JP2830336B2 - Optical recording medium initialization method - Google Patents

Description

The present invention relates to a rewritable optical disk, optical card, optical tape, etc., which records, reproduces or erases information by a phase change between an amorphous phase and a crystalline phase. The present invention relates to a method for initializing a phase change optical recording medium.

[Prior Art] An optical recording medium using a phase change generally uses an amorphous state as a recording state and a crystalline state as an erasing state. Such an optical recording medium, for example, recording on an optical disc,
Erasure and reproduction are performed by laser beam irradiation, and recording and reproduction are performed with a conventional spot having a small beam diameter of about 1 μm. An elliptical elongated spot having a radius of about 1 μm in a recording medium direction and about 10 μm in a circumferential direction is used. Erase 2
From the beam method, a single beam overwrite method (N. Yamada et al .. Proc, SPIE 695) that uses a single beam of a small spot with a beam diameter of about 1 μm and can record, erase, and reproduce only by changing its intensity , 79 (1986)).

As a one-beam overwrite type optical disk, it is essential that the crystallization speed of the recording film is high, and a medium having a high crystallization speed is, for example, a Sb2Te3 thin film (Japanese Patent Laid-Open No.
59-185048), Ge-Sb-Te based thin film (JP-A-62-29797).
42 gazette, JP-A-63-225934 gazette, N. Yamada et al, Jpn.
J. Appl. Phys., 26, Suppl., 26-4, 61-66 (1987)), M
-Ge-Sb-Te thin film, M is a metal element such as Pd, Cu, Ag, Tl, Co, etc. (Proceedings of the 50th Annual Meeting of the Japan Society of Applied Physics 29p-PB-37 (1
989 autumn), Proceedings of the 36th JSAP Symposium 1p-ZB-
9) (Spring 1989)), In-Se thin film (T. Nishida et al, Jp.
nJAppl.Phys., 26, Suppl., Suppl., 26-4, 67-70 (198
7)), In-Sb-Te thin film (Y. Maeda et al, J. Appl. Phy
s.64, 1715 (1988)).

These recording films are formed by a vacuum film forming method such as vapor deposition or sputtering, and are generally formed in an amorphous state. Therefore, when used as an optical disk, for example, it is necessary to perform a so-called initialization process in which the recording layer of the entire recording area is once crystallized before recording.

Conventionally, as a method for initializing an optical disc,
Japanese Patent Application Laid-Open No. 60-10631 discloses a method for irradiating a wide range of optical disks with a large-power, continuous-emission argon laser beam as described in Japanese Patent Application Laid-Open No. 60-10631 to initialize the entire recording section in a short time with uniform reflectance. No. 217735, the average cross-sectional area of the crystal grains in the initialized portion and the average cross-sectional area of the crystal grains around the amorphous pits generated during the recording operation and the amorphous pits are brought into a crystalline state by an erasing operation. There has been proposed an initialization method in which the average cross-sectional area of the crystal grains in the set portion is made substantially the same so that the recording signal remains unerased. [Problems to be Solved by the Invention] However, the above-mentioned conventional method has been proposed. In this case, when recording and erasing are repeated, the CN ratio can be obtained stably, but the erasure rate changes and stable characteristics cannot be obtained. That the initial erase rate is low has been a problem returns.

Conventionally, the reason why the erasing rate is poor is that the reflectance of the optical disk after initialization is not uniform and the periphery of the amorphous pits generated by recording is once melted and recrystallized, so that relatively large particles are formed. It has been thought that the change in the crystal state and the difference between the crystal grain size of the crystal, the crystal grain size of the initialization and the crystal grain size of the erasure significantly cause unevenness in the reflectance.

However, according to the study of the present inventors, even if the reflectance is made uniform, the crystal grain size by initialization, the crystal grain size by erasure, and the crystal grain size around the amorphous pit are not necessarily the same. It is difficult to say that the initial erasure rate is good. Rather, factors that determine the crystal state other than the crystal grain size, such as the crystal structure, crystallinity, and orientation, are controlled by the conditions of the initial irradiation power density P and the irradiation time T. It turned out to be important.

However, Japanese Unexamined Patent Publication No. Sho 60-10631 discloses a design method of an optical system for initializing an optical disk at high speed and with uniform reflectance, and an initialization processing apparatus using the same. Since it is not shown that the consideration of whether to make is the most important in realizing a good recording / erasing characteristic, any concrete and effective initialization method for controlling the crystal state of initialization is not described. It does not provide insight. Japanese Patent Application Laid-Open No. Hei 1-217735 controls only the crystal grain size in the crystal state of the initialization, but for other factors, any concrete and effective method for controlling the crystal state of the initialization is effective. It does not give any insights. On the other hand, recently, as shown in the 36th Annual Meeting of the Japan Society of Applied Physics, 1p-ZB-2, the layer structure of the optical disc was devised to increase the cooling rate of the recording layer, and the amorphous pits once melted by recording A method has been proposed in which the erasing rate and the erasing margin are significantly improved by preventing the periphery from being recrystallized. However, even in such a layer configuration of the optical disc, the conventional initialization method does not always correspond, and it is necessary to realize an initialization in which the initial erasure rate is good and the recording and erasing repetition characteristics are stable. I can't say.

The present invention has been made in view of the problems of the prior art described above, and its purpose is to obtain a better CN ratio and erasing rate than the first time when recording and erasing are repeatedly performed, and have excellent stability in repetition. Is to provide a method for initializing an optical recording medium that can obtain the above.

[Means for Solving the Problems] An object of the present invention is to record, erase, and reproduce information by irradiating a recording layer formed on a substrate with light, and to record and erase information. When the optical recording medium is initialized by performing a phase change between an amorphous phase and a crystalline phase, the power density P (mW
/ μm ² ) is 1.0 ≦ P ≦ 5.0 and irradiation time T (μsec) is 1 ≦ P
This is achieved by an optical recording medium initialization method characterized by irradiating a laser beam with T ≦ 100 and changing the recording layer from an amorphous state to a crystalline state only by the laser beam irradiation.

Crystallization of the recording layer of the optical recording medium utilizing the phase change can be obtained by heating the recording layer in a temperature region higher than the crystallization temperature and holding the recording layer for a time necessary for crystallization.

The time (erasing time) required for the recording layer, which has been made amorphous by recording after being crystallized by initialization, to be crystallized by erasing, is, for example, a one-beam overwrite method for recording and erasing information. Sb2Te3 as a rewritable material
Thin film, Ge-Sb-Te thin film, M-Ge-Sb-Te thin film, M is
Metal elements such as Pd, Cu, Ag, Tl, Co, In-Se based thin films, In-Sb
For a Te-based thin film, it is about 50 to 200 nsec. However, when the recording layer after film formation is crystallized by initialization, the amorphous state at the time of film formation is more disorderly than in the amorphous state formed by quenching after melting by recording. Therefore, the crystallization time partially varies. Further, since the initial amorphous state changes depending on the film forming conditions, the same can be said between optical disks.
Therefore, the crystallization time in the initialization is long, and if the laser irradiation time is short, crystallization cannot be performed completely, and it is difficult to obtain a uniform crystal state. Therefore, in the case of initialization, in order to perform crystallization uniformly and completely, it is necessary to lengthen the irradiation time of the laser beam and lengthen the holding time of the crystallization temperature. Prolonging the irradiation time by increasing the laser beam diameter delays the heat outflow of the recording layer due to the heat storage effect, and the time for maintaining the temperature equal to or higher than the crystallization temperature can be longer than the actual irradiation time. More effective. Here, the irradiation time means the time during which the full width at half maximum of the laser beam passes through a certain point on the optical disk.

The irradiation time is preferably in the range of 1 μsec to 100 μsec, more preferably 10 μsec to 50 μsec. If the time is less than 1 μsec, crystallization tends to be uneven, and the reliability is reduced by one initialization. If it is longer than 100 μsec, the initialization time becomes longer, and the temperature of the substrate rises due to heat diffusion from the recording layer, causing thermal deformation and causing noise.

The optimum laser beam power density for such an irradiation time varies depending on the material and layer configuration of the optical recording medium, but is 1.0 mW /
μm ² to 5.0 mW / μm ² is preferable, more preferably
Is a ^{1.0mW / μm 2 ~3.0mW / μm 2} . If it is less than 1.0 mW / μm ² , it takes a long time to crystallize, and if the irradiation time is prolonged, it may not crystallize.If it is more than 5.0 mW / μm ² , defects such as film distortion of the recording layer due to heat may occur. Is likely to occur and causes noise.

As a laser light source of the present invention, an argon laser,
A gas laser such as a helium / cadmium laser, a semiconductor laser, or the like is used. In particular, the use of a semiconductor laser is preferable because the device can be downsized and power consumption is small.

One example of an apparatus for initializing an optical recording medium by a method of the present invention using a semiconductor laser will be described with reference to FIG.
The initialization device is not particularly limited to this.

In FIG. 1, 1 is an optical disk, 2 is a semiconductor laser that emits laser light 3, 4 is a collimator lens for making the laser light 3 parallel, 5 is an astigmatic difference correction lens, 6
Denotes a mirror, 7 denotes an objective lens, 8 denotes a motor, and 9 denotes a moving table. The laser light 3 emitted from the semiconductor laser 2 is converted into parallel light by a collimator lens 4, and is parallelized by a astigmatic difference correction lens 5 in a direction parallel to the pn junction surface of the semiconductor laser 2.
The correction is performed so that the same position is focused in the vertical direction. Further, the light is irradiated as an elliptical spot on the recording layer of the optical recording medium via the mirror 6 and the objective lens 7. Optical system including these
10 is fed by the moving table 9 in the radial direction of the optical recording medium 1 at an appropriate feed pitch. On the other hand, the optical recording medium 1 is rotated by a motor 8.

The rotation of the optical recording medium can be set freely within the above irradiation time range, but it is preferable to keep the moving linear velocity constant in order to keep the laser light irradiation time constant in all the initialization portions of the recording medium. When the linear velocity is low, it takes a considerable amount of time to initialize the entire recording portion of the recording medium, and in some cases, the film may be destroyed by heat, and when the linear velocity is high, the surface deflection of the optical disc increases. Therefore, the linear velocity is 3m / s
A range of 4040 m / s is preferred.

The configuration of the optical recording medium is not particularly limited.
For example, as shown in FIG. 2, a dielectric layer 12 is formed on a disk substrate 11 having good recording / erasing characteristics of the beam overwrite method.
a, recording layer 13, dielectric layer 12b, reflective cooling layer 14, and protective layer
A laminated structure in which 15 are sequentially laminated is preferable because more preferable effects can be expected by applying the initialization method of the present invention. Here, the protective layer is, for example, 5 μm to 40 μm.
A resin protective layer such as an ultraviolet curable resin layer having a thickness of m can be used. Further, an adhesive layer may be provided on the protective layer and bonded to another substrate. As the disk substrate, when performing recording and erasing from the substrate side, it is preferable to use a material through which laser light is transmitted, for example, a polymer resin such as polymethyl methacrylate resin, polycarbonate resin, epoxy resin, polyolefin resin, or glass. No.

The dielectric layer is a deformation-preventing layer that prevents the substrate and the recording layer from being deformed by heat due to recording and thereby deteriorating the recording and erasing characteristics, a protective layer that has the moisture-heat resistance and oxidation-resistance of the recording layer, and the recording layer. Plays the role of a diffusion prevention layer for preventing diffusion of atoms from the semiconductor to the reflection layer. As such a dielectric layer, for example, an inorganic film such as ZnS, SiO ₂ , Ta ₂ O ₅ , ITO, ZrC, TiC, MgF ₂ or a mixed film thereof can be used. In particular, a mixed film of ZnS and MgF ₂ is preferable because it has excellent wet heat resistance and suppresses deterioration of the recording layer due to repeated recording / erasing. The recording layer is preferably a material having a high crystallization rate as an optical recording medium for performing recording and erasing of a one-beam overwrite method. For example, a Ge-Sb-Te-based thin film, an M-Ge-Sb-Te-based thin film, and M are
Examples include metal elements such as Pd, Cu, Ag, Tl, and Co, and In-Sb-Te-based thin films. In particular, when an optical recording medium using a Pd-Ge-Sb-Te-based thin film as a recording layer is initialized by the method of the present invention, when the crystal structure shifts from an amorphous phase to a crystalline phase, the movement of atoms is reduced. Since it has a simple face-centered cubic structure and can be made into a single phase, not only the crystallization speed is increased,
It is preferable because phase separation and composition segregation hardly occur even when recording and erasing are repeated, and thermal stability is excellent.

The reflective cooling layer facilitates heat diffusion from the dielectric layer and increases the cooling rate of the recording layer melted during recording,
It facilitates formation of amorphous pits. Also, there is an effect of preventing the dielectric layer and the like from being thermally deformed, and an effect of improving the contrast of a reproduced signal by optical interference. Such a reflective cooling layer includes a metal or a metal oxide, a metal nitride, a metal carbide, or the like, which has light reflectivity and absorptivity at the wavelength of laser light and has higher thermal conductivity than the dielectric layer. A mixture of, for example, Zr, Hf, Ti, Ta, Mo, Si, Al, Au and the like, alloys thereof, these Zr oxides, Si oxides,
What mixed Si nitride, Al oxide, etc. can be used.
In particular, Al, Au, Ta, alloys thereof, and the like are preferable because the film can be easily formed and the thermal conductivity can be adjusted over a wide range by selecting a material.

The thickness of the dielectric layer, recording layer and reflective cooling layer is 50 nm to 300 nm for the 12a dielectric layer and 10 nm for the 12b dielectric layer.
A recording layer having a thickness of 30 nm, a recording layer having a thickness of 10 nm to 60 nm, and a reflection cooling layer having a thickness of 20 nm to 100 nm is suitable for an optical recording medium in which recording and erasing is performed by a one-beam overwrite method.

Examples of the method for forming the dielectric layer, the recording layer and the reflection cooling layer on the disk substrate include a known thin film forming method in a vacuum, for example, a vacuum deposition method, an ion plating method, a sputtering method, and the like. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled.

EXAMPLES Hereinafter, the present invention will be described specifically based on examples of the present invention, but the present invention is not limited thereto.

The characteristics in the examples were evaluated based on the following methods.

(1) Composition For the composition of the recording layer and the dielectric layer, the content of each element was determined by ICP emission spectrometry (FTS-1100 type manufactured by Seiko Instruments Inc.), and the composition ratio was calculated.

(2) Recording / erasing characteristics (one-beam overwrite characteristics) The initialized optical recording medium is rotated at 9 m / s, and the recording power is modulated from the substrate side at a frequency of 5.3 MHz and a pulse width of 60 ns by 15 m.
A semiconductor laser beam having a wavelength of 780 nm and a erasing power of 8 mW was condensed and irradiated with an objective lens having a numerical aperture of 0.5 to perform overwrite recording.

After the recording, the recorded portion was scanned with a 1.5 mW semiconductor laser beam to reproduce the recorded data. In addition, the frequency of the recording condition was changed to 2.0 MHz and the overwrite recording was performed.
After erasing the recording signal of Hz, reproduction was performed under the same conditions as above. The carrier level and noise level of the reproduced signal after recording and after erasing were measured by a spectrum analyzer, and the carrier-to-noise ratio (C / N) was determined under the condition of a bandwidth of 30 kHz. The difference in carrier level at 5.3 MHz during recording at 2.0 MHz (when erasing at 5.3 MHz) was determined as the erasing rate.

The repetition is performed by alternately performing 5.3 MHz and 2.0 MHz overwrite recordings five times. In each case, the erasure rate of the 5.3 MHz recording signal is obtained in the same manner as the first time, and then the 5.3 MHz overwrite recording is repeated 1000 times. After that, 5.3M as well as the first time
The erasure rate of the Hz recording signal was obtained and evaluated.

(3) State of Film Destruction of Recording Layer Due to Initialization The state of film destruction of the recording layer due to initialization was measured by comparing noise at 1.0 MHz between the optical recording medium after film formation and the optical recording medium after initialization.

(4) Crystal structure The crystal structure was compared by measuring the X-ray diffraction spectrum by the wide-angle X-ray diffraction method. For the measurement, a thin film diffraction device (X-ray generator RU200B manufactured by Rigaku Denki) and a goniometer 2155 manufactured by Rigaku
Type D, a counting recorder RAD-B manufactured by the company, and a scintillation canter) were used. The incident angle of X-rays was set to 0.5 degree with respect to the recording layer surface. The scanning method was 2θ and continuous scanning. CuKα radiation was used as the X-ray source.

(5) Crystal grain size The crystal grain size was observed and compared with a transmission electron microscope (H-800UHR, manufactured by Hitachi, Ltd.). The observation was performed at an acceleration voltage of 200 kV.

Example 1 A recording layer, a dielectric layer, and a reflection cooling layer were formed by an RF magnetron sputtering method while a polycarbonate substrate with a spiral groove having a thickness of 1.2 mm, a diameter of 130 mm, and a pitch of 1.6 μm was rotated at 60 rpm.

First, after evacuation to 7 × 10 ⁻⁵ Pa, the molar ratio of ZnS to MgF ₂ was 90:10 on a substrate in an argon gas atmosphere of 6 × 10 ⁻¹ Pa.
160nm of the ZnS-MgF ₂ dielectric layer by sputtering
Pd2Ge17Sb29T by co-sputtering while monitoring Ge, Sb, Te, and Pd with a quartz crystal film thickness meter
A recording layer having an element composition of e52 was formed to a thickness of 30 nm. Further, ZnS-MgF ₂ of the above-mentioned dielectric layer was 30n by sputtering method.
m, Au was formed thereon as a reflective cooling layer to a thickness of 50 nm. Finally, an ultraviolet curable resin on the Au layer was applied by spin coating, and then irradiated with ultraviolet light to be cured to form a 10 μm protective layer. Thus, an optical recording medium on which the initialization method of the present invention was performed was obtained.

For initialization, set the power density to 1.0 mW / μm ² and the irradiation time to 12 μ
Performed in sec. At this time, the laser beam spot of the apparatus shown in FIG.
22 μm, 66 μm in the circumferential direction, the rotation speed of the optical disk was 5.5 m / s, and the feed pitch for one rotation of the optical disk was 2 μm.

The recording / erasing characteristics of the initialized optical recording medium in overwriting were evaluated by the above evaluation method. As a result, the first
C / N is 51.2dB, erasing rate 30.1dB, 5th C / N is 0.5dB, erasing rate is 28.2dB, 1000th C / N is 50.7dB, erasing rate is 28.0dB,
And a better C / N and erasing rate than the first time were obtained, and were stable in repetition, and excellent recording / erasing characteristics were obtained.
The X-ray diffraction spectrum of the recording layer after the initialization was measured. FIG. 3 is a graph showing the relative intensity of the measured X-ray diffraction spectrum, and 16 is the vertical axis of the graph, which represents the relative intensity of the diffraction line. Reference numeral 17 denotes the horizontal axis of the graph, which indicates the diffraction angle 2θ (unit: degree). 18 is 200
Planes, 19 is 220 planes, 20 is 400 planes, and 22 is 420 planes. As a result of diffraction spectrum measurement, the crystal structure of the recording layer after the initialization was a face-centered cubic structure.

When the crystal grain size after recording and erasing once is examined, the erased portion is considerably larger than the initialized portion and is twice or more. Even though the grain size is not uniform, excellent recording and erasing characteristics are obtained. It was shown.

Comparative Example 1 The power density was 10.0 mW / μm ² and the irradiation time was 0.3 μsec.
Initialization was performed in the same manner as in Example 1 except that the above was set. At this time, the laser beam spot has a full width at half maximum in the radial direction of the optical disk of 1.6 μm, a circumferential direction of 1.2 μm, and a linear velocity of
It was 4 m / s. Noise level rise by initialization is 3dB
And became quite large.

The initialized optical recording medium was overwritten to evaluate the recording / erasing characteristics by the above-mentioned evaluation method. As a result, the first C /
N is 51.8dB, erasure rate 21.4dB, 5th C / N is 52.5dB, erasure rate 26.1dB, 1000th C / N is 51.7dB, erasure rate 23.9dB, and C
Although / N was stable, the erasing rate was poor, and there was a large fluctuation in repetition, and excellent recording / erasing characteristics could not be obtained.

Comparative Example 2 Initialization was performed in the same manner as in Example 1 except that the power density was 1.0 mW / μm ² and the irradiation time was 0.5 μsec. At this time, the laser beam spot has a full width at half maximum in the radial direction of the optical disk of 1.
6 μm, the circumferential direction was 5 μm, and the linear velocity was 10 m / s.

The noise level hardly increased due to the initialization.

The overwrite recording / erasing characteristics of the initialized optical disk were evaluated by the evaluation method described above. As a result, the reflectance after initialization was almost constant, but the first C / N was 50.2 d.
B: The erasure rate was 17.4 dB, and excellent recording / erasing characteristics could not be obtained.

Comparative Example 3 Initialization was performed in the same manner as in Example 1 except that the power density was 6.0 mW / μm ² and the irradiation time was 2 μsec. At this time, the laser beam spot had a full width at half maximum in the radial direction of the optical disk of 12 μm, a circumferential direction of 20 μm, and a linear velocity of 10 m / s.

 Initialization caused film destruction of the recording layer.

[Effects of the Invention] As described above, according to the present invention, the optical recording medium utilizing the phase change is initialized with a laser beam having a specific power density for a specific irradiation time, so that the recording layer is crystallized without distortion. Can be completely performed. Therefore, the optical recording medium according to the present invention can obtain a better erasing rate than the first time,
There is an advantage that excellent stability can be obtained even in repetition.

[Brief description of the drawings]

FIG. 1 is an explanatory view of one example of an initialization apparatus used for carrying out the method of the present invention, FIG. 2 is an explanatory view of one example of an optical recording medium, and FIG. 3 is an X-ray diffraction of a recording layer after initialization. FIG. 3 is a schematic diagram illustrating an example of a spectrum. 1: optical disk, 2: semiconductor laser, 3: laser beam, 4: collimator lens, 5: astigmatic lens, 6: mirror, 7: objective lens, 8: motor, 9: movable base, 11: disk substrate, 12a: dielectric layer, 12b: dielectric layer, 13: recording layer, 14: reflective cooling layer, 15: protective layer.

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁶ , DB name) G11B 7/26 G11B 7/00

Claims (1)

(57) [Claims] An information recording, erasing and reproducing operation can be performed by irradiating a recording layer formed on a substrate with light, and information recording and erasing can be performed by using a phase between an amorphous phase and a crystalline phase. When the optical recording medium is initialized by the change, the optical recording medium has a power density P (mW / μm ² ) of 1.0.
The recording layer is changed from an amorphous state to a crystalline state only by irradiating a laser beam with ≦ P ≦ 5.0 and an irradiation time T (μsec) of 1 ≦ T ≦ 100. Initialization method of optical recording medium.