Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
1998-08-14
2001-07-03
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
C356S239200, C356S389000
Reexamination Certificate
active
06256091
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal substrate mounting platform for mounting a crystal substrate, such as a crystal blank, and a scratch inspection device for crystal substrates for detecting scratches optically by mounting a crystal substrate on a the mounting platform, and more particularly, it relates to a crystal substrate mounting platform and crystal substrate scratch inspecting device whereby the handling of crystal substrates can be simplified. Furthermore, the present invention relates to a bevelling inspection method and device for crystal substrates, and more particularly, to a bevelling inspection method and device for crystal substrates whereby real-time inspection is possible by means of image processing. Moreover, the present invention relates to an inspection method for crystal substrates, and more particularly, to a method whereby scratches and the bevelling state of crystal substrates can be inspected region by region.
2. Description of the Related Art
Crystal oscillators are fabricated from crystal blanks, but if there is even the slightest scratch in the crystal blank, then the crystal oscillator will be defective, and therefore scratch detection in crystal blanks is extremely important.
Until now, defects in crystal blanks have been inspected visually by people, by since this operation depends on human sight, it is extremely difficult to detect scratches of the order of several ten &mgr;m or less. Moreover, since this operation continues for a long period of time, the operator becomes extremely tired and consequently stable inspection results cannot be obtained, so inspection is duplicated by two or three people. Therefore, a scratch inspecting device based on image processing has been sought.
A conventional scratch inspection device based on image processing is disclosed in Japanese Unexamined Patent 7-103905, for example.
As shown in
FIG. 22
, in this device, light is shined onto an object under inspection
60
, such as a crystal blank, from three directions by providing illumination sources
61
~
63
in positions mutually separated by 90°, and CCD cameras
64
,
65
are placed between the illumination sources. These CCD cameras
64
,
65
and the illumination sources
61
~
63
are placed in positions having an angle of 45° with respect to the horizontal face of the object under inspection. To inspect scratches, one of the cameras and one of the two illumination sources on either side of this camera are turned on at the same time, and the other illumination sources and cameras are turned off. Four images are taken by the cameras
64
,
65
by implementing the four on and off combinations, thereby covering a 360° detection range. Each image is recorded in image input means
66
, and judgement processing is implemented for each of these image signals, respectively, by feature extracting means
67
and quality judging means
68
, to detect flaws, such as scratches which are independent of the direction of fracture, and the like.
However, the following problems are associated with the conventional technology described above.
1. Since the illumination and image-capturing operations are implemented obliquely using a plurality of illumination sources and cameras, equal quality in terms of focussing and light conditions setting cannot be ensured for all images, so accurate detection can be made.
2. Since the cameras are set in an oblique direction, the image becomes elliptical, so accurate dimensions and measurements cannot be obtained. In order to determine accurate dimensions and measurements, complex correctional processing is necessary.
3. Complex control is required for switching the cameras and illumination sources. Furthermore, in order to inspect one object, it is necessary to take a plurality of images, so the detection algorithm is complex and the image processing speed cannot be raised.
4. Since the cameras and illumination sources are both positioned at an angle of 45° with respect to the horizontal face, there is the risk that the background pattern of the mounting platform on which the object under inspection is mounted will be input. If the background pattern of the mounting platform is input, the SN ratio with respect to images of scratches or defects will deteriorate, thus making detection more difficult.
Therefore, in order to resolve the aforementioned problems, a scratch inspection device, whereby scattered light is shined onto the face of the object under inspection, such as a crystal blank, within an illumination angle of ±30°, from all sides of the perimeter of the object, has been investigated (Japanese Unexamined Patent 9-288063). By this means, since a dark field of view is illuminated from all sides of the perimeter of the object under inspection, and furthermore, since the illumination light is scattered light, reflected light reflected by scratches or edges is emphasized, and scratches or edges only stand out clearly in the image. Since there is no illumination at an angle greater than 30° with respect to the front or rear surface of the object under inspection, light which simply passes through the object under inspection and is reflected at the surface thereof does not form an image and therefore the image of the object under inspection as a whole forms a shadow and is not captured. The light forming an image is only the reflected light which is reflected either by scratches present in the object under inspection or the sides (edges) of the object under inspection. By image processing of this reflected light, scratches can be identified readily.
On the other hand, bevelling (chamfering) the outline (perimeter) of the crystal blank is used as a method for improving the characteristics of a crystal oscillator. In general, a cylindrical barrel system capable of high-capacity processing is used for bevelling. As illustrated in
FIG. 23
, this involves introducing a grinding material
42
into a cylindrical barrel
41
along with a plurality of crystal blanks
1
and grinding by causing the cylindrical barrel
41
to rotate. In order to improve crystal oscillator characteristics with good reproducibility, it is necessary to increase the accuracy of bevelling dimensions by means of the aforementioned method to achieve lateral and vertical symmetry.
In the aforementioned cylindrical barrel system, the bevelling state varies depending on the number of crystal substrates introduced into the barrel, the type of grinding material, the speed of revolution, and the like, and even if these conditions are kept uniform, this does not necessarily mean that the same bevelling state will always be achieved. Crystal substrate manufacturers rely on their own know-how to a large degree, but since this know-how is a variable factor, it cannot be regarded as an ideal approach, and currently uniform accuracy in bevelling dimensions cannot be maintained at all times and unexpected factors also arise. In order to improve accuracy in bevelling dimensions, a bevelling inspection method is required, which is capable of evaluating the state of bevelling of the crystal substrate surfaces, and feeding these results back to the bevelling process.
Since the bevelling process is achieved by applying extremely small scratches, a standard light field illumination method will not produce any significant difference between bevelled and unbevelled sections, so the bevelling state of the crystal substrate surfaces cannot be inspected by means of visual inspection by an operator, or by an image processing technique. Therefore, conventional inspection of bevelling has relied unavoidably on physical methods, such as (1) bevel measurement or (2) projection.
(1) Bevel measurement method
This method uses a laser height measuring device, and involves vapour deposition of reflective silver film onto the rear face of the crystal blank, whereupon a laser light source is shined onto the surface of the crystal blank and swept (scanned) in a diametrical direction (linear direction), and the level on straight lines is
Font Frank G.
Nippon Maxis Co., Ltd.
Oliff & Berridg,e PLC
Ratliff Reginald A.
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