JP2757585B2 - Sampling inspection method at the time of manufacturing phase change type optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sampling inspection method at the time of manufacturing an overwritable phase-change optical information recording medium, which utilizes the fact that the recording layer reversibly changes phase upon irradiation with a laser beam. It is about.

[0002]

2. Description of the Related Art In recent years, as the amount of information has increased, there has been a demand for a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed. However, an optical disk is expected to exactly meet such a use. I have. Optical discs include a write-once type, which allows recording only once, and a rewritable type, which allows recording / erasing any number of times.

[0003] Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a reflectance change accompanying a reversible change in crystal state. The phase change medium does not require an external magnetic field, and has the advantage that recording and erasing can be performed only by modulating the power of laser light, and the recording and reproducing apparatus can be downsized. Furthermore, so-called one-beam overwriting, in which erasing and re-recording are performed simultaneously with a single laser light beam, is possible.

As a recording layer material of such a phase change medium capable of one-beam overwriting, a chalcogen alloy thin film is often used. For example, GeSbTe
System, InSbTe system, GeSnTe system and the like.
In an actual medium, the recording layer is usually sandwiched between dielectric layers to prevent repetitive deterioration due to overwriting, or to improve the reflectance difference (contrast) by using an interference effect.

Generally, in a rewritable phase change recording medium, an unrecorded / erased state is changed to a crystalline state, and an amorphous bit is formed. The amorphous bits are formed by heating the recording layer to a temperature higher than the melting point (600 ° C. or higher in the case of GeSbTe) and rapidly cooling it. In this case, the dielectric layer functions as a heat radiation layer for obtaining a sufficient supercooled state. On the other hand, erasing (crystallization) is performed by heating the recording layer to a temperature higher than the crystallization temperature of the recording layer and lower than the melting point.

In this case, the dielectric layer functions as a heat storage layer for keeping the temperature of the recording layer high until crystallization is completed.
When overwriting is performed repeatedly, heating and
Deformation due to melting and volume expansion of the recording layer during cooling, crack generation inside the dielectric protection layer and peeling at the interface of each layer,
Due to the thermal deformation of the plastic substrate, a reproduced signal is deteriorated such as a defect or an increase in noise level.

In the phase change medium, since the recording layer is heated to a high temperature equal to or higher than the melting point, it is necessary to pay particular attention to the deterioration due to repeated overwriting. At present, it has been developed almost no deterioration occurs medium at 10 ⁶ times repeated overwriting by improving the layer structure, the protective layer material,
It has almost reached the practical stage.

The problem here is how to guarantee the reliability of the phase change medium as a product. As described above, the specific materials and layer configuration according Invite laboratory, but ¹⁰⁶ times repetitive overwriting of became possible, such a characteristic in all tracks of all the disks always be realized Absent. That is, deterioration due to repeated overwriting, especially defects,
It grows around pinholes and dust that originally existed.

The number of such initial defects varies between disks and between tracks on the same disk.
The rate of generation of defects due to repeated overwriting also differs. As a method for ensuring the reliability of under phase-change medium such circumstances, have a separate alternating tracks for repetitive overwriting number of times counted to keep 10 ⁵ times repeated overwriting track of each track or sector A way to do that has been proposed. (Fukushima, Takagi, Sato, Optical Memory Symposium, '90, Proceedings)

[0010]

On the other hand, it is widely practiced in such information recording media to perform defect inspection on a production line and remove defective products. However, in many cases, an initial defect serving as a nucleus of a defect due to repeated overwriting cannot be detected as long as actual overwriting is not performed. Therefore, it is necessary to select at least some tracks from each disk by sampling inspection and to actually perform overwriting repeatedly (cycle test).

[0011] For example, a cycle test of 10 ⁶ times requires several hours to 10 hours, and it is almost impossible to introduce even a sampling inspection into an actual production line. The sampling inspection method of the present invention
Remove one or several disks from many disks and
Inspect disks in a short time and check the quality of disks in the whole lot
This is an inspection for determination.

[0012]

The inventors of the present invention conducted accelerated cycle tests and examined various methods for evaluating the repetition characteristics of each disk in a short time. Closely related, if the same track is repeatedly irradiated with laser light, defects can be generated and grown only when the power is applied to form amorphous bits, that is, when the recording layer is melted. all right.

Further, it was also found that when the laser having the power for melting the recording layer was irradiated in a DC state instead of a pulse state, the deterioration was faster than in the case of a pulsed, ie, discontinuous, irradiation. Therefore, if the cycle test is accelerated by repeatedly irradiating the laser beam having the intensity necessary for amorphizing the recording layer on the same track provided on the substrate in advance with direct current (unmodulated), the cycle test can be performed more conventionally. The present inventors have found that the inspection time can be greatly reduced, and arrived at the present invention. Of course, the disc used for inspection is irradiated with a laser.
That is, the recording layer in the damaged portion is destroyed.

Hereinafter, the contents of the present invention will be described in detail. As an example of the layer configuration of the phase change recording medium, a substrate, a first dielectric protection layer, a recording layer, a second dielectric protection layer, a metal reflection layer, a hard coat layer made of a thermosetting or ultraviolet curing resin are sequentially formed. And the like. Each layer other than the hard code layer can be formed by a sputtering method or a vapor deposition method. However, it is preferable to use a sputtering method which is excellent in mass productivity and to form a film in an in-line apparatus which forms a film in a consistent vacuum.

The thickness of each layer is selected in consideration of the optical interference effect so as to increase the difference (contrast) in the reflectance between the crystalline state and the amorphous state. The adjustment is also made to optimize the temperature and cooling rate of each layer during recording / erasing.

Examples of the substrate include transparent resins such as polycarbonate, acrylic and polyolefin, and glass. A chalcogen-based alloy thin film is often used as the recording layer. For example, InSbTe, GeSbTe,
Ternary alloys such as GeSnTe and Ta and C
o, Ag, etc. are added. In particular, GeS
The bTe ternary alloy system has a high crystallization rate, excellent stability over time of the amorphous bit, and has practically sufficient characteristics.

The first and second dielectric protection layers are preferably made of a dielectric material which has excellent adhesion to a substrate or a recording layer and has excellent heat resistance and mechanical strength. Specific examples include metal oxides such as Si, Al, Ta, and Zr, nitrides, and carbides. Also, ZnS
A mixture of and metal oxide is also used. (Japanese Unexamined Patent Publication No.
167090, 63-102048, 63-276
724)

As the metal reflection layer, an alloy thin film containing Au or Al as a main component is used. The recording medium having the above-described layer configuration is formed on a substrate on which a groove for tracking a light beam is formed in advance by a method such as injection molding. Generally, a light beam enters from the substrate side and reads reflected light through the substrate. Normally, one-beam overwriting is performed by superposing a recording power in a pulse shape on a fixed erasing power. In a normal cycle test, a recording pulse of a single frequency is repeatedly irradiated on the same track, recording pulses of two kinds of frequencies are alternately and repeatedly irradiated, or a pulse of a random pattern (for example, 2-7 code) is repeatedly irradiated. Or After a predetermined number of repeated overwrites, C /
Read N ratio, erase ratio, error rate, and jitter.

However, this method requires a long time to obtain a result as described above. In the inspection method of the present invention, a laser beam of DC power is repeatedly irradiated on the same track without pulse modulation of the recording power. The laser power at the time of inspection may be applied by changing the normal recording power to DC, and may be changed depending on the case. However, a large power that causes a large change in the dielectric layers on both sides of the recording layer cannot be used. When a laser beam of DC power is irradiated, the recording layer becomes uniformly amorphous, and the reflectance is lower than the initial crystallization state. In this state, after overwriting at a specific frequency, the C / N ratio, erasing ratio, jitter, and error rate can be evaluated. However, the noise level and drop-in defect of the reproduced signal can be detected without overwriting. It is also possible to quantitatively evaluate the degree of deterioration.

The inspection method of the present invention aims at evaluating defects not detected particularly in the initial defect inspection.
For this purpose, it is sufficient to measure the drop-in defect. When applying the test method of the present invention, when the cycle test, for example, conventional single frequency, even in media such as the error rate begins to increase after 10 ⁵ times 1
0 ^four times is detected by an increase of the drop-in defects, can significantly reduce the time required for the cycle test, completed in about 30 minutes per track. Further, with respect to the tendency of the number of defects and the rate of increase, the same tendency is obtained between the ordinary cycle test and the inspection method of the present invention.

A good correlation can be obtained for the correlation coefficient and the like for associating the numbers of the two defects with the irradiation laser power and the measuring device. This inspection is a destructive inspection, and it is effective to provide an inspection track separately from a normal recording area, for example, on the inner or outer periphery of the recording track.

[0022]

The present invention will be described below with reference to examples. The layer structure of the phase change recording medium used in the embodiments described below is substrate / first dielectric layer / recording layer / second dielectric layer / reflective layer /
It is a hard coat layer. As a substrate, a spiral group was provided on the surface, and the thickness was 1.2 mm, and the diameter was 130 mm.
Was used. The track pitch was 1.6 μm and recording was performed on the land. As the recording layer, a composition of Ge14Sb34Te52 (atomic%)
The original alloy was formed to a thickness of 700 ° by a DC sputtering method. Further, a DC voltage was applied to a Ta target in a mixed gas of oxygen and argon, and reactive sputtering was performed to produce a tantalum oxide dielectric layer. The thickness of the dielectric layer on the side in contact with the substrate is 1100 °, and the thickness of the dielectric layer above the recording layer is 1500 °. An Al alloy thin film having a thickness of 500 ° was formed as a metal reflective layer by a direct current sputtering method. An ultraviolet curable resin having a thickness of 4 μm was used as the hard coat layer.

The cycle test has a radius of 15 mm to 20 m.
The rotation was performed at a linear velocity of 10 m / sec on the track positioned at m. The unmodulated recording power is 15 mw. FIG. 1A shows a change in noise level with the number of repetitions. It can be seen that the 10 ^four times sharply since the noise is increasing. At the same time, burst errors were observed to increase rapidly. These defects mostly initial defects (pinholes, dust, etc.) is due to the, detects sufficient defect in about 10 ⁴ times, can evaluate durability against repeated overwriting of the disk. The time required for this evaluation is 10 minutes in 10 ⁴ times, it was about 30 minutes at 10 ⁵ times.

Comparative Example 1 A disk having the same structure as that used in Example 1 was subjected to a normal cycle test. That is, recording power 1
5mw, erasing power 7 mW, was subjected to repeated overwriting at frequency 4 MHz, 50% duty single frequency, an increase in the noise level was observed in 10 ⁵ or later, as shown in FIG. 1 (b). At the same time, burst errors began to appear and increased rapidly. This burst error is caused by an initial defect as in the first embodiment. The time required for this evaluation is 30 minutes to 10 ⁵ times, was 5,6 hours at ¹⁰⁶ times.

[0025] For discs having the same structure as used in Comparative Example 2 Example 1 was irradiated repeatedly erasing power 7 mW, even after ¹⁰⁵ times, not observed no change in the noise level, some burst Only errors were detected. This is because the recording layer is not melted, and in the evaluation method of the present invention,
It is necessary to irradiate a laser beam power to melt the recording layer.

Example 2 Five types of discs having the same layer structure as used in Example 1, but having different repetition durability by changing the layer thickness and the layer forming conditions were obtained. On the other hand, a cycle test was performed by the method according to the present invention and the normal method shown in Comparative Example 1, and the results were compared. The repetition durability was represented by the number of repetitions when the initial noise level increased by 3 db. Table 1 shows the results. It can be seen that the method according to the invention has a good correlation with the normal method.

[0027]

[Table 1]

According to the method of the present invention, the durability of a phase change optical disk can be inspected in a short time.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in noise level.

[Explanation of symbols]

 (A): Example 1 (b): Comparative Example 1

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takashi Ohno 1000-3 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Prefecture Inside Ryoshi Kasei Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/00

Claims (1)

(57) [Claims] 1. An optical information recording medium for recording / erasing / reproducing information by utilizing an optical change accompanying a reversible phase change between a crystalline state and an amorphous state induced by laser light irradiation. A method for inspecting the degree of deterioration in the case where recording and erasing are repeatedly performed on the same track previously formed on a substrate, wherein a laser beam having a DC power having a strength capable of amorphizing the recording layer is used. When manufacturing a phase change type optical information recording medium that inspects the degree of deterioration due to repeated recording by repeatedly irradiating the same track.
Sampling inspection method.