signal from the overall control device 800, the drive circuit 702 rotates the stepping motor 701 by a predetermined angle unit. As the stepping motor 701 rotates, the turntable 20 rotates.

  Specific support mechanisms for the above-described imaging camera 30, shade 40, and light source unit 50 will be described with reference to FIGS. 3, 4, and 5. FIG. 3 is a view of the support mechanism as viewed from the side, FIG. 4 is a view of the support mechanism as viewed from above, and FIG. 5 is a view of the support mechanism as viewed from the front.

  The front columns 41 and 43 and the rear columns 42 and 44 are erected on the apparatus installation surface so that the aligner 100 is disposed in a space surrounded by the front columns 41 and 43 and the rear columns 42 and 44. The camera mounting member 35 is fixedly supported by the front columns 41 and 43 and the rear columns 42 and 44. A shade 40 is attached to the surface of the camera mounting member 35 that faces the aligner 100. The imaging camera 30 is arranged and fixed on the upper surface side of the camera mounting member 35 so that the focal point of the optical system is the rotation center of the semiconductor wafer 10 to be set on the turntable 20 on the aligner 100.

  One end of the overhanging arm members 45, 46 is fixed to the front struts 41, 43, and the other end of the overhanging arm members 45, 46 is connected and fixed by a connecting member 47. One end of the arc-shaped first light source mounting plate 48 is fixed to the camera mounting member 35 by a fixing tool 36, and the other end is fixed to the joint between the overhang arm member 45 and the connecting member 47. An arc-shaped second light source mounting plate 49 is disposed so as to be substantially parallel to the first light source mounting plate 48, and one end of the second light source mounting plate 49 is attached to the camera mounting member 35 by the fixture 36. The other end is fixed to the joint between the overhanging arm member 46 and the connection member 47.

  The light source unit 50 includes four light sources 51a, 51b, 52a, and 52b. The light sources 51 a and 51 b are attached to the first light source attachment plate 48, and the light sources 52 a and 52 b are attached to the second light source attachment plate 49, respectively, with respect to the surface of the semiconductor wafer 10 set on the turntable 20. Irradiate with inspection light. In addition, a reflection mirror 60 is provided on a support member 65 outside a region surrounded by the front columns 41 and 43 and the rear columns 42 and 44 on the opposite side across the turntable 20 of the light sources 51a, 51b, 52a, and 52b. It is fixed with a tilt. As a result, the inspection light emitted from each of the light sources 51a, 51b, 52a, 52b is incident on the reflected light reflecting mirror 60 when it is specularly reflected on the surface of the semiconductor wafer 10, and escaped in a predetermined direction. The reflected light is prevented from entering the area surrounded by the front columns 41 and 43 and the rear columns 42 and 44.

  The arrangement of the four light sources 51a, 51b, 52a, 52b will be described in more detail.

  The four light sources 51a, 51b, 52a, 52b have their optical axes OA1a, OA1b, OA2a, OA2b that are not parallel to each other and intersect at the rotation center of the surface of the semiconductor wafer 10 set on the turntable 20. Are arranged as follows. Further, the positional relationship between the light source 51a attached to the first light source attachment plate 48 and the light source 52a attached to the second light source attachment plate 49 is as shown in FIG.

  In FIG. 6, the angle formed by the projection line of the optical axis OA1a of the light source 51a and the projection line of the optical axis OA2a of the light source 52a with respect to a plane parallel to the surface of the semiconductor wafer 10 set on the turntable 20 is set to α. This angle α is adjusted by adjusting the distance between the first light source mounting plate 48 and the second light source mounting plate 49, and is set to 5 degrees, for example. Since the first light source mounting plate 48 and the second light source mounting plate 49 are parallel, the positional relationship between the light source 51b and the light source 52b is the same as the positional relationship between the light source 51a and the light source 52a. The positional relationship between the light source 51a and the light source 52b and the positional relationship between the light source 51b and the light source 52a are the same as the positional relationship.

  That is, the four light sources 51a, 51b, 52a, and 52b are mounted and fixed to the first light source mounting member 48 and the second light source mounting member 49 so as to satisfy the above conditions (horizontal direction condition: see FIG. 6). . Since the four light sources 51a, 51b, 52a, and 52b are arranged in such a positional relationship that satisfies the horizontal condition as described above, every time the semiconductor wafer 10 is rotated by an angle (2α) that is twice the angle α. Even if the defect is detected based on the image obtained from the imaging camera 30, the image obtained from the imaging camera 30 every time the semiconductor wafer 10 irradiated with the inspection light from the single light source is rotated by the angle α. Based on this, it is possible to obtain the same accuracy as when a defect is detected. That is, the number of times the semiconductor wafer 10 is photographed can be reduced, and the inspection time can be shortened. In addition, if defects are detected by acquiring images at the same rotation angle as in the case of a single light source, it is possible to detect fine defects and improve defect detection accuracy. .

  The positional relationship between the light source 51a and the light source 51b attached to the first light source attachment plate 48 is as shown in FIG.

  In FIG. 7, the optical axis OA1a of the light source 51a and the optical axis OA1b of the light source 51b are included in the same plane (determined by the first light source mounting plate 48) perpendicular to the surface of the semiconductor wafer 10 set on the turntable 20. The incident angle γ1 of the inspection light (optical axis OA1a) irradiated from the light source 51a with respect to the surface of the semiconductor wafer 10 and the incident angle γ2 of the inspection light (optical axis OA1b) irradiated from the light source 51b with respect to the surface of the semiconductor wafer 10 are Different. In general, the incident angle with respect to the plane of the light beam is defined by an angle formed by the normal line of the light beam and the plane. In FIG. 7, the optical axis OA1a of the light source 51a and the optical axis OA1b of the light source 51b are the semiconductor wafer. 10 are included in the same plane perpendicular to the surface, their incident angles are represented by angles formed by the optical axis and the surface of the semiconductor wafer 10.

  The positional relationship between the light source 52a and the light source 52b attached to the second light source mounting plate 49 is the same as the positional relationship between the light source 51a and the light source 51b shown in FIG. However, the incident angle of the inspection light irradiated from the light source 52a with respect to the surface of the semiconductor wafer 10 is different from the incident angle (γ1) of the inspection light irradiated from the light source 51a, and the semiconductor wafer of the inspection light irradiated from the light source 52b. The incident angle with respect to the surface 10 is different from the incident angle (γ2) of the inspection light emitted from the light source 51b (see FIG. 3). The incident angle of the inspection light emitted from the light source 52a is set to be the same as the incident angle (γ1) of the inspection light emitted from the light source 51a, and the incident angle of the inspection light emitted from the light source 52b is set as the light source. It can also be set to be the same as the incident angle (γ2) of the inspection light irradiated from 51b.

  That is, each light source 51a, 51b, 52a, 52b is attached to the first light source mounting member 48 and the second light source mounting member 49 so as to satisfy the above-described incident angle condition (vertical direction condition: see FIG. 7). Installation fixed. Since the four light sources 51a, 51b, 52a, and 52b are arranged in such a positional relationship that satisfies the vertical condition as described above, the semiconductor wafer can be obtained with the same accuracy without providing the tilt mechanism of the semiconductor wafer 10. 10 surface defects can be detected.

  Next, a process for detecting defects on the surface of the semiconductor wafer 10 will be described. The inspection light from the four light sources 51a, 51b, 52a, and 52b arranged as described above is irradiated on the surface of the semiconductor wafer 10 set on the turntable 20 from the overall control device 800 (see FIG. 2). Based on the timing control signal, the stepping motor 701 of the turntable drive control device 700 rotates in units of angle 2α which is twice the angle α representing the positional relationship between the light source 51a and the light source 52a (light source 51b and light source 52b). Is done. By driving the stepping motor 701, the semiconductor wafer 10 is rotated in units of the angle 2α. The imaging camera 30 captures the surface of the semiconductor wafer 10 at each angular position with an interval of the angle 2α. Then, the inspection processing apparatus 500 captures a shooting signal from the imaging camera 30 under the control of the overall control apparatus 800.

  In the inspection processing apparatus 500, the input processing unit 502 converts a photographing signal from the imaging camera 30 into image data representing a luminance level in units of pixels and supplies the image data to the image processing unit 501. The image processing unit 501 converts the image data from the input processing unit 502 into image data for one frame representing an image on the surface of the semiconductor wafer 10 and stores the image data in the memory unit 503 as original image data. By performing such processing in synchronization with the rotation of the turntable 20, original image data representing the image of the surface of the semiconductor wafer 10 captured by the imaging camera 30 at each angular position is stored in the memory unit for the number of times N. 503 is accumulated.

  When the inspection light from the four light sources 51a, 51b, 52a, 52b is irradiated to a defect (such as a scratch) on the surface of the semiconductor wafer 10, the irradiation direction (of the optical axis) of each of the four inspection lights from the defect. Four light beams that have intensity distributions that are biased in a certain direction with respect to (direction). In this way, light advances from each defect in a direction (intensity distribution peak direction) depending on each of the irradiation directions of the four inspection lights, and thus there is a probability that light from each defect can be captured by the imaging camera 30. Get higher. Then, when any of the light beams that have advanced from the defect enters the imaging camera 30, the luminance level of the pixel corresponding to the position of the scratch in the original image data generated based on the imaging signal from the imaging camera 30 Becomes higher than the luminance level of other pixels.

  As described above, when the original image data corresponding to the N original images is accumulated in the memory unit 503, the image processing unit 501 performs processing according to the procedure shown in FIG.

  In FIG. 8, the image processing unit 501 acquires I-th (initial value 1) original image data Ri stored in the memory unit 503 (S1). The memory unit 503 stores non-defective image data obtained by photographing the surface of a semiconductor wafer determined to be non-defective in advance (hereinafter, various image data are simply expressed as images in the description of this processing). The image processing unit 501 creates a difference image Si between the acquired original image Ri and a non-defective image (corresponding to the reference image) (S2: function corresponding to difference image generating means and difference image generating step). Specifically, the luminance level of the corresponding pixel of the non-defective image is subtracted from the luminance level of each pixel of the original image Ri. A difference image Si is formed by each pixel of the luminance level obtained as a result of the subtraction. Therefore, pixels having a relatively high luminance level in the difference image Si are expected to correspond to defects that are not present in the non-defective images. The difference image Si created in this way is stored in the memory unit 503.

  The image processing unit 501 performs a threshold process on the luminance level of each pixel of the difference image Si obtained as described above, thereby removing a noise and an area having a luminance level that is expected to correspond to a defect. (A set of pixels) is extracted (S3). Thereafter, the image processing unit 501 designates the next original image (I = I + 1) until it determines that the processing for all the original images (N original images) accumulated in the memory unit 503 has been completed (S4). Then, the same processing (generation of the difference image Si) as described above is repeatedly executed on the original image (S1, S2, S3, S4).

  When it is determined that the processing for all the original images stored in the memory unit 503 has been completed (YES in S4), the image processing unit 501 stores the N sheets stored in the memory unit 503 at that time. The difference images are combined to generate a combined difference image (S5: function corresponding to image combining means and image combining step). Specifically, the angle adjustment of each difference image is performed based on the angle position when the original image corresponding to each difference image is obtained. Then, a luminance level equal to or higher than a predetermined threshold is extracted from the luminance levels of N pixels at the same position in each difference image, and the maximum level among the extracted luminance levels is determined as the luminance level for the pixel at that position. By performing such processing, necessary defect information can be taken into the composite image without deteriorating.

  When the composite difference image is generated as described above, the image processing unit 501 extracts a defective area from the composite image. (S6). The process for extracting the defective area is performed as follows. A pixel having a first luminance level L1 or higher is searched. Further, with that pixel as a nucleus, a pixel collection region that is equal to or higher than the second luminance level L2 (<L1) smaller than the first luminance level is detected as a defective region. As a result, noise (smaller than the second luminance level L2) can be removed, and the accurate size of the defect (a region having a peak equal to or higher than the second luminance level L2) can be measured.

  Next, the image processing unit 501 determines the position of the defect existing on the surface of the semiconductor wafer from the defect area (a set shape of pixels) extracted from one composite difference image corresponding to one semiconductor wafer as described above. Defect information (text data) representing the shape, size, number, etc. is created (S7). Then, the image processing unit 501 sends the defect information to the monitor unit 504, and the attribute (position, shape, size, number, etc.) of the defect on the surface of the semiconductor wafer 10 inspected by the monitor unit 504 is, for example, a tabular format. Is displayed. The operator can determine the quality of the semiconductor wafer 10 to be inspected by looking at the defect information displayed on the monitor unit 504.

  The image processing unit 501 can further send the composite difference image obtained in the above-described process (S5) to the monitor unit 504, and cause the monitor unit 504 to display the composite difference image. In this case, the operator can visually recognize a highly likely area as a defective area. In addition, the image processing unit 501 can generate a composite image obtained by superimposing the composite difference image and the above-described non-defective image, send the composite image to the monitor unit 504, and cause the monitor unit 504 to display the composite image. In this case, the operator can easily perform visual inspection of the semiconductor wafer 10 by comparing the state of the semiconductor wafer 10 to be actually inspected with the composite image displayed on the monitor unit 504.

  In the processing in the image processing unit 501 as described above, information on defects included in a difference image representing a difference between each original image and a non-defective image is combined with all the difference images to generate a combined difference image. By doing so, it becomes possible to express with connection and spread. For this reason, it is possible to detect defects with higher accuracy. Furthermore, since it is only necessary to extract a defect from one composite difference image, the processing is also simplified.

  In the example described above, the light source unit 50 is configured by the four light sources 51a, 51b, 52a, and 52b, but the configuration of the light source unit 50 is not limited to this. Five or more light sources can also be arranged. However, the number of light sources is determined within a range that can maintain a dark field environment determined by the relationship between the performance of the imaging camera 30 and the inspection accuracy. In particular, the number of light sources arranged along the surface of the semiconductor wafer 10 is liable to affect the dark field environment, so it is not preferable to increase the number of light sources.

  In the above-described example, the non-defective image is used to obtain the difference image. However, the image (reference image) serving as a reference for obtaining the difference image is not limited to this. For example, an image obtained by extracting a predetermined low frequency band component from the original image can be used as the reference image. In general, a portion corresponding to a defect in the original image appears as a bright spot, and therefore the frequency component becomes very high. Therefore, the component corresponding to the defect is not included in the predetermined low frequency band component extracted from the original image, and is suitable as a reference image for generating a difference image.

  The arrangement relationship of the plurality of light sources is not particularly limited as long as the inspection light from each light source is irradiated on the surface of the semiconductor wafer 10 to be inspected in a state where the optical axes are not parallel. For example, the light source 51a and the light source 52b or the light source 51b and the light source 52a may be arranged in an oblique manner.

It is a figure which shows the basic composition of the surface inspection apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the structural example of the processing system of the surface inspection apparatus shown in FIG. It is FIG. (1) which shows the support mechanism of an imaging camera, a shade, and an optical unit. It is FIG. (2) which shows the support mechanism of an imaging camera, a shade, and an optical unit. It is FIG. (3) which shows the support mechanism of an imaging camera, a shade, and an optical unit. It is a figure which shows the optical conditions (the 1) which should satisfy | fill each light source in the surface inspection apparatus shown in FIG. It is a figure which shows the optical conditions (the 2) which should satisfy | fill each light source in the surface inspection apparatus shown in FIG. 2 is a flowchart showing a processing procedure for detecting defects on the surface of a semiconductor wafer in the surface inspection apparatus shown in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Semiconductor wafer 20 Turntable 30 Imaging camera 35 Camera attachment member 36 Fixture 40 Shade 41, 43 Front support | pillar 42, 44 Back support | pillar 45, 46 Overhang | projection arm member 47 Connection member 48 1st light source attachment plate 49 2nd light source attachment Plate 50 Light source unit 51a, 51b, 52a, 52b Light source 60 Reflecting mirror 65 Supporting tool 100 Aligner 200 Cassette 300 Sample loading robot mechanism 400 Sample unloading robot mechanism 500 Inspection processing device 501 Image processing unit 502 Input processing unit 503 Memory unit 504 Monitor unit 600 Robot control device 700 Turntable drive control device 701 Stepping motor 702 Drive circuit 800 Overall control device

Claims (2)

A sample rotation mechanism for rotating a plate-shaped sample with its surface facing a predetermined direction;
Drive control means for performing drive control of the sample rotation mechanism;
An imaging device installed in a predetermined positional relationship with respect to the surface of the sample and photographing the surface of the sample;
A light source for irradiating the sample surface with inspection light;
Defect detection means for detecting defects on the sample surface from a plurality of sample images obtained by photographing the surface of the sample rotated by the sample rotation mechanism under the control of the drive control means with the imaging device; Prepared,
The defect detection means generates a difference image by subtracting a predetermined reference image from each of the sample images at a plurality of angular positions obtained by photographing the surface of the rotated sample with the imaging device. Means,
A surface inspection apparatus comprising: an image synthesis unit configured to synthesize a difference image obtained at the plurality of angular positions obtained by the difference image generation unit while correcting the angular position to generate a synthesized difference image. Rotate the plate-shaped sample with its surface facing the specified direction,
Photographing the sample surface with an imaging device in a state in which the inspection light is irradiated on the sample surface,
A surface inspection method for detecting defects on the sample surface from a plurality of sample images obtained by photographing the surface of the rotated sample with the imaging device,
A difference image generation step of generating a difference image by subtracting a predetermined reference image from each of the sample images at a plurality of angular positions obtained by photographing the surface of the rotated sample with the imaging device;
An image synthesis step of generating a synthesized difference image by synthesizing the difference images at the plurality of angular positions obtained in the difference image generating step while correcting the angular position;
A surface inspection method for detecting defects on the surface of the sample from the composite difference image.

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