JPH02264848A - Inspection of optical disk recording medium - Google Patents

Abstract

PURPOSE:To improve yield by performing subtraction processing at every mutually corresponding pixels between the second image signal and the image signal carrying a mask image due to the first image signal and detecting a flaw on the basis of the difference signal. CONSTITUTION:Illumination light 13 is emitted from a light source 11 to illuminate an optical disk 10 so as to form an angle of about 45 deg. within the plane vertical to the surface of the disk with respect to the tangential direction of a group 11c. The part of this disk 10 is imaged by a television camera 15 and an image signal S1 is inputted to an image processor 16. Next, the signal S1 is subjected to binarization processing in the processor 16 and an image signal S1' is inputted to an image display means 17. When foreign matter is present on the surface of the substrate of the optical disk 10, illumination light 13 is scattered and the part of the foreign matter is imaged as a specifically bright part. When the threshold value of binarization processing is set appropriately, the bright image showing the foreign matter is displayed on the means 17 and the size of the image thereof, that is, the size of the foreign matter can be discriminated by utilizing the scale in the means 17.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method for inspecting defects in an optical disc, and more specifically, to inspecting defects on the surface of a substrate and defects on the surface of a recording layer formed on the substrate. The present invention relates to an inspection method for an optical disc recording medium that can distinguish and detect.

(Prior Art) A read-only optical disk on which various information is recorded has bit strings carrying control information such as address information and recording information arranged so as to extend concentrically or spirally. In addition, even in write-once optical disks and erasable/rewritable optical disks (herein referred to broadly as optical disks, including magneto-optical disks), there are also pits and guides that carry control information such as the address information. Groups are provided and they are arranged as described above.

As a method for inspecting defects in various optical disc recording media as described above, for example, as shown in Japanese Patent Laid-Open No. 59-9546, the recording medium is irradiated with light and optical tracks such as the above-mentioned bit strings and groups are detected. A method is known in which this light diffracted by a laser beam is detected and defects are inspected based on the detection results. On the other hand, as shown in Japanese Patent Application Laid-Open No. 61-214248, for example, the speed of defect inspection can be increased by capturing a two-dimensional image of a recording medium and performing defect inspection based on the image signal obtained thereby. Methods aiming at this are also known.

(Problem to be Solved by the Invention) In an optical disc recording medium, a recording layer is formed on a transparent substrate such as PC (polycarbonate), and defects occur on the exposed surface of this substrate (the surface opposite to the recording layer). There are two main types: those that occur on the surface of the recording layer (the surface in contact with the substrate) and those that occur on the surface of the recording layer (the surface in contact with the substrate).

Compared to the latter, the former of these 2P4i-type defects is
If the size is about the same, there is a low probability that it will be fatal to the use of the optical disc. In other words, the recording beam for recording signals on an optical disk recording medium and the reading beam for reading signals from the optical disk recording medium have a relatively large beam diameter when passing through the surface portion of the substrate, and become distorted as they pass through the substrate. This is because the image of a defect on the substrate surface becomes significantly smaller on the recording layer because it reaches the recording layer after reaching the recording layer. Considering this point, the above two types of defects should be clearly distinguished and detected, and a relatively large defect judgment threshold value should be set for defects on the substrate surface, and a relatively small defect judgment threshold should be set for defects on the surface of the recording layer. It is preferable to set a defective determination threshold value for each type of defect, and to determine that the recording medium is defective when the size of each type of defect exceeds the respective threshold value.

However, with conventional defect inspection methods, it has been impossible to distinguish and detect the above two types of defects. For this reason, conventionally, a relatively small value that takes into account defects on the surface of the recording layer has been uniformly adopted as the above-mentioned defect determination threshold. However, if this is done, defects on the surface of the substrate that are not large enough to be fatal will of course be used as the basis for determining the defect, which will lead to so-called over-inspection, which will make the defect inspection unnecessarily strict.

Therefore, it is an object of the present invention to provide an optical disc recording medium inspection method that can distinguish and detect the above two types of defects.

(Means and Effects for Solving the Problems) As described above, in the method for inspecting an optical disk recording medium according to the present invention, a recording layer is formed on a transparent substrate, and a recording layer is formed on the recording layer in a concentric or spiral manner. In a method for inspecting defects in an optical disc recording medium provided with optical tracks,
irradiating the recording medium with first illumination light from the surface side of the substrate opposite to the recording layer installation side from a direction forming an angle in a plane perpendicular to the recording medium surface with respect to the track tangential direction; A first image signal is obtained by imaging the portion of the recording medium irradiated with light by an imaging means, and a defect on the substrate surface is detected based on the first image signal, and a defect on the substrate surface opposite to the recording layer installation side is detected. A second illumination light is irradiated onto the recording medium from the surface side of the disc from a direction forming an angle in a plane perpendicular to the surface of the recording medium with respect to the radial direction of the disk, and a diffraction image due to the irradiation of the second illumination light is captured by an imaging means. to obtain a second image signal, and one point on the substrate surface in the image based on the first image signal is a second image signal.
converting the image so that it coincides with the projection point of the illumination light onto the surface of the recording layer, and combining this converted image with the image based on the first image signal to form a mask image; A subtraction process is performed for each corresponding pixel between the image signal of the mask image and the image signal that carries the mask image, and defects on the surface of the recording layer are detected based on the difference signal. be.

(Example) Hereinafter, the present invention will be described in detail based on an example shown in the drawings.

FIG. 1 shows an apparatus for inspecting optical disc recording media for defects using the method of the present invention.

The recording medium in this example is a write-once optical disc 10. As shown in detail in FIG. 2, this optical disc 10 has a recording layer 10 made of a reflective film etc. on a substrate 10a of the PC or the like.
b is formed, and a large number of guiding groups IOc extending concentrically, for example, are formed on this recording layer 10b. At the time of defect inspection, the optical disc 10 is placed in such a state that the substrate 10a is located on the upper side in FIG.

This optical disc 10 is first provided with a first light source 11 and a first light source 11.
illumination light 13 is emitted. As this light source 11, for example, a strobe illumination lamp such as a xenon lamp is used. Further, this first illumination light 13 is transmitted to the group I (l
It is irradiated from a direction forming an angle of, for example, about 45'' in a plane perpendicular to the disk surface with respect to the tangential direction of c.The part of the optical disk IO that is irradiated with this first illumination light 13 is illuminated by a CCD camera, etc. The image is taken by a television camera 15. This television camera 15 has, for example, about 400,000 pixels, and images an area 10d of approximately 1010×8 on the optical disk IO.

An image signal (video signal) Sl output from the television camera 15 is input to an image processing device 16.

This image processing device 1G detects defects on the surface of the substrate LOa based on the image signal S1. The procedure for this process will be explained below. The image processing device 16 has a built-in A/D converter and image memory, binarizes the digitized image signal S1, and manually outputs the processed image signal Sl' to an image display means 7 such as a CRT. . As shown in Figure 2,
If foreign matter A exists on the surface of the substrate 10a of the optical disc 10, the first illumination light 13 will be scattered at that portion. In other words, this part of the foreign object A is imaged as a part that is uniquely brighter than the surrounding parts. Therefore, if the threshold value of the binarization process described above is set appropriately, the fourth
As shown in FIG. 1, an image in which a bright (e.g., white) image Pa representing the foreign substance A exists in a dark (e.g., black) background H is displayed on the image display means 17. Become. The size of this image Pa, that is, the size of the foreign object A, is
For example, it can be determined using the scale displayed in the image display means 17, or it can be automatically determined by incorporating a known quadrature algorithm into the image processing device 16. Regarding substrate surface defects caused by foreign particles, a relatively large threshold size, for example, equivalent to a diameter of 500 μm, is set, and if a substrate surface defect with a size exceeding this threshold exists, the optical disc 10 is The product is determined to be defective.

The image processing device 1G stores the image signal Sl' carrying the binary image described above in an internal memory for inspection of recording layer surface defects, which will be described later.

As shown in FIG. 2, in the optical disc 1O, foreign matter C may be present on the surface of the recording layer 10b, resulting in a defect. Detection of this foreign substance C will be explained below. When detecting this defect, the first light ill is turned off, a separate second light source 12 is turned on, and the second illumination light 14 is irradiated onto the optical disc 10. This second light source 1
2 is also similar to the first light source 11 described above. This second illumination light (4) is irradiated from a direction that is perpendicular to the disk surface and forms an angle of, for example, about 45'' with respect to the radial direction of the optical disc 10. The illumination light 14 is diffracted by the groups LOc arranged regularly at regular intervals, and the diffraction image thereof is captured by the television camera 15.

At this time, the image signal S2 outputted by the television camera 15 is also
The image is input to the image processing device 16 described above. Since the above-mentioned diffraction image has large illuminance unevenness, in this case, in order to detect the defective portion, its outline portion is extracted. That is, the image processing device 16 performs differential processing etc. on the image signal S2,
Extracts the portion of the diffraction image where the density change is significantly large. Next, the image processing device 1B performs binarization processing on the differentially processed image signal based on a predetermined threshold value to obtain an image signal S20. The above diffraction image shows foreign matter A on the surface of the substrate 10a and foreign matter C on the surface of the recording layer 10b shown in FIG.
In addition, projection B of the foreign matter A onto the surface of the recording layer 10b
will be shown. Therefore, if the above differential processing and 2
If an image is displayed on the image display means 17 based on the image signal S2° after the value processing, each outline EB of the foreign object A1 projection B and foreign object C will be displayed as shown in FIG.
, Ebb and EC will be shown. Note that this contour extracted image signal S2o may be subjected to contour enhancement processing as appropriate. The image processing device 1G receives the image signal S2. is stored in the -tan's internal memory.

The image signal S2 changes along a line passing through the projection B of the foreign object A1 and the projection B of the foreign object C, as shown in FIG. As shown in the figure, this image signal S2 has a high level (
In addition to a high-brightness portion Sa, a low-level portion Sc that is responsible for the foreign matter C on the surface of the recording layer 10b, and a low-level portion sb that is responsible for the projection B. If this low level portion sb does not occur, the substrate 108 can be
Although foreign matter A on the surface and foreign matter C on the surface of the recording layer 10b can be detected separately, in reality, as described above, it is impossible to distinguish them by such threshold processing.

Next, the image processing device 16 processes the image signal Sl' stored in the internal memory.
A conversion process is performed to match one point on the image (shown in FIG. 4 (1)) with the point projected onto the surface of the recording layer 10b by the second illumination light (4). If the image is reproduced based on the image signal S1'' after this conversion process, if the image Pa as described above exists in the image shown in FIG. (See Figure 2) and the transformed image Pa' shown in Figure 4 (2).
Then, the contour Eb of projection B in the image of Fig. 4 (4)
The positions will be aligned. Note that the above movement amount ΔL is determined by θ being the irradiation angle of the second illumination light 14 with respect to the surface of the substrate 10a, and dln being the thickness and refractive index of the substrate 10a, respectively.
When , you can write .

Next, the image processing device 16 processes the image signals Sl' and 81
As shown in FIG. 4 (3), an image signal Slo is generated which carries an image in which both images Pa and Pa' are shown. In this case, the images Pa and Pa' are It is preferable to perform an expansion process.

Next, the image processing device 16 processes the image signal S2. and the image signal S18, a subtraction process of 5 sub -82o -51 degrees is performed for each corresponding pixel. The difference signal S s obtained in this way
ub is input to the image display means 17 and is provided for image display. The image thus displayed is, as shown in FIG. 4 (5), in which the contours Ea and Eb shown in FIG. becomes. Therefore, in this case as well, the size of the defect on the surface of the recording layer 10b can be detected in the same manner as the size detection of the defect on the back surface of the substrate 1 (la) described above.
A relatively small threshold value equivalent to 0 μm is set, and if there is a recording layer surface defect with a size exceeding this threshold value, the optical disc IO is determined to be a defective product.

(Effects of the Invention) As described above in detail, in the optical disc recording medium inspection method of the present invention, substrate surface defects and recording layer surface defects of an optical disc recording medium can be clearly distinguished and detected. Therefore, according to this method, it is possible to set the optimal defect judgment threshold for each of the above two types of defects and judge the recording medium as defective, thereby suppressing the above-mentioned over-detection and Manufacturing yield can be improved.

Furthermore, according to the method of the present invention, since the two types of defects described above can be detected separately, it is possible to improve the accuracy of analysis when analyzing the cause of defect occurrence.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing an example of an apparatus for carrying out the method of the present invention, FIG. 2 is a schematic diagram showing the cross-sectional shape and defect state of an optical disk according to the present invention, and FIG. 3 is a diagram showing one step of the method of the present invention. Graph 1 showing changes in the obtained image signal and FIG. 4 are explanatory diagrams illustrating an image based on the image signal obtained in each step of the method of the present invention. 10... Optical disk 10a... Substrate 10b.
...Recording layer 10c...Group 11...First light source 12...Second light source 13...First illumination light 14...Second illumination light! 5... Television camera 16... Image processing device 17... Image display means Fig. 1 Fig. 4 (+) Fig. 3

Claims (1)

[Scope of Claims] A method for inspecting defects in an optical disc recording medium, in which a recording layer is formed on a transparent substrate, and optical tracks extending concentrically or spirally are provided on the recording layer, comprising: irradiating the recording medium with a first illumination light from a direction forming an angle in a plane perpendicular to the recording medium surface with respect to the track tangential direction from the surface side of the substrate opposite to the recording layer installation side; A portion of the recording medium irradiated with the illumination light is imaged by an imaging means to obtain a first image signal, a defect on the surface of the substrate is detected based on the first image signal, and a defect on the surface of the substrate is detected; A second illumination light is irradiated onto the recording medium from the surface side opposite to the installation side from a direction forming an angle in a plane perpendicular to the recording medium surface with respect to the disk radial direction, and by this second illumination light irradiation. A second image signal is obtained by capturing a diffraction image with an imaging means, and one point on the substrate surface in the image based on the first image signal is recorded by the second illumination light. converting the image so that it coincides with the projection point on the layer surface, combining this converted image with an image based on the first image signal to form a mask image, and combining the second image signal and this mask image. 1. A method for inspecting an optical disk recording medium, comprising performing subtraction processing for each corresponding pixel with an image signal, and detecting defects on the surface of the recording layer based on the difference signal.