JP2009276207A - Surface defect inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently detect a defect, while enhancing the accuracy of defect detection. <P>SOLUTION: This surface defect inspection device is equipped with an imaging part 2 for imaging a surface 1a of an inspected object 1 and a processing part 4 for detecting a defect in the surface 1a of the inspected object 1, based on an image acquired by the imaging part 2. The imaging part 2 comprises an imaging element 11 for imaging an image formed on a light-receiving surface 11a and an optical system 12 for forming an image of the surface 1a of the inspected object 1 on the receiving surface 11a. The optical axis O of the optical system 12 is inclined, in a relation to a normal line N1 of the surface 1a of the inspected object 1. A normal line N2 of the receiving surface 11a is inclined relatively, in relation to the optical axis O of the optical system 12 so as to decrease the defocus amount of the surface 1a, which is caused by the optical system 12, of the inspected object 1 on the peripheral part of the receiving surface 11a, as compared with when the normal line N2 of the receiving surface 11a is set parallel with respect to the optical axis O of the optical system 12. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface defect inspection apparatus for detecting defects on the surface of an inspection object such as a substrate.

  Conventionally, when detecting defects on the surface of an inspected object such as a substrate, the surface of the inspected object is processed by imaging the surface of the inspected object with an imaging unit such as a CCD camera and processing the image obtained from the imaging unit. (For example, the following patent document 1). An imaging unit such as a CCD camera has an imaging element such as a CCD that captures an image formed on a light receiving surface, and an optical system that forms an image of the surface of the inspection object on the light receiving surface. In the imaging unit, the optical axis of the optical system and the normal line of the light receiving surface of the imaging element are made parallel.

In this way, when the surface of the inspection object is imaged by the imaging unit and the image obtained from the imaging unit is processed to detect defects on the surface of the inspection object, the optical axis of the optical system of the imaging unit is the inspection object. In some cases, the imaging unit is arranged so as to be inclined to some extent with respect to the normal of the surface. For example, in the surface defect inspection apparatus disclosed in Patent Document 1 below, in order to irradiate the inspection object with illumination light and to capture a dark field image of the surface of the inspection object by the imaging unit, the optical system of the imaging unit The imaging unit is arranged so that the optical axis is inclined with respect to the normal line of the surface of the inspection object.
JP-A-4-344447

  However, as a result of the inventor's research, in the conventional surface defect inspection apparatus described above, the imaging unit is arranged so that the optical axis of the optical system of the imaging unit is inclined with respect to the normal line of the surface of the inspection object. As a result, it has been found that the accuracy of defect detection is reduced or defects cannot be detected efficiently.

  That is, in the conventional surface defect inspection apparatus, as described above, the optical axis of the optical system of the imaging unit is tilted with respect to the normal of the surface of the object to be inspected, and the method of the light receiving surface of the imaging element of the imaging unit The line is parallel to the optical axis of the optical system of the imaging unit. Therefore, the distance from the surface of the inspection object to the light receiving surface of the image sensor changes within the field of view of the imaging unit, and the obtained image of the surface of the inspection object is an image with a good just focus near the center. In the peripheral portion, defocusing occurs in a tilted direction. For this reason, if defect detection is performed based on the peripheral image area where defocusing occurs, the accuracy of defect detection is reduced.

  On the other hand, if defect detection is performed using only the image area near the center where an image with good focus can be obtained without using the peripheral image area where defocusing occurs, the accuracy of defect detection increases, but at one time In order to inspect the entire desired inspection area on the surface of the inspected object because the area where defects can be detected (referred to as “collective inspection area”) is narrowed, the collective inspection area is sequentially moved. As a result, the number of times that the area is imaged increases, and defects cannot be detected efficiently.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a surface defect inspection apparatus capable of efficiently detecting defects while improving the accuracy of defect detection.

  In order to solve the above problems, a surface defect inspection apparatus according to an aspect of the present invention includes an imaging unit that images the surface of an inspection object, and the surface of the inspection object based on an image obtained by the imaging unit. A processing unit that detects a defect, and the imaging unit includes an imaging element that captures an image formed on a light receiving surface, and an optical system that forms an image of the surface of the inspection object on the light receiving surface. The optical axis of the optical system is tilted with respect to the normal line of the surface of the object to be inspected, and the light receiving surface has a normal line parallel to the optical axis of the optical system. The normal line of the light receiving surface is tilted relative to the optical axis of the optical system so that the defocus amount of the surface of the inspection object by the optical system at the periphery of the surface is reduced. Is.

  ADVANTAGE OF THE INVENTION According to this invention, the surface defect inspection apparatus which can detect a defect efficiently, improving the precision of defect detection can be provided.

  Hereinafter, a surface defect inspection apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram schematically showing a surface defect inspection apparatus according to an embodiment of the present invention. FIG. 2 is a schematic enlarged view schematically showing a main part in FIG. For convenience of explanation, as shown in FIGS. 1 and 2, an X axis, a Y axis, and a Z axis that are orthogonal to each other are defined. The surface 1a of the transparent substrate 1 is parallel to the XY plane.

  The surface defect inspection apparatus according to the present embodiment is configured to inspect defects on the surface 1a on the −Z side of the transparent substrate 1 such as a glass substrate as an inspection object, and the surface 1a on the −Z side of the transparent substrate 1. A camera 2 as an image pickup unit for picking up images, an illumination optical system 3 for irradiating illumination light to the surface 1a on the −Z side of the transparent substrate 1, and the −Z side of the transparent substrate 1 based on an image obtained by the camera 2 The processing part 4 which detects the defect of the surface 1a of this, the control part 5, and the XY stage 6 as a moving mechanism are provided.

  The camera 2 captures an image formed on the light receiving surface 11a and converts it into an electrical signal, and an optical device that forms an image of the surface 1a on the -Z side of the transparent substrate 1 on the light receiving surface 11a. And an imaging lens 12 as a system. As described above, in the present embodiment, the imaging lens 12 forms an image of the surface on the −Z side of the transparent substrate 1 directly on the light receiving surface 11 a of the imaging element 11, but is not necessarily limited thereto. . For example, an image formed by the imaging lens 12 may be incident on the light receiving surface 11a of the imaging element 11 via an optical fiber bundle. In this case, the light receiving surface on which the imaging lens 12 forms an image of the surface on the −Z side of the transparent substrate 1 is the incident end surface of the optical fiber bundle. The imaging operation by the imaging element 11 is performed by a command from the control unit 5.

  The illumination optical system 3 includes a light source 13 and a collimator lens 14 that irradiates the transparent substrate 1 with light from the light source 13 as a collimator.

  In the present embodiment, the + Z side of the transparent substrate 1 is such that the illumination light from the illumination optical system 3 travels in the −Z direction, passes through the transparent substrate 1 and irradiates the −Z side surface with the illumination light. Is arranged. On the other hand, the camera 2 is arranged on the −Z side of the transparent substrate 1, and the optical axis O of the imaging lens 12 is − of the transparent substrate 1 so that the illumination light from the illumination optical system 3 does not directly enter the field of view of the camera 2. It is inclined with respect to the normal line N1 of the surface 1a on the Z side. In the present embodiment, as shown in FIGS. 1 and 2, the optical axis O of the imaging lens 12 is tilted by an angle θ in the clockwise direction in the drawing around the Y axis with respect to the normal line N1. Accordingly, a dark field image of the illuminated area by the illumination optical system 3 on the surface 1 a on the −Z side of the transparent substrate 1 is captured by the imaging element 11 of the camera 2. In the drawing, the normal line N1 is parallel to the Z axis. In the present embodiment, the area to be illuminated by the illumination optical system 3 is set to be wider than the field of view of the camera 2, but is not necessarily limited thereto. In the present embodiment, the illumination optical system 3 is disposed on the opposite side of the transparent substrate 1 from the camera 2, and the illumination optical system 3 is forward scattered light due to a defect on the surface 1 a on the −Z side of the transparent substrate 1. However, in the present invention, on the contrary, the illumination optical system 3 is disposed on the same side as the camera 2 with respect to the transparent substrate 1, and the illumination optical system 3 is the surface on the −Z side of the transparent substrate 1. You may make it catch the backscattered light by the defect of 1a. When capturing backscattered light, the inspection object may not be a transparent body such as the transparent substrate 1. In addition, it is preferable to optimize and set the angle θ so that the defect can be detected with higher sensitivity from the viewpoint of the angle dependency between the defect and the scattered light.

  In the present embodiment, the imaging lens 12 at the periphery of the light receiving surface 11a is compared with the case where the normal N2 of the light receiving surface 11a of the imaging element 11 of the camera 2 is parallel to the optical axis O of the imaging lens 12. The normal line N2 of the light receiving surface 11a is inclined relative to the optical axis O of the imaging lens 12 so that the defocus amount of the surface 1a on the −Z side of the transparent substrate 1 is reduced. In the present embodiment, as shown in FIGS. 1 and 2, the normal line N <b> 2 is inclined with respect to the optical axis O by the angle θ ′ around the Y axis in the clockwise direction in the drawing. This will be described in detail later.

  The XY stage 6 moves the entire camera 2 and illumination optical system 3 two-dimensionally in a plane parallel to the XY plane under the control of the control unit 5.

  The processing unit 4 detects a defect on the surface on the −Z side of the transparent substrate 1 based on an image (a dark field image in the present embodiment) obtained by the camera 2 under the control of the control unit 5.

  Here, an example of a specific operation of the surface defect inspection apparatus according to the present embodiment will be described. When the operation is started, first, the control unit 5 controls the XY stage 6 so that the camera 2 and the illumination optical system 3 as a whole are arranged such that the field of view of the camera 2 becomes the first inspection area of the transparent substrate 1. Move. Next, the control unit 5 causes the imaging element 11 of the camera 2 to capture a dark field image of the first inspection area of the transparent substrate 1.

  Next, the processing unit 4 processes the dark field image obtained by the imaging device 11 of the camera 2 to detect a defect. This defect detection can be performed, for example, by various known methods for detecting a defect from a dark field image. Defect detection can be performed, for example, by binarizing and labeling a dark field image obtained by the image sensor 11. At this time, it goes without saying that the accuracy of defect detection may be increased by using a pattern recognition technique or the like as necessary.

  Thereafter, the processing unit 4 determines whether or not there is an uninspected area to be inspected (an area to be inspected on the transparent substrate 1 that has not yet undergone the above-described imaging and defect detection process). If there is an uninspected area to be inspected, the control unit 5 controls the XY stage 6 so that the entire camera 2 and the illumination optical system 3 become the next inspected area of the transparent substrate 1 with the field of view of the camera 2. To move. Thereafter, the above-described imaging and defect detection process is repeated for the inspection area.

  In this way, when the above-described imaging and defect detection processing is completed for all the areas to be inspected, the processing unit 4 outputs the presence / absence of defects, the number and positions of defects, and the like as inspection results to the outside. As a result, the series of operations is completed. Note that only the presence or absence of defects may be output as the inspection result.

  As described above, the angle formed by the optical axis O of the imaging lens 12 of the camera 2 with respect to the normal line N1 of the surface 1a on the −Z side of the transparent substrate 1 is θ, and the light receiving surface 11a of the imaging element 11 of the camera 2 is An angle formed by the normal N2 with respect to the optical axis O of the imaging lens 12 of the camera 2 is defined as θ ′. 2, the distance between the imaging lens 12 and the surface 1a of the transparent substrate 1 (from the principal point of the imaging lens 12 along the optical axis O of the imaging lens 12 to the surface 1a of the transparent substrate 1). (Distance) is L, the viewing angle of the camera 2 (viewing angle in a plane parallel to the XZ plane including the optical axis O) is α, and the distance between the imaging lens 12 and the light receiving surface 11a of the imaging device 11 ( Let L ′ be the distance from the principal point of the imaging lens 12 along the optical axis O of the imaging lens 12 to the light receiving surface 11a of the imaging element 11. Furthermore, the projection magnification of the imaging lens 12 is M, and the focal length of the imaging lens 12 is f. In the example shown in FIG. 2, the center of the light receiving surface (effective light receiving region) of the image pickup device 11 is located on the optical axis O of the image pickup lens 12, but is not necessarily limited thereto. Absent.

  As can be understood from FIG. 2, the defocus amount D of the surface 1a of the transparent substrate 1 by the imaging lens 12 on the light receiving surface of the imaging device 11 for each light ray K1, K2 corresponding to the viewing angle α is the following number. It is represented by 1.

である。カメラが傾いていることによって発生するデフォーカスをＣＣＤ面の傾きで相殺するためにはデフォーカス量を考慮したレンズの公式

を満たせばよい。 On the other hand, the defocus D ′ when only the CCD surface is inclined by θ ′

It is. In order to cancel the defocus caused by tilting the camera with the tilt of the CCD surface, the lens formula considering the defocus amount

Should be satisfied.

である。これを満たすためには、

とすればよい。 Since the imaging magnification is M = L ′ / L, when L and L ′ are represented by M and f, L = (M + 1) f / M and L ′ = (M + 1) f, and using this, θ And the relationship between θ ′ and

It is. To meet this,

And it is sufficient.

  Note that the above is based on the premise that the image plane when a plane is imaged is a plane, and this is not strictly true for a large viewing angle α, but the lens focal length f is usually large with respect to the CCD size. The case is a good enough approximation.

  Therefore, the angle formed by the normal line N2 of the light receiving surface 11a of the image pickup device 11 of the camera 2 with respect to the optical axis O of the image pickup lens 12 of the camera 2 is set to θ ′ so as to satisfy θ ′ that satisfies the condition expressed by Equation 5. , The image of the surface 1a of the transparent substrate 1 obtained by the camera 2 becomes an image with a good just focus not only in the vicinity of the center of the field of view of the camera 2 but also in the peripheral part, and over the entire field of view of the camera 2 A good image with just focus is achieved.

  According to the present embodiment, since the image of the surface 1a of the transparent substrate 1 obtained by the camera 2 becomes an image having a good just focus over the entire field of view of the camera 2, as described above, While increasing the accuracy of defect detection without causing a decrease in the accuracy of defect detection, the area (collective inspection area) where defects can be detected at one time is set to the entire field of view of the camera 2 to increase the efficiency of defect detection.

  For example, a scratch with a low signal level, such as a scratch on the surface of a transparent body, can be detected with high sensitivity by combining observation in a dark field and this embodiment.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments.

  For example, the inspection object is not limited to the transparent substrate as described above, and may be an opaque substrate such as a silicon substrate. Further, the inspection object is not necessarily limited to the substrate.

  Further, the surface defect inspection apparatus according to the present embodiment is an apparatus that captures a dark field image of the surface of the inspection object, but the present invention captures a bright field image of the surface of the inspection object, and the image Even if the apparatus detects a defect on the surface of the object to be inspected based on the above, it can be applied as long as the optical axis of the imaging lens is inclined with respect to the normal line of the surface of the object to be inspected.

It is a schematic block diagram which shows typically the surface defect inspection apparatus by one embodiment of this invention. It is a schematic enlarged view which shows typically the principal part in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Camera 3 Illumination optical system 4 Processing part 11 Imaging element 12 Imaging lens

Claims (3)

An imaging unit that images the surface of the inspection object, and a processing unit that detects defects on the surface of the inspection object based on an image obtained by the imaging unit,
The imaging unit includes an imaging element that captures an image formed on a light receiving surface, and an optical system that forms an image of the surface of the inspection object on the light receiving surface,
The optical axis of the optical system is tilted with respect to the normal of the surface of the inspection object,
Compared with the case where the normal of the light receiving surface is parallel to the optical axis of the optical system, the defocus amount of the surface of the inspection object by the optical system at the periphery of the light receiving surface is reduced. Furthermore, the surface defect inspection apparatus, wherein the normal line of the light receiving surface is inclined relative to the optical axis of the optical system.   The projection magnification of the optical system is M, the focal length of the optical system is f, the angle formed by the optical axis of the optical system with respect to the normal of the surface of the inspection object is θ, 2. The surface defect inspection apparatus according to claim 1, wherein tan [theta] 'is approximately -Mtan [theta] when the angle formed by the normal line with respect to the optical axis of the optical system is [theta]'. An illumination optical system for irradiating illumination light to the surface of the inspection object;
The surface defect inspection apparatus according to claim 1, wherein the imaging unit captures a dark field image of the surface of the imaging element by the illumination light.

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