JPH079713B2 - Optical disk defect evaluation system - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical disk defect evaluation apparatus capable of obtaining data necessary for quality evaluation of a write-once optical disk, search for a cause of a defect, and the like. .

[Prior art]

When producing an optical disk, physical defects due to flaws in the recording layer, mixing of impurities, etc. cannot be avoided. If such a defect is present on the surface of the optical disk, when the information signal is written in and read from the optical disk, the information signal read out due to the defect is missing. In the case of an optical disk that writes and reads digital data, such as an optical disk used as an external memory of a computer, if a defect occurs in the read digital data, this causes a digital code error. Will be caused.

Such code error can be removed to some extent by signal processing by adding an error correction detection code to digital data. However, the code error correction capability is also limited, and when the optical disk has many defects, the code error correction of the read digital data cannot be performed completely.

Therefore, it is necessary to evaluate the quality of the optical disk, and to investigate the cause of the defect of the optical disk and reduce it to the production process to improve the quality of the optical disk. For this purpose, it is first necessary to obtain data on the defects of the optical disk.

By the way, conventionally, an apparatus for inspecting a wafer for defects in a transistor manufacturing process or the like is known. The inspecting device is configured to optically scan the surface of a wafer to detect defects and obtain data such as the number and distribution of defects. It is conceivable to detect various data of defects existing on the surface of an optical disk by using such a method.

[Problems to be solved by the invention]

However, the above-mentioned conventional defect detection device can know the number of defects (for example, the total number of defects on the entire surface, the average number of defects per unit area), the distribution of defects, etc. It is not possible to know concretely whether there is any defect. Therefore, when the method of such a defect detection device is applied to an optical disk, only data having the same content can be obtained, and the quality of the optical disk can be determined.

In the case of an optical disk, even if there are defects beyond the code error correction capability by signal processing, if they are extremely few, they can be used. For example, the digital data may be written while avoiding the defective portion.
However, if the quality evaluation of the optical disk is performed by applying the above method of the defect detection device, only the quality of the optical disk can be determined, and the optical disk determined to have the low quality is used as described above. Even if it is possible, it will be treated as unusable, and it is very difficult to set a criterion for judging the quality of the optical disk.

Further, in order to reduce the data on the defects of the optical disk to the production process and further improve the quality thereof, it is necessary to know the properties of the defects such as the shape, size, and generation position of the defects and to investigate the cause thereof. is there. However, the above-mentioned defect inspection apparatus does not provide data on such a defect itself. Therefore, even if the method of this defect inspection apparatus is applied to the defect inspection of the optical disk, the data useful for improving the quality thereof is not obtained. Can't get

An object of the present invention is to solve the above problems and provide an optical disk defect evaluation apparatus capable of obtaining specific data such as the shape, size, and generation position of a defect occurring in an optical disk. .

[Means for solving problems]

For this reason, the present invention pays attention to the fact that the write-once type optical disk stores an address for each block in advance, and based on the address, the position data of the beginning and the end of the defect are stored. It's something I got to get.

〔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. , 6 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, 11 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 rotation drive motor 2 is driven and controlled, and the optical disk 1 to be evaluated rotates, and the optical head 3 moves in the radial direction of the optical disk 1. Driven to scan it. The optical disk 1 stores a synchronization signal, an address representing a track (that is, a track address) and an address representing a sector (that is, a sector address) for each sector of each track, and the control circuit 12 , The track address and sector address are constantly used to monitor the instantaneous scanning position of the optical head 3. That is, the control circuit 12 sequentially designates the track address and the sector address, and rotationally drives so that the scanning position by the optical head 3 coincides with the sector of the designated sector address on the track of the designated track address. The rotation of the motor 2 and the position of the optical point head 3 are controlled.

The optical head 3 sequentially scans the optical disk 1 from the outermost track or the innermost track. Light disk 1
Defects in the recording layer may include dents, protrusions, dust, etc. on the recording layer due to flaws, impurities, and the like.
If there is no such defect, the recording layer has a smooth surface (not a flat surface due to the guide groove) except for the portion where each address is written, and the optical disk 3 is provided with an optical disk. The intensity of the laser light reflected and detected from this portion of the laser light radiated to 1 is constant.
However, since the irregular reflection of the laser light occurs at the defect portion, the intensity of the reflected laser light detected differs from the intensity of the laser light reflected and detected from the surface of the recording layer having no defect. Become.

Therefore, the read signal a from the optical head 3 is composed of the respective address signals and the defect signal representing the defect.
Is obtained, amplified by the amplifier 4, and then supplied to the code processing circuit 5, the servo circuit 6 and the defect detection circuit 8.

The code processing circuit 5 extracts the track address signal and the sector address signal from the read signal a with the synchronization signal as a time reference, and supplies them to the memory circuit 9 as reference position data b. Further, the servo circuit 6 similarly extracts the track address signal and the 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, only the defect signal is removed by excluding each address signal, and then the start position and the end position of the defect signal are detected and the synchronization signal is detected. Data representing the start position of the defect signal with 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). The 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, the defect position data c and the reference position data b from the code processing circuit 5 are paired and written at an address designated by the control circuit 12 of the memory circuit 9. Be done. At this time, a code error may occur in the reference position data b due to the defect. Therefore, when the defect position data c and the reference position data b are written in the memory circuit 9, the control circuit 12 also sends the reference position data d including the track address signal and the sector address signal to the memory circuit 9, and the reference position data b When both match, the reference position data b is written in the memory circuit 9. When both do not match, the control circuit together with the reference position data b is written.
The reference position data d from 12 is also written in the memory circuit 9. Note that FIG. 2 shows the arrangement of each data written in the memory circuit 9 when the reference position data b has a code error due to a defect.

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

When the scanning of all tracks of the optical disk 1 by the optical head 3 is completed, the defect position data for all the defects of the optical disk 1 are stored in the memory circuit 9 together with the reference position data. These data represent the absolute positions of the start and end of the defect on the optical disk 1,
After reading these data and processing them in the processing circuit 10,
By outputting to an output device 11 such as a CRT display, an XY plotter, a printer, etc., it can be used as a material for quality evaluation of the optical disk 1 and defect cause investigation.

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

(1) Reference position data stored in the memory circuit 9 (reference position data b from the code processing circuit 5 and reference position data d from the control circuit 12 to the same defect position data
When the two correspond to each other, they are present on the disk 1 by reading and counting any one of them), or by reading and counting any one of each defect start position data and each defect end position data. You can know the total number of defects.

(2) It is possible to know the number of defects in each sector by performing the same count as in (1) above for each sector of each track and detecting the number of defects in each sector.

In the above, the obtained materials are expressed as numerical values, but it goes without saying that these can also be used as materials for quality evaluation of optical disks.

(3) When the subtraction processing is performed between the defect start position data and the defect end position data of the same defect position data, the data of the defect length along the track is obtained, and the defect length is calculated for each track in the predetermined area. By obtaining data of the length and displaying a two-dimensional pattern similar to the optical disk 1 on the output device 11 based on the data, the defect pattern in this predetermined area can be displayed. Therefore, the specific two-dimensional shape and size of the defect can be known from now on, and it will be the data for investigating the cause of the defect.

(4) The optical disk 1 is divided into a circumferential direction and a radial direction, and the divided area is used as a block. The defect position data is distributed for each block based on the reference position data, and the defect size is determined from the defect position data. The defect rate (the ratio of the total area occupied by the defects in the block to the total area of the recording area of the optical disk 1) for each block is calculated by calculating the data, and the optical disk 1 is output to the optical disk 1 by the output device 11 based on this data. By displaying similar secondary patterns, the defect distribution on the optical disk 1 can be known.

Fig. 3 shows that the surface of the optical disk 1 is divided into 64 in the circumferential direction and 21 in the radial direction, and consists of 1344 blocks. By displaying the difference in defect rate for each block, the optical disk 1 2 shows an example of the defect distribution in FIG.
In the same figure, the size of the block defect rate is represented by the density due to hatching.

(5) By reading all the data stored in the memory circuit 9 and printing it out as it is, the absolute position of the defect on the optical disk can be known. When such a material is used, when the defect on the optical disk 1 is directly observed with a microscope, the position of the defect can be known, and therefore the trouble of finding the defect can be saved.

(6) A sector having a defect can be extracted. This means that when actually using the optical disk 1,
It is possible to specify a sector in which a defect related to the optical disk 1 exists, and therefore, it is possible to prohibit the writing of digital data to the specified sector. As a result, at least digital data can be easily written while avoiding a sector having a defect such that the code cannot be corrected, and the reliability of the optical disk is improved.

So far, examples of materials based on data stored in the memory circuit 9 have been shown, but needless to say, such data can be arbitrarily used as necessary.

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 are counters, 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 described below using the timing chart of FIG.

The clock CK is supplied from the control circuit 12 (FIG. 1) via the input terminal 13, and the reference voltage V ₀ is supplied to the converter 20 via the input terminal 16. For the sake of convenience, the reference voltage source 22 is shown as the source of the reference voltage V ₀ . Further, the read signal a supplied from the input terminal 15 includes only the defect signal N. As described above with reference to FIG. 1, the read signal a from the amplifier 4 is changed to the sync signal, the track address signal and the sector. The address signal is removed. Furthermore, this sync signal is
The reset pulse Rs is supplied from 14 to the counter 17.

Therefore, the counter 17 counts the clock CK,
For each reset pulse (hence the disc 1 (first
Reset pulse for each sector (Figure) and reset pulse value
The count value A that is repeated in the cycle of Rs is output. This count value A is supplied to the latch circuits 18 and 19.

On the other hand, the comparator 20 compares the level of the read signal a with the reference voltage V ₀ to generate the latch pulse Ra representing the defect signal N. Here, it is assumed that the defect signal N lowers the level of the read signal a and the level of the reference voltage V ₀ is set lower than the level of the part of the read signal a which is not the defect signal, so the latch pulse Ra becomes low level. , Its falling edge represents the beginning of the defect signal N, and its rising edge also represents the end. This latch pulse Ra is supplied to the latch circuit 18 as it is, inverted by the inverter 21 and supplied to the latch circuit 19.

The latch circuits 18 and 19 perform the latch operation at the falling edge of the supplied latch pulse. Therefore, the latch circuit 18 latches the count value A of the counter 17 at the trailing edge of the latch pulse Ra. Assuming that the count value A at this time is A ₁ , the latch circuit 18 latches the digital value ₁ and uses this as the previous defect starting point position data Ds.
Output). After that, the latch pulse Ra rises, and accordingly, the latch pulse Ra obtained from the inverter 21 falls, and at the trailing edge, the latch circuit 19 causes the counter 17 to count.
The count value A of is latched. Count value A at this time
The When A _2, latch 19 will latch the digital value A _2, and outputs this to the memory circuit 9 as the previous defect end position data De.

In this way, the defect position data c is obtained.

In the above specific example, the reference voltage V ₀ is constant, but it may be variable. This is a light disk 1
After the whole scanning of FIG. 1 is completed and the data obtained at that time is written in the memory circuit 9, the reference voltage V ₀ is changed and the optical disk 1 is scanned again, and the defect position data is obtained in the same manner as described above. Is obtained and written in the memory circuit 9. That is, the entire scanning of the optical disk 1 is performed a plurality of times, and the reference voltage V ₀ for each overall scanning is made different to obtain the defect position data. The defect position data for each overall scan thus obtained represents the start position and the end position of the defect at the depth of the recording layer of the optical disk 1.

Therefore, by displaying the partial two-dimensional pattern of the optical disc 1 using the obtained defect position data for each whole scan, the shape of the defect for each depth of the recording layer of the optical disc 1 can be known. However, by using all the obtained defect position data and displaying a partial two-dimensional pattern of the optical disc 1 in different colors or densities in the defective portion according to the defect data for each overall scan, the result shown in FIG. As shown, the defects can be displayed in three dimensions. Therefore, not only the planar shape and size of the defect but also the three-dimensional structure of the defect can be known, which is an important material for investigating the nature and cause of the defect. In FIG. 6, the hatched portion represents a defect, and the depth of the defect is represented by the density of the hatching.

In the specific example of FIG. 4, the defect signal N lowers the level of the read signal a. However, when there is a defect that raises the level of the read signal a, in FIG. a signal reading provided another comparator a, different levels of the reference voltage V ₀ '(however, the reference voltage V _0' is the reference voltage V ₀ higher than the level of the level is not defective portion of the read signal a portion of the Such a defect can be detected by comparing with (set), and this defect can be similarly supplied to the latch circuits 18 and 19 as a latch pulse.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain not only the number and distribution of defects on the optical disk, but also data specifically representing the properties of the defects themselves such as shape and size and the positions of the defects. Therefore, it is possible to obtain an excellent effect that it is possible to accurately evaluate the quality of the optical disk and investigate the cause of the defect.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disk defect evaluation apparatus according to the present invention, FIG. 2 is a schematic view showing a concrete example of data written in the memory circuit of FIG. 1, and FIG. FIG. 4 is a pattern diagram showing a defect distribution display of an optical disk according to an example, FIG. 4 is a block diagram showing a specific example of the defect detection circuit in FIG. 1, and FIG. 5 is a timing chart for explaining the operation of this specific example. FIG. 6 is a pattern diagram showing a three-dimensional display of defects on the optical disk according to this embodiment. 1 ... Optical disk, 3 ... Optical head, 5 ... Code processing circuit, 8 ... Defect detection circuit, 9 ... Memory circuit, 10 ...
… Processing circuit, 11 …… Output device, 12 …… Control circuit, 17 …… Counter, 18,19 …… Latch circuit, 20 …… Converter.

Claims (3)

[Claims] 1. A defect evaluation apparatus for an optical disk in which a predictive synchronization signal and an address are written for each track sector, an optical head for sequentially reproducing and scanning the tracks on the optical disk, and the optical head. A code processing circuit for extracting an address signal representing the address of the sector from the read signal from the target head and generating reference position data for each sector, and a defect signal only from the read signal for extracting the defective signal for each defect signal. A defect detection circuit for generating defect position data having a data pair of defect start end position data and defect end data in the sector based on the reference position data, the defect position data and the reference position data corresponding thereto. And a processing circuit that stores a desired data pair from the memory circuit and generates a signal for display, and a processing circuit Signal from the optical disc defect evaluation apparatus, wherein a composed and an output device for performing data display on the defective supplied. 2. The defect detection circuit according to claim 1, wherein the defect detection circuit counts a clock of a constant cycle and is reset for each sync signal of the read signal, the read signal and the reference voltage. Of the counter to generate a pulse indicating the period of the defect signal, a first latch circuit that latches the count value of the counter at the beginning of the pulse, and a count value of the counter at the end of the pulse. A second latch circuit for latching, wherein the output digital value of the first latch circuit is the defect start end position data, and the output digital value of the second latch circuit is the defect end position data. Optical disk defect evaluation device. 3. The optical disk defect evaluation device according to claim (2), wherein the level of the reference voltage is variable.