JPH11326228A - Mirror surface body visual inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To visually inspect a mirror surface according to an image with an improved S/N ratio. SOLUTION: A wafer W, a lens 5 of an image pick-up optical system, and a high-resolution image pick-up element 6 are arranged in parallel one another, thus obtaining the image of the wafer W with the high-resolution image pick-up element 6. A bright visual field lighting system 8 shows a white plate 11 on the mirror surface of the wafer W and picks up the image of the mirror surface of the wafer W with an improved S/N ratio by an image pick-up camera 4. A dark visual field lighting system 9 directly applies light to the wafer W by appropriately using a light projection type lighting device 12, a surface- lighting device 16, a side-lighting device 18, and an annular lighting device 20 with a small lighting angle. By picking up images in bright visual field lighting and dark visual field lighting, a defect can be easily evaluated and judged.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a specular surface appearance inspection apparatus used for inspecting a mirror surface of a semiconductor wafer or the like having a mirror surface.

[0002]

2. Description of the Related Art A semiconductor wafer is cut into a wafer shape from an ingot of silicon or the like, and is mirror-polished and finished as a mirror. A surface defect of the semiconductor wafer as the mirror is inspected. As this surface defect,
There are three-dimensional or planar defects such as dust, scratches, dirt, and pinholes, and these defects are usually inspected by visual inspection or automatic inspection. The visual inspection has a problem that it is complicated and time-consuming. When the inspection is performed by the automatic inspection, for example, a television camera system and a laser scanning system are performed. In the case of the TV camera system, for example, the irradiation light from the light source of the illumination optical system is radiated to the surface of the wafer as a projection light beam by a collimator mirror or the like, and this is used as a dark-field illumination by a high-sensitivity imaging camera from above the illumination optical path from above. Image data is obtained by imaging. Defects such as dust and scratches on the wafer are captured as bright images by scattered light, and can be detected by visual observation and as digital signals.

In the laser scanning method, a laser beam is moved in the XY direction as a spot beam, for example, to move on the wafer surface. If there is a defect, the beam becomes scattered light or diffracted light. Is detected as a defect by receiving light by a light receiving element or the like.

[0004]

However, in the case of the above-described television camera system, when imaging under dark-field illumination, the television camera is positioned obliquely upward with respect to the wafer to perform imaging. On the other hand, since the imaging lens system of the television camera and the imaging device are arranged in a non-parallel manner, the entire wafer is not at the in-focus position, and there is a disadvantage that defects cannot be detected over the entire surface of the wafer. If the depth of focus of the imaging optical system of the TV camera is increased to improve this, if the object to be inspected is a mirror-like object such as a wafer, the light source of the illumination system will appear in the wafer image and accurate imaging data will be obtained. There is a problem that it cannot be obtained. When a wafer is imaged using a general bright-field illumination system, a half mirror is provided between the light source and the wafer, and the wafer is imaged by incident illumination of the wafer through the half mirror. However, if the object to be inspected is a mirror-like object such as a wafer, the light source and the lens etc. reflected on the mirror surface of the wafer appear in the image of the wafer to be imaged. There is a problem that can not be.

Further, in the case of the laser scanning method, since the spotlight for inspection is small, the wafer to be inspected has a relatively large area, and it is required to increase the scanning speed and lengthen the inspection. In addition, it is difficult to distinguish defects such as flaws and stains from the detected data, and it is difficult to obtain a variety of information from a plurality of types of images with different illumination conditions. As described above, in the conventional wafer inspection apparatus, the S / N ratio between the normal surface and the defect is poor, and the inspection and determination of various defects existing on the wafer surface, such as scratches, dust, dirt, and pinholes, can be performed in a short time. There was a drawback that it could not be performed sufficiently.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a specular body appearance inspection apparatus capable of precisely imaging the entire mirror body in a focused state in a bright field. Another object of the present invention is to provide a specular body appearance inspection apparatus capable of discriminating various kinds of defects such as scratches, dust, and dirt on the specular body by increasing the S / N ratio between a normal surface and a defect. That is.

[0007]

According to the present invention, there is provided a mirror appearance inspection apparatus according to the present invention, wherein the mirror surface is imaged on an image sensor by an imaging camera having an imaging lens positioned obliquely to a normal to a mirror surface of the mirror body. The imaging lens, the mirror surface, and the imaging device are arranged in parallel with each other,
A bright uniform surface reflected on the mirror surface is arranged on a side opposite to the imaging lens with respect to a normal line of the mirror surface.
Therefore, the optical axis of the imaging camera is oblique to the normal of the mirror surface, and the mirror surface is projected by the imaging camera in a state where a bright uniform surface is reflected on (the entire surface of) the inspection surface of the inspection target mirror object. When an image is taken, the mirror surface is formed in an in-focus state on the image sensor through the image pickup lens over the entire surface, and furthermore, the light source unevenness is not projected on the captured image with respect to the mirror surface of the mirror body, and the S / N ratio is good. Image data of the whole body can be obtained clearly. When there is a defect on the mirror surface, a defect having a high flatness such as dirt or a pinhole cannot form a regular reflection image like a normal portion of the mirror surface, and the contrast with other normal portions is large and can be clearly detected. A bright-field image is obtained. On the other hand, in the case of a three-dimensional defect having a convex portion such as dust or a flaw, a part of the irregularly reflected light reflected at the portion is incident on the imaging lens, so that the contrast is small and relatively difficult to detect.

Further, the specular body appearance inspection apparatus according to the present invention is arranged such that the specular body is picked up by the image pickup device by the image pickup camera having the image pickup lens, and the image pickup lens, the mirror body, and the image pickup element are parallel to each other. A dark-field illumination system and a bright-field illumination system are arranged as illumination systems, and an image is captured by selectively using either the dark-field illumination system or the bright-field illumination system. An abnormal portion is detected from a plurality of images having different illuminations. In addition to the above-described imaging characteristics under bright-field illumination, when an object to be inspected is illuminated using a dark-field illumination system, the obtained captured image is black on a normal mirror surface without defects, and dust and scratches. Such a three-dimensional defect becomes a bright image because part of the illumination light is reflected and enters the imaging lens, and can be clearly identified. On the other hand, defects having no or small projections such as dirt and pinholes cannot be clearly identified because the amount of light incident on the imaging lens due to irregular reflection is small. Therefore, the object to be inspected is illuminated by selectively using a bright-field illumination system and a dark-field illumination system according to the type of defect to be determined, and images under each illumination are taken. If the information is detected, various types of defects can be clearly caught and can be easily determined.

[0009]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIGS. FIG. 1 is a configuration diagram of a main part of a visual inspection device according to an embodiment of the present invention, FIG. 2 is a configuration diagram showing a bright-field imaging system of the visual inspection device shown in FIG. 1, and FIG. FIG. 2 is a configuration diagram illustrating a dark-field imaging system. In a visual inspection apparatus 1 shown in FIG. 1, a turntable 3 for supporting a semiconductor wafer (hereinafter, referred to as a wafer) W as an object to be inspected is provided on a base 2 so as to be rotatable around its center line. The surface of the wafer W is mirror-polished. Further, an imaging camera 4 for mirror-surface imaging for observing the surface of the wafer W obliquely above the wafer W for defect inspection is provided. The imaging camera 4 includes a wide-angle imaging lens 5 as an imaging lens system, and a high-definition imaging element 6 is provided as an imaging element on a focal plane which is an image forming position of the wafer W through the lens 5. Have been. The lens 5 is composed of, for example, a biconvex lens and has a major axis a and a minor axis b orthogonal to each other, and the minor axis b of the lens 5 is the principal axis of the imaging optical system, and the major axis a is orthogonal to the principal axis. Surface of wafer W and high-definition image sensor 6
And are arranged in parallel. Moreover, this imaging optical system
The optical axis L is configured to connect the center point of the wafer W and the center point of the high-definition image sensor 6 through the intersection of the major axis a and the minor axis b of the lens 5. Therefore, the lens 5 is disposed coaxially and parallel to the surface of the wafer W and the high-definition image sensor 6, and the optical axis L obliquely intersects the lens 5, the surface of the wafer W, and the high-definition image sensor 6. Become.

The appearance inspection apparatus 1 is provided with a bright-field illumination system 8 and a dark-field illumination system 9 as illumination systems. In the bright field illumination system 8, as shown in FIGS. 1 and 2, for example, a panel-shaped light source 10 is disposed at a position and an angle at which light does not directly enter the wafer W, and a white plate 11 is opposed to the light source 10. (A uniform surface) is provided, and the white plate 11 receives the light beam emitted from the light source 10 and irradiates the wafer W as uniform reflected light. Here, various light sources such as an incandescent lamp and a fluorescent lamp can be used as the light source 10, and the white plate 11 can irradiate the irradiation light from the light source 10 as uniform reflected light so that the light is reflected even on the wafer W. It is sufficient that the surface is uniform without unevenness, and for example, frosted glass, Kent paper, milky white plate and the like are used. Then, the image of the bright white plate 11 reflected on the mirror surface of the wafer W is formed in an out-of-focus state on the high-definition image pickup device 6 by the imaging camera 4 via the imaging optical system including the lens 5.

Next, as a dark field illumination system 9, for example, as shown in FIGS. 1 and 3, a first illumination system, a second illumination system, a third illumination system, and a fourth illumination system are provided. Is controlled so as to irradiate the wafer W directly selectively or simultaneously at a plurality of times. The first illumination system is, for example, a wafer W
, A first light source 13 such as a halogen lamp is positioned above a wafer W, and a substantially hemispherical surface is formed on the back surface thereof. Is provided, and a light beam emitted from the first light source 13 illuminates the wafer W via the condenser lens 15. In addition, the wafer W of this illumination light
Is reflected in a direction away from the imaging camera 4. The second illumination system is a surface illumination device 16 disposed above the wafer W.
Above the wafer W and the projection type lighting device 12
For example, a panel-type second light source 17 is provided around the condenser lens 15 of the above, and the entire surface of the wafer W is directly radiated from the second light source 17. The light is reflected in a direction away from the camera 4.

The third illuminating system is one or a plurality of side illuminating devices 18 disposed obliquely above the wafer W outside the illumination optical paths of the first and second illuminating systems. A third light source 19, such as a high-frequency fluorescent lamp, illuminates the wafer W obliquely from above, and is reflected in a direction away from the imaging camera 4 on a normal surface. The fourth illumination system is disposed at a position lower than the height of the first, second, and third illumination systems over the entire outer periphery of the wafer W, and emits light at a smaller inclination angle than other dark field illumination systems. A lighting device 20 for illuminating the wafer W by means of a ring-shaped fourth light source 20a such as a circular high-frequency fluorescent lamp or a low-angle large-diameter LED ring lighting. When W is illuminated, the light reflected on the normal surface is reflected in a direction away from the imaging camera 4. Further, a light-shielding reflection plate 27 is provided on the entire back surface of the fourth light source 20a so that the irradiation light of the fourth light source 20a does not enter the imaging camera 4.
Therefore, in the present embodiment, the bright-field illumination system 8 including one type of illumination device and the four types of illumination devices 12, 16, 1
And a dark-field illumination system 9 consisting of 8, 20 as appropriate.
Alternatively, a plurality of wafers W are simultaneously illuminated. The high-definition image pickup element 6 of the imaging camera 4 is connected to a defect detection circuit 22 having a plurality of image memories in a defect detection control means 21 as shown in FIG. Various defects on the wafer W, such as scratches, dust, dirt, and pinholes, are detected based on the obtained image signals by, for example, correlation processing of signal patterns and images, and the like. C is for performing arithmetic processing such as specifying the position of a defect on the wafer W.
A PU 23 is connected, and the CPU 23 has a CRT 24 for displaying a defect detection image and a printer 2 for outputting an inspection result.
5 etc. are connected.

The appearance inspection apparatus 1 according to the present embodiment is configured as described above. Next, a description will be given of a method of inspecting a defect of a wafer W using these bright and dark field illumination systems.
First, the appearance of the wafer W is inspected using the bright-field illumination system 8 shown in FIG. In the bright-field illumination system 8, the irradiation light of the bright-field light source 10 is radiated to the white plate 11 and scattered due to minute irregularities on the reflection surface of the white plate 11, so that the unevenness of the bright-field light source 10 is eliminated. The brightness becomes uniform. Therefore, the light source unevenness does not appear in the image of the white plate reflected on the wafer W. In addition to this, in the present imaging optical system, the depth of focus is made shallow, so that the entire surface of the wafer W is in focus. It is possible to capture an image in which the entire mirror is in focus and the entire surface of the wafer W is in focus and the normal mirror surface is in a uniform bright field. The surface of the wafer W is imaged by a high-definition image sensor 6 via an imaging optical system including a lens 5 by an imaging camera 4 arranged obliquely on the opposite side of the white plate 11 with respect to a normal line of a mirror surface as an inspection surface. Imaged on top.
At this time, since the mirror surface of the wafer W and the image forming surface of the high-definition image pickup device 6 are arranged in parallel with the long axis a of the lens 5, the entire surface of the wafer W is in focus, and The entire wafer is imaged on the image plane of the definition image pickup element 6. At that time, the light source unevenness and the like are not displayed on the imaging screen.

An image signal on the surface of the wafer W obtained by the high-definition image pickup device 6 is detected by a defect detection circuit 22 having a plurality of image memories in the control means 21 by image signal processing or the like. In the captured image under bright-field illumination, the wafer W
A normal mirror surface portion having no defect on the surface is specularly reflected by the incident light and received by the high-definition image pickup device 6 with uniform illuminance, but has a small defect such as dirt or a pinhole. In this case, normal reflection does not occur at this portion, and the amount of light incident on the high-definition image pickup element 6 is reduced, so that the brightness on the captured image is small. As shown in FIG. 4, the defective portion appears as a dark image and is detected as a defect. Is done.

Defects such as dirt and pinholes on the surface of the wafer W can be relatively easily detected under a bright-field illumination system due to the difference in the amount of light entering the high-definition image pickup device 6. In the captured image shown in FIG. 4, m1 is a stain, m2 is a fingerprint, m3
Is a scratch. However, three-dimensional defects having projections protruding from the wafer surface, such as dust and scratches, have a small contrast on the imaging screen because part of the light is incident on the imaging camera 4 when light is irregularly reflected on the surface. It is relatively difficult to obtain a clear defect image on the image. Moreover, since the degree of detection differs depending on the size of scratches or dust, clear detection is difficult to perform. However, since the image is darker than the normal portion, it is easy to detect that the image is not a normal surface (some sort of abnormal portion). Each of the obtained images is displayed on the CRT 24 as a composite image of a defect on the surface of the wafer W or for each individual image.

Further, in order to clearly inspect the wafer W for scratches, dust and the like, an external appearance inspection of the wafer W is performed using the dark field illumination system 9 shown in FIG. In the dark field illumination system 9, the first to fourth illumination systems are selectively or entirely illuminated. For example, when all of the first to fourth illumination optical systems are used, the illumination light is incident and illuminated from the first light source 13 of the floodlighting illumination device 12 to the wafer W almost directly below via the condenser lens 15 to irradiate the wafer W. Then, the reflected light is emitted in another direction without entering the imaging camera 4. Also,
In the surface illumination device 16 as well, the irradiation light from the panel-type second light source 17 is applied to the wafer W from almost directly above, and further in the side illumination device 18 the illumination light is applied to the wafer W from obliquely above by the third light source 19. Then, the fourth light source 20 emits illumination light having a smaller inclination angle to the wafer W, and each reflected light is reflected obliquely upward and away from the imaging camera 4.

Under such dark-field illumination, the surface of the wafer W is imaged by the imaging camera 4, and an image of the wafer W is formed on the high-definition imaging device 6 via the imaging optical system including the lens 5. . At this time, the imaging camera 4 focuses on the entire surface of the wafer W, and forms an image on the imaging plane of the high-definition imaging element 6. In this case, in a captured image obtained under dark-field illumination, as shown in FIG. 5, the reflected light on the wafer W is not incident on the imaging camera 4 in a normal mirror surface portion without a defect or the like on the surface of the wafer W. However, if there is a defect such as a scratch or dust on the wafer W, the wafer W is irregularly reflected and a part of the reflected light is incident on the imaging camera 4, so that the scratch or dust is bright. Can be identified as an image. In FIG. 5, n1 is a flaw. In particular, when a defect such as dust or a scratch is three-dimensional, it can be obtained as a captured image having a large S / N ratio under dark-field illumination. Regarding the pinhole defect, when the reflection surface incident on the imaging camera 4 partially appears around the pinhole,
Although the light reflected by the reflecting surface can be received and identified by the imaging camera 4, the identification becomes difficult when the light reflected by the dark-field illumination is small. Dirt, which is a planar defect that can be relatively clearly identified by bright-field illumination, and pinholes with small irregularities, are relatively difficult to identify by dark-field illumination.

In imaging under dark-field illumination, it is sometimes difficult to detect a directional defect by illumination from one direction.
Is irradiated from different directions, and by capturing these images, the defect can be detected more reliably. And a defect detection circuit 2 having a plurality of image memories.
In step 2, the position of the defect detected on the wafer W can be calculated and detected by the CPU 23 based on the relationship between the detected defect of each image and the rotational position of the wafer W, and the position, size, type, etc. of the defect can be more reliably determined. Can be detected. The image data in which the defect is detected is synthesized by the CPU 23 as a synthetic image of the defect on the surface of the wafer W, or is selectively displayed for each image on the CRT 24 or the like. Then, various types of defects that are comprehensively detected from the captured image obtained under the bright-field illumination and the captured image obtained under the dark-field illumination are evaluated and determined, synthesized, and placed on the wafer W on the CRT 24 or the like. It may be displayed. As for dark field illumination, a specific defect can be detected by selectively using any one or a plurality of the first to fourth illumination systems.

As described above, according to the present embodiment, the lens 5 and the high-definition image pickup element 6 of the image pickup optical system are disposed in parallel with the mirror surface (image pickup surface) of the wafer W, and are disposed at the in-focus position. Therefore, a clear captured image can be obtained over the entire wafer W. In addition, the bright field illumination system 8 using the white plate 11 can clearly image the mirror surface, which is the surface of the wafer W,
At this time, the mirror surface of the wafer W is focused on, and the mirror surface on which the white plate 11 is projected does not show unevenness of the light source or the like in the captured image. Can be. Further, according to the appearance inspection device 1 of the present embodiment, by picking up an image by selectively using the bright-field illumination system 8 and the dark-field illumination system 9 as the illumination optical system, it is possible to remove dirt and pinholes from the captured image. Planar defects and three-dimensional defects such as dust and scratches can be detected favorably.

In the above-described embodiment, four types of first to fourth illumination optical systems are provided as the dark-field illumination system 9, but only some of these illumination systems are provided. You may. Further, although the white plate 11 of the bright field light source 10 is used for the bright field illumination system 8, a uniform surface light emitter may be used instead.

[0021]

As described above, the specular body appearance inspection apparatus according to the present invention has the mirror surface connected to the image sensor by the imaging camera having the imaging lens positioned obliquely to the normal of the mirror surface of the mirror body. The imaging lens, the mirror surface, and the image sensor are arranged in parallel with each other, and a bright uniform surface reflected on the mirror surface is arranged on the opposite side of the imaging lens with respect to the normal line of the mirror surface. Therefore, image data of the entire mirror surface of the mirror can be obtained in an in-focus state, the image of the light source is not projected on the captured image, the S / N ratio is good, and the image data of the entire mirror surface of the mirror is clear. As a result, when there is a defect on the object to be inspected, a defect having a high flatness such as a stain or a pinhole can be clearly detected with a large contrast with a normal mirror portion.

Further, the specular body appearance inspection apparatus according to the present invention is arranged so that the specular body is picked up by the image pickup device by the image pickup camera having the image pickup lens, and the image pickup lens, the mirror body, and the image pickup element are parallel to each other. A dark-field illumination system and a bright-field illumination system are arranged as illumination systems, and an image is captured by selectively using either the dark-field illumination system or the bright-field illumination system. Abnormal parts are detected from multiple images with different illuminations, and in addition to images captured by the bright-field illumination system, dust and scratches can be detected from images obtained by illuminating the specular body from various angles using the dark-field illumination system. The three-dimensional defect with a convex part such as can be clearly identified, and the correlation between the images of the bright-field illumination system and the dark-field illumination system is evaluated according to the type of defect to be determined, and various types of defects are evaluated. Can be easily determined and determined

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of a specular appearance inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a main part configuration diagram showing an imaging optical system using bright-field illumination in the imaging optical system of the appearance inspection apparatus shown in FIG. 1;

FIG. 3 is a main configuration diagram showing an imaging optical system using dark-field illumination in the imaging optical system of the appearance inspection apparatus shown in FIG. 1;

FIG. 4 is a partial plan view of a wafer image captured under illumination of a bright field illumination system.

FIG. 5 is a partial plan view of a wafer image captured under illumination of a dark-field illumination system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Appearance inspection apparatus 4 Imaging camera 5 Lens (imaging lens) 6 High-definition image sensor (imaging element) 8 Bright field illumination system 9 Dark field illumination system 11 White plate (uniform surface) W Semiconductor wafer (mirror body)

Claims (2)

[Claims] 1. An imaging camera having an imaging lens positioned obliquely to a normal line of a mirror surface of a mirror body, the mirror surface is arranged so as to form an image on an imaging device, and the imaging lens, the mirror surface, and the imaging device are arranged. Are arranged in parallel with each other, and on the opposite side of the imaging lens with respect to the normal of the mirror surface,
A specular body appearance inspection apparatus in which a bright uniform surface reflected on the mirror surface is arranged. 2. The image forming apparatus according to claim 1, wherein the mirror body is arranged to be imaged by an image pickup device by an image pickup camera having an image pickup lens.
The imaging lens, the mirror body, and the imaging device are arranged in parallel with each other, and a dark-field illumination system and a bright-field illumination system are arranged as illumination systems. A specular body appearance inspection apparatus configured to detect an abnormal portion from a plurality of images of different illuminations captured by selectively using any one of the illumination lights.