JPS61211876A - Device for estimating optical disk defect - Google Patents

Abstract

PURPOSE:To correctly estimate a quality of an optical disk and investigate causes producing defect of it by obtaining a position data of a start end and a final end of the defect by using an address as position reference. CONSTITUTION:From an optical head 3, a reading signal (a) composing of respective address signal and a defect signal representing a defect is obtained, amplified, thereafter supplied to a code processing circuit 5, a servo circuit 6 and a defect detecting circuit 8. The code processing circuit 5 extracts a track address signal and a sector address signal from the reading signal (a) by using a synchronous signal (a) as time reference and supplies to a memory circuit 9 as a reference position data (b). The servo circuit 6 carries out a focus control or a tracking control of the optical head 3. In the defect detecting circuit 5, at first, the synchronous signal is separated from the reading signal (a) the respective address signal is removed to have a signal of only the defect signal. Then, a start end position and a final end position of the defect signal are detected, and a data indicating the start end position of the defect signal and a data indicating the final end position of the defect signal are formed by using the synchronous signal as position reference.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc defect evaluation device that can obtain data necessary for evaluating the quality of write-once optical discs, searching for the cause of defects, and the like.

[Prior art]

When producing optical discs, physical defects such as scratches on the recording layer and contamination of impurities cannot be avoided. If such a defect exists on the surface of an optical disk, when an information signal is written to or read from the optical disk, the defect causes a dropout in the read information signal. In the case of optical discs on which digital data is written and read, such as optical discs used as external memory for computers, if a defect occurs in the read digital data, this can cause code errors in the digital data. I'll wake you up.

Such code errors can be removed to a greater extent by signal processing by adding an error correction detection code to the digital data. However, there is a limit to the code error correction ability, and if the optical disc has many defects, code errors in read digital data cannot be completely corrected.

Therefore, it is necessary to evaluate the quality of the optical disc, and it is also necessary to investigate the causes of defects in the optical disc and to improve the quality of the optical disc by returning the results to the production process and the like. For this purpose, it is first necessary to obtain data regarding defects in the optical disc.

Incidentally, apparatuses for inspecting wafers for defects in the production process of transistors, etc., are conventionally known. The inspection equipment optically scans the surface of the wafer to detect defects.
It is designed to obtain data such as the number and distribution of defects. It is conceivable that such a method could also be used for optical discs to detect various data regarding defects existing on their surfaces.

[Problem that the invention seeks to solve]

However, the conventional defect detection device described above has a problem with the number of defects (
For example, it is possible to know the total number of defects on the entire surface, the average number of defects per unit area), the distribution of defects, etc., but it is not possible to know specifically where and what kind of defects are present on the wear. Therefore, if the method of such a defect detection device is applied by engraving an optical disc, only data of the same level of content can be obtained, and it is only enough to determine whether the optical disc is good or bad.

In the case of an optical disc, even if there are defects that exceed the code error correction capability of signal processing, it can still be used as long as the number of defects is not extremely large. For example, digital data can be written while avoiding defective parts.

However, when applying the defect detection device method described above to evaluate the quality of optical discs, it is only possible to determine whether the optical disc is good or bad, and optical discs that are determined to be of low quality cannot be used even if the method described above is used. Even if the optical disc is of good quality, it will be treated as unusable, and it is extremely embarrassing to set standards for determining whether an optical disc is good or bad.

In addition, in order to feed back data on optical disc defects to the production process and further improve its quality, it is necessary to know the nature of the defects, such as their shape, size, and location, and to investigate their causes. There is. However, the above-mentioned defect inspection device does not provide data regarding such defects themselves, and therefore, even if the method of this defect inspection device is applied to defect inspection of optical disks,
It is not possible to obtain data useful for improving its quality.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk defect evaluation apparatus that solves these problems and can obtain specific data such as the shape, size, and location of defects occurring on an optical disk.

[Means for solving problems]

To this end, the present invention focuses on the fact that an address is stored in advance for each block in a write-once optical disc, and uses the address as a position reference to obtain position data of the start and end of a defect. This is how it was done.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of an optical disk defect evaluation apparatus according to the present invention, in which 1 is an optical disk, 2 is a rotary drive motor, 3 is an optical head, 4 is an amplifier, 5 is a code processing circuit, and 6 1 is a servo circuit, 7 is a reading system, 8 is a defect detection circuit, 9 is a memory circuit, 10 is a display processing circuit, 1) is an output device, and 12 is a control circuit.

In the figure, the reading system 7 is controlled by a control circuit 12, the rotational drive motor 2 is drive-controlled to rotate the optical disc 1 to be evaluated, and the optical head 3 is driven in the radial direction of the optical disc 1 to rotate the optical disc 1. scan. A synchronizing signal, an address representing the track (i.e., track address), and an address representing the sector (i.e., sector address) are stored in advance in the optical disc 1 for each sector of each track, and the control circuit 12 The scanning position of the optical head 3 at each moment is constantly monitored using these track addresses and sector addresses. That is, the control circuit 12
A track address and a sector address are sequentially specified, and the rotation of the rotary drive motor 2 and the optical The position of the target head 3 is controlled.

The optical head 3 sequentially scans the optical disk 1 from the outermost track or from the innermost track.

Possible defects in the optical disc 1 include scratches, dents and protrusions in the recording layer due to the inclusion of impurities, and adhesion of dust. If there are no such defects, the recording layer has a smooth surface (not a flat surface because of the guide grooves) except for the portion where each address is written, and the optical head 3 can move the optical disc 1. The intensity of the laser light reflected and detected from this part of the laser light irradiated to the area is constant. However, since diffuse reflection of the laser beam occurs in the defective area, the intensity of the detected reflected laser beam is different from the intensity of the laser beam detected by being reflected from the surface of the recording layer that has no defects. Become.

Therefore, the optical head 3 outputs a read signal a consisting of each address signal and a defect signal representing such a defect.
is obtained, and after being amplified by the amplifier 4, the code processing circuit 5.
The signal is supplied to a servo circuit 6 and a defect detection circuit 8.

The code processing circuit 5 extracts a track address signal and a sector address signal from the read signal a, using the synchronization signal as a time reference, and supplies them to the memory circuit 9 as reference position data b. Similarly, the servo 15J path 6 extracts a track address signal and a sector address signal, and uses them to perform focus control and tracking control of the optical head 3.

In the defect detection circuit 5, first, the synchronization signal is separated from the read signal a, and each address signal is removed to make a signal containing only the defect signal.Then, the start and end positions of the defect signal are detected, and this synchronization signal is detected. Data representing the start position of a defect signal using the signal as a position reference (hereinafter referred to as defect start position data)
and data representing the end position of the defect signal (hereinafter referred to as defect end position data). Note that a pair of defect start position data and defect end position data for the same defect signal is hereinafter referred to as defect position data.

When the defect position data C is formed in the defect detection circuit 8, this and the reference position data b from the code processing circuit 5 are written as a pair to an address designated by the control circuit 12 of the memory circuit 9. At this time, a code error may occur in the reference position data b due to a defect. Therefore, when writing the defect position data C and the reference position data b to the memory circuit 9, the control circuit 12 also sends the reference position data d consisting of a track address signal and a sector address signal to the memory circuit 9, and It is compared with the position data b, and when the two match, only the reference position data b is written into the memory circuit 9, and when the two do not match, the reference position data d from the control circuit 12 is also written into the memory circuit along with the reference position data b. Write it to 9.

Note that FIG. 2 shows the arrangement of each data written in the memory circuit 9 when there is a code error due to a defect in the reference position data b.

Such operation is performed for each defect signal. Even when there are multiple defects in the same block, a pair of reference position data is created for each defect position data for each defect. Therefore, defect position data in the same sector is paired with reference position data having the same content.

When the optical head 3 finishes scanning all the tracks on the optical disk 1, the memory circuit 9 stores defect position data for all defects on the optical disk 1 together with reference position data. These data are the starting points of defects on the optical disc 1.

It represents the absolute position of the end, and after reading this data and processing it in the processing circuit 10, it is output to an output device 1) such as a CRT display, an X-Y plotter, or a printer, so that the quality of the optical disc 1 can be evaluated. It can be used as a material for investigating the causes of defects and defects.

Next, materials obtained from the data stored in the memory circuit 9 will be explained here.

(1) Reference position data stored in the memory circuit 9 (when the reference position data b from the code processing circuit 5 and the reference position data d of the control circuit 12 correspond to the same defect position data, The total number of defects existing on the disk 1 can be known by reading out and counting either one of the defect start position data and the defect end position data.

(2) The number of defects in each sector can be known by performing a count similar to that in (1) above for each sector of each track and detecting the number of defects in each sector.

The data obtained above are expressed as numerical values, but it goes without saying that these can also be used as data for evaluating the quality of optical discs.

(3) By performing subtraction processing between the defect start position data and the defect end position data of the same defect position data, data on the length of the defect along the track is obtained, and the defect By obtaining length data and displaying a similar two-dimensional pattern on the optical disc 1 using the output device W1) based on this data, it is possible to display the defect pattern within this predetermined area. Therefore, it is possible to know the specific two-dimensional shape and size of the defect from this information, which serves as data for investigating the cause of the defect.

(4) Divide the optical disc 1 in the circumferential direction and radial direction, define the divided areas as blocks, distribute defect position data to each block based on the reference position data, and further determine the size of the defect from the defect position data. The defect rate for each block (ratio of the total area occupied by defects in the block to the total area of the recording area of the optical disc 1) is determined by calculating the defect rate, and based on this data, the output device 1) compares the defect rate to the optical disc 1. By displaying a clear secondary pattern, the defect distribution on the optical disc 1 can be known.

FIG. 3 shows the surface of the optical disc 1 divided into 64 parts in the circumferential direction.
The optical disc 1 is divided into 21 blocks in the radial direction and consists of 1344 blocks, and an example of the defect distribution on the optical disc 1 is shown by displaying the difference in the defect rate for each block. In the figure, the magnitude of the defect rate of a block is expressed by the density of hatching.

By reading out all the data stored in the memory circuit 9 and printing it out as is, the absolute position of the defect on the optical disc 1 can be known. When directly observing defects in a product using a microscope, the position of the defect can be known, which saves the effort of finding the defect.

(6) Sectors with defects can be extracted.

This means that when the optical disc 1 is actually used, it is possible to specify a sector in which a defect exists regarding this optical disc 1, and therefore, writing of digital data to this specified sector can be prohibited. . As a result, digital data can be easily written while avoiding at least sectors with defects that make code correction impossible, and the reliability of the optical disc is improved.

Although examples of materials based on data stored in the memory circuit 9 have been shown above, it goes without saying that the data is not limited to these and that such data can be used as desired.

FIG. 4 is a block diagram showing a specific example of the defect detection circuit 8 in FIG. 1, in which 13 to 16 are input terminals, 17 is a counter, 18 and 19 are latch circuits, 20 is a comparator, 21 is an inverter, 22 is a reference voltage source.

The operation of this specific example will be explained below using the timing chart of FIG.

From the control circuit 12 (Fig. 1), the input terminal 13
The clock CK is supplied via the input terminal 16.
through the reference voltage V. is supplied to converter 20.

Note that, for convenience, this reference voltage V.

A reference voltage source 22 is shown as a generation source. Furthermore, the read signal a supplied from the input terminal 15 is the defect signal N
As explained earlier in Figure 1,
The read signal a from the amplifier 4 is obtained by removing the synchronization signal, track address signal, and sector address signal.

Furthermore, this synchronization signal is supplied from the input terminal 14 to the counter 17 as a reset pulse R5.

Therefore, the counter 17 counts the clock CK, but at every reset pulse (therefore, the counter 17 counts the clock CK)
It outputs a count value A which is reset for each sector in FIG. This count value A is supplied to latch circuits 18 and 19.

On the other hand, in the comparator 20, the read signal a and the reference voltage ■
. A latch pulse R1 representing a defect signal N is generated. Here, the defect signal N is the read signal a
shall reduce the level of the reference voltage■. Since the level of the read signal a is set lower than the level of the part of the read signal a that is not a defective signal, the latch pulse R8 becomes a low level, and its falling edge represents the beginning of the defective signal N, and its rising edge similarly represents the end. ing. This latch pulse R8 is supplied to the latch circuit 18 as it is, and is also inverted by the inverter 21 and supplied to the latch circuit 19.

The latch circuits 18 and 19 perform a latching operation at the falling edge of the supplied latch pulse. Therefore, deceptive circuit 1
8 latches the count value A of the counter 17 at the falling edge of the latch pulse R8. Assuming that the count value A at this time is A1, the latch circuit 18 latches the digital value A1, treats it as the previous defect start position data D, and outputs it to the memory circuit 9 (see Figure 1). RIl rises, so the latch pulse Ra obtained from the inverter 2I falls, and the latch circuit 19 latches the count value A of the counter 17 at the falling edge.

If the count value A at this time is A2, then the latch circuit 1
9 latches the digital value A and outputs it to the memory circuit 9 as the previous defect end position data D8.

In this way, defect position data C is obtained.

In the second specific example, the reference voltage ■. This is a case in which the value is constant, but it may be made variable. This is the reference voltage V after the entire scanning of the optical disk 1 (FIG. 1) is completed and the data obtained at that time is written in the memory circuit 9. The optical disk 1 is scanned again by changing the value, and defect position data is obtained and written into the memory circuit 9 in the same manner as described above.

That is, the entire optical disc 1 is scanned multiple times, and the reference voltage V is set for each entire scan. This is to obtain defect position data by making the values different. The defect position data for each overall scan thus obtained represents the starting and ending positions of the defect at the depth of the recording layer of the optical disc 1.

Therefore, if a partial two-dimensional pattern of the optical disc 1 is displayed using the defect position data obtained for each overall scan, it is possible to know the shape of the defect at each depth of the recording layer of the optical disc 1. Using all of the obtained defect position data, a partial two-dimensional pattern of the optical disc 1 is displayed in different colors or densities for the defective parts based on the defect data for each overall scan, as shown in FIG. , defects can be displayed three-dimensionally. Therefore, it is possible to know not only the planar shape and size of the defect, but also the three-dimensional structure of the defect, and the nature of the defect.

This will be important material in investigating the cause of the outbreak. In addition, the 6th
In the figure, the hatched area represents a defect, and the depth of the hatch represents a difference in the depth of the defect.

In the specific example shown in FIG. 4, it is assumed that the defect signal N lowers the rail of the read signal a;
If there is also a defect that increases the health, another comparator is provided in FIG. ■ Reference voltage at a different level. ′ (
However, such a defect can be detected by comparing the level of the base Y# voltage Vo' (set higher than the level of the non-defective part of the read signal a), and this can be used as a latch pulse to similarly operate the latch circuit. It is sufficient to supply the data on 18.19.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain data specifically representing not only the number and distribution of defects on an optical disk, but also the nature of the defects themselves such as shape and size, and the location of the defects. Therefore, an excellent effect can be obtained in that it becomes possible to accurately evaluate the quality of an optical disc and investigate the causes of defects.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disk defect evaluation device according to the present invention, FIG. 2 is a schematic diagram showing an example of data written to the memory circuit of FIG. 1, and FIG. FIG. 4 is a block diagram showing an example of the defect detection circuit in FIG. 1, FIG. 5 is a timing chart for explaining the operation of this specific example, and FIG. FIG. 3 is a pattern diagram showing a three-dimensional display of defects on an optical disc according to an example. 1... Optical disk, 3... Optical head, 5...
Code processing circuit, 8... Defect detection circuit, 9... Memory circuit, 10... Processing circuit, 1)... Output device, I2
... Control circuit, 17... Counter, 18.
19...Latch circuit, 20...Converter. Agent Patent Attorney Take Junshi Department (1) or 1 Gain J 1st [D,,”7 Figure 2 I4 Zero 1) Odd 50 Zerai Mei Figure 3 ○ Figure 6

Claims (3)

[Claims] (1) In a defect evaluation device for an optical disk in which a synchronization signal and an address are written in advance for each sector of each track, an optical head that sequentially reproduces and scans the tracks on the optical disk, and a a code processing circuit that extracts an address signal representing the address of the sector from the read signal and generates reference position data for each sector; and a code processing circuit that extracts only a defect signal from the read signal and generates the reference position data for each defect signal. A defect detection circuit that generates defect position data based on a data pair of defect start position data and defect end position data in the sector, and a data pair that combines the defect position data and the corresponding reference position data. a processing circuit that reads a desired data pair from the memory circuit and generates a signal for display; and an output device that is supplied with the signal from the processing circuit and displays data regarding the defect. An optical disc defect evaluation device characterized by: (2) In claim (1), the defect detection circuit includes a counter that counts a clock of a constant period and is reset for each synchronization signal of the read signal, and a counter that controls the read signal and the reference voltage to a level. a comparator that compares and generates a pulse representing the period of the defective signal; a first latch circuit that latches the count value of the counter at the beginning of the pulse; and a first latch circuit that latches the count value of the counter at the end of the pulse. and a second latch circuit, wherein the output digital value of the first latch circuit is used as the defect start position data, and the output digital value of the second latch circuit is used as the defect end position data. Optical disk defect evaluation device. (3) The optical disk defect evaluation apparatus according to claim (2), wherein the level of the reference voltage is made variable.