JPH04113519A - Method for initializing optical recording medium - Google Patents

Abstract

PURPOSE:To allow the uniform initialization over the entire surface of an optical recording medium by irradiating this recording medium with the radiation light formed by using two laser beams and synthesizing these beams by shifting the shifting width of the optical axes in the direction perpendicular to the relative moving direction of the optical recording medium in a specific range. CONSTITUTION:The recording layer 19 of the optical recording medium 1 is irradiated with the radiation light formed by using the two laser beams respectively having 2mum<=L<=100mum half-amplitude full width L and synthesizing these beams by shifting the shifting width M of the optical axes in the direction perpendicular to the relative moving direction of the optical recording medium 1 in the l/4<=M<=7L/4 range, by which the amorphous state of this recording layer is changed to a crystalline state. Since the two laser beams are used and are synthesized under the specific conditions in this case, the light intensity distribution can be changed without lowering the max. power and the radiation light formed by synthesizing the two laser beams has the light intensity larger than the light intensity of the single laser light. Uniform parts increase and the spot diameter increases as well. The feed pitch in the radial direction of the optical recording medium is increased in this way and the linear speed of the initialization is increased. The time for processing the initialization is shortened and the productivity is improved. In addition, the recording and erasing characteristics are good over the entire part of the optical recording medium 1. The uniform characteristics are thus obtd.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is applicable to rewritable optical discs, optical cards, optical tapes, etc. that record, reproduce, or erase information through 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] A rewritable optical recording medium using phase change is generally used in an amorphous state as a recording state and in a crystalline state as an erasing state. Recording, erasing, and reproducing on optical recording media are performed by irradiating laser light, and recording and reproducing are performed using a small spot with a conventional beam diameter of about 1 μm. From the 2-beam method that performs erasing using an elongated elliptical spot, to the 1-beam override method, which uses a single beam with a small beam diameter of about 1 μm and can record, erase, and playback simply by changing its intensity. For an optical recording medium using the 1-beam override method, it is essential that the recording film has a fast crystallization speed. Ge-8b-Te based thin film (JP-A-62-209742, JP-A-53-22)
5934 Publication, N. Yamada et at, Ipn.
, J. Appl, Phys., 26.5upp.
1. , 26-4.61-66 (1987)), M
-Ge-8b-Te based thin film ((M is Pd, Cu,
Metal elements such as Ag, TI, Go) (50th Japan Society of Applied Physics Academic Conference Proceedings 29p-PB-37, 36th Japan Society of Applied Physics Academic Conference Proceedings 1p4B-9) ), I n-
8e series thin film (T, N15hida el a, l,
Jpn, J., Appl, Phys., 26S.
upp1. , 5upp1. , 26-4.67-70
(1987)), In-8bTe thin film (Y, Ma
eda ef al, J, Appl, Phys.
64.1715 (1988)) have been proposed.

These recording films are formed by vacuum film forming methods such as vapor deposition and sputtering, and are generally formed in an amorphous state. Therefore, when used as an optical recording medium, the recording layer in the entire recording area must be brought into a crystalline state before recording.
It is necessary to perform so-called initialization processing.

Conventionally, as a method for initializing an optical recording medium, Japanese Patent Laid-Open No. 6
0-10631, a method of irradiating a wide range of optical recording media with argon laser light continuously emitted with high power to initialize the entire surface of the recording area in a short period of time so that the reflectance is uniform, and JP-A No. 0-10631 Interference light formed by using a diffraction grating to form a laser beam with a large spot diameter as shown in Publication No. 63-31046, or a laser beam with a large spot diameter as shown in Japanese Patent Application Laid-Open No. 63-31 [1471] The interference light is split into two parts using a splitter and then overlapped to form interference light, which is then irradiated so that the bright and dark parts are aligned in the radial direction of the optical recording medium to reduce thermal distortion of the optical recording medium and further reduce micro-cracks in the protective layer. There is a known method of initializing to prevent this from occurring.

[Problems to be Solved by the Invention] However, in the conventional method described above, unless the laser beam profile is actively controlled, the light intensity distribution becomes a Gaussian distribution with the maximum power at the center, and the reflection level at the initialization part A similar distribution occurs in . therefore,
In order to uniformly initialize the entire surface of an optical recording medium, the feed pitch in the direction perpendicular to the direction of relative movement of the optical recording medium, that is, in the radial direction, must be much smaller than the initialization width, otherwise the reflection level will become uneven, and recording and erasing will occur. Not only cannot stable characteristics be obtained, but when the power is increased, the film tends to be destroyed by heat in the center. Further, if the feed pitch is set so as to make the reflection level uniform, the processing time for initializing the optical recording medium becomes long, which poses a problem in productivity.

As a means to solve this problem, Japanese Patent Application Laid-Open No. 60-10631
There is a known method, as shown in the publication, in which a cylindrical lens is used to make a laser beam a diverging beam larger than the aperture diameter of an objective lens, and a focus servo is applied to the parallel beam to make the light intensity distribution in the radial direction of the optical recording medium almost uniform. was. However, with this method, the maximum power decreases, so in order to increase the initialization processing time, it is necessary to slow down the linear velocity of movement of the optical recording medium during initialization or increase the power. It's hard to say that it improves sex. Furthermore, the laser beam spot is quite large, and if you try to obtain a larger initialization width, even if the light intensity density is the same, heat will accumulate more easily in the center than in the periphery, and the temperature distribution will be uneven, resulting in uneven reflection levels. The problem is that the central part becomes more susceptible to thermal distortion, microcracks occur especially in the protective layer of the optical recording medium, the moisture and heat resistance and repeatability of recording and erasing deteriorate, and the service life decreases. be.

As a solution to this problem, Japanese Patent Application Laid-Open No. 63-31046
Interference light formed by using a diffraction grating to form a laser beam with a large spot diameter as shown in the publication, and Japanese Patent Application Laid-Open No. 63-310
A laser beam with a large spot diameter as shown in Publication No. 471 is divided into two parts using a beam splitter, and then the interference light formed by superimposing the light is applied to an optical recording medium so that the bright and dark areas are aligned in the radial direction of the optical recording medium. A method has been proposed in which the thermal distortion is reduced by irradiating the object and relaxing the distortion in the irradiated area with the unirradiated area, but this method has the disadvantage that the optical system becomes extremely complex. was there.

The present invention has been devised in view of the problems of the prior art, and its objectives are to provide a uniform reflection level, no thermal destruction or distortion of the film, high speed, and a simple optical system to provide good recording and recording. It is an object of the present invention to provide a method for initializing an optical recording medium with high productivity that provides erasing characteristics.

[Means for Solving the Problems] An object of the present invention is to make it possible to record, erase, and reproduce information by irradiating a recording layer formed on a substrate with light; , when initializing an optical recording medium performed by a phase change between an amorphous phase and a crystalline phase, the full width at half maximum is only 2 μm≦L≦100, respectively.
A shift width M of the optical axis in a direction perpendicular to the relative movement direction of the optical recording medium using two laser beams having a diameter of μm.
An initial stage of an optical recording medium, characterized in that the recording layer of the optical recording medium is changed from an amorphous state to a crystalline state by irradiating with synchrotron radiation light synthesized by shifting L/4≦M≦7L/4. This is achieved by a method of

Since the present invention uses two laser beams and synthesizes them under specific conditions, it is possible to change the light intensity distribution without reducing the maximum power, and the synchrotron radiation light obtained by combining the two laser beams has a light intensity of is larger than that of a single laser beam, the uniform area increases, and the spot diameter also increases, which increases the radial feed pitch of the optical recording medium and increases the linear speed of initialization. Processing time can be considerably shortened, productivity can be improved, and good and uniform recording and erasing characteristics can be obtained over the entire optical recording medium.

As the light source of the laser beam of the present invention, gas lasers such as argon lasers, helium-cadmium lasers, semiconductor lasers, etc. are used, but in particular, the use of semiconductor lasers is preferable because the device can be made smaller and its power consumption is lower. preferable.

A specific example of an apparatus for initializing an optical recording medium by the method of the present invention using a semiconductor laser will be described with reference to FIG. 1, but the initializing apparatus is not particularly limited to this.

In FIG. 1, 1 is an optical recording medium. 2.5 emits a laser beam 3.6 with a semiconductor laser, and converts the laser beam 3.6 into parallel light with a collimator lens 4.7. 8 is a polarizing beam splitter that combines laser beams 3 and 6 to form laser beam 13.
shall be. A half-wave plate 9 combines elliptical laser beams in parallel with a polarizing beam splitter 8. Reference numeral 10 indicates an astigmatism correction lens which corrects the laser beam 13 obtained by combining the semiconductor lasers 2.5 so that the laser beam 13 is focused at the same position in parallel and perpendicular directions to the pn junction surface. Thereafter, the laser beam 13 passes through the mirror 11 and the objective lens 12 and is irradiated onto the recording layer of the optical recording medium. These optical systems 16 are fed by the movable table 15 in the radial direction of the optical recording medium 1 at appropriate feeding pitches. On the other hand, the optical recording medium 1 is rotated by a motor 14.

The full width at half maximum of the two laser beams of the semiconductor laser 2.5 is
2 μm≦L≦100 μm, more preferably 1
0 μm≦L≦70 μm. If it is less than 2 μm, the initialization processing time will be long and productivity will be poor. If the thickness is larger than 100 μm, thermal deformation of the substrate and thermal distortion of the film are likely to occur.

The spot diameter of the two laser beams of the semiconductor laser 2.5 is
It may be a circular spot whose full width at half maximum is the same in the radial direction and the circumferential direction of the optical recording medium, or it may be a different elliptical spot, but especially when the spot diameter and light intensity of the laser beam are the same and the full width at half maximum is the same. It is preferable to use an elliptical spot that is long in the radial direction because the moving linear velocity can be increased, the initialization processing time is short, the optical system is simple, and the reflection level can be easily made uniform.

In the present invention, the shift width M of the optical axis of two laser beams having a specific full width at half maximum as described above in the direction perpendicular to the relative movement direction of the optical recording medium is L/4≦M≦7L.
It is important to synthesize with a shift within a range of /4.

The optical axis shift width Mμm needs to be from L/4μm to 7L/4μm, more preferably from 3L/4μm to
It is 3L/2μm. If it is less than L/4 μm, the light intensity is hardly different from a Gaussian distribution and the uniform area is narrow, so that the effect of the present invention is hardly obtained. 7L/4μ
If it is larger than m, the light intensity will drop considerably at the center, which tends to cause unevenness in the reflection level.

A method for shifting the optical axes of the two laser beams is, for example, a method of moving and arranging the semiconductor laser 2.5 parallel to the polarizing beam splitter 8 so as to shift the optical axis of the axis that has the maximum power in the light intensity distribution. , a method of changing the incident angle of the semiconductor laser 5 to the polarizing beam splitter 8, and a method of rotating the polarizing beam splitter 8 after aligning the optical axes of the semiconductor laser 2.5, but of course, the method is limited to these methods. Not done. Further, these methods may be used alone, but they can also be used in combination as appropriate.

Although the rotation of the optical recording medium can be set freely, it is preferable to keep the moving linear velocity constant in order to keep the laser beam irradiation time constant over the entire initialized portion of the disk.

If the linear velocity is slow, it will take a considerable amount of time to initialize the entire surface of the disk recording area, and in some cases, the film may be destroyed due to heat, while if the linear velocity is high, the surface runout of the optical recording medium will be large. Therefore, the linear velocity is 2m/S
A range of ~40 m/s is preferred.

Although the structure of the optical recording medium is not particularly limited, for example, a dielectric layer 1 is formed on a disk substrate 17 as shown in FIG.
8a1 recording layer 19 and dielectric layer 18b are provided in this order, and a reflective cooling layer 20 and a layer of 5 μm to 5 μm are further provided on the dielectric layer 18b.
Resin protective layer 2 such as an ultraviolet curable resin layer with a thickness of 40 μm
1 in this order is desirable because a more favorable effect can be expected by applying the initialization method of the present invention. Further, an adhesive layer may be provided on the protective layer 21 or may be bonded to another substrate.

When recording and erasing data from the substrate side, it is preferable to use a material that allows laser light to pass through the disk substrate, such as polymer resins such as polymethyl methacrylate resin, polycarbonate resin, epoxy resin, polyolefin resin, or glass. It will be done.

The dielectric layer is a deformation prevention layer that prevents the substrate and recording layer from being deformed by heat during recording and deterioration of recording and erasing characteristics, a protective layer that provides the recording layer with moist heat resistance and oxidation resistance, and a recording layer. It plays the role of an anti-diffusion layer that prevents atoms from diffusing from the reflective layer to the reflective layer. As such a dielectric layer,
For example, ZnS.

SiO2, Ta205. ITO, ZrC, TiC.

Inorganic films such as M g F 2 and mixed films thereof can be used. In particular, mixed films of ZnS and MgF2 and ZnS and 5i02 are preferable because they have excellent heat and humidity resistance and further suppress deterioration of the recording layer due to repeated recording and erasing.

The recording layer preferably has a fast crystallization rate as an optical recording medium, such as a Ge-8b-Te thin film, M-Ge-
8b-Te-based thin film (M is Pd, Cu, Ag, TI, Go
etc.), In-8b-Te based thin films, etc. In particular, when a Pd-Ge-8b-Te system thin film is initialized by the method of the present invention and its crystal structure transitions from an amorphous phase to a crystalline phase, it is a simple face-centered cubic film that requires less movement of atoms. It is preferable because it not only has a high crystallization rate because it has a structure and can be made into a single phase, but also is less likely to cause phase separation or compositional segregation even after repeated recording and erasing, and has excellent thermal stability.

The reflective cooling layer facilitates the formation of amorphous pits by facilitating heat diffusion from the dielectric layer and increasing the cooling rate of the recording layer melted during recording.

It also has the effect of preventing thermal deformation of the dielectric layer and the like, and the effect of improving the contrast of reproduced signals through optical interference. Such a reflective cooling layer can be made of metals, metal oxides, metal nitrides, metal carbides, etc. that have optical reflectivity and absorption at the wavelength of the laser beam and have higher thermal conductivity than the dielectric layer. mixtures of, e.g. Zr, Hf
, Ti, Ta, Mo, Si, AI, Au and other metals, their alloys, these Zr oxides, Si oxides,
A mixture of Si nitride, AI oxide, etc. can be used. In particular, materials such as AI, Au, Ta, and alloys thereof are preferred because they are easy to form a film and the thermal conductivity can be adjusted over a wide range by selecting the material.

The thickness of the dielectric layer, recording layer, and reflective cooling layer is 50 nm to 300 nm for the dielectric layer 18a, 10 nm to 30 nm for the dielectric layer 18b, and 10 nm to 60 nm for the recording layer.
It is preferable that the reflective cooling layer has a thickness of 20 nm to 1100 nm because an optical recording medium with good recording and erasing characteristics can be obtained.

Methods for forming the dielectric layer, recording layer, and reflective cooling layer on the disk substrate include known thin film forming methods in vacuum, such as vacuum evaporation, ion plate ink, and sputtering. . In particular, the sputtering method is preferred because the composition and film thickness can be easily controlled.

[Example] The following is a detailed explanation based on an example of the present invention.
The present invention is not limited thereto.

Note that the characteristics in the examples were evaluated based on the following method.

(1) Composition The compositions of the recording layer and dielectric layer were determined by determining the content of each element by ICP emission spectrometry (model FTS-1100, manufactured by Seiko Electronics Co., Ltd.), and calculating the composition ratio.

(2) Recording and erasing characteristics (1 beam override characteristics) The initialized optical recording medium was rotated at 9 m/s, and the recording power was modulated from the substrate side at a frequency of 5.3 MHz and a pulse width of 60 nS, with a recording power of 1 fmW and an erasing power of 9 mW. wavelength 780nm
Override recording was performed by condensing and irradiating semiconductor laser light using an objective lens with a numerical aperture of 0.5.

After recording, the recorded portion was scanned with a 1.3 mW semiconductor laser beam to reproduce the recording. Furthermore, the above recording frequency is
．． Changed to OMHz and performed override recording, 5.3M
After erasing the Hz recording signal, reproduction was performed under the same conditions as before. The carrier level and noise level of the recorded and erased reproduced signals were measured using a spectrum analyzer, the carrier-to-noise ratio (C/N) was determined under the condition of a bandwidth of 30 kHz, and the carrier level during recording at 5.3 MHz was determined. Level and 2, when recording OMHz (5,3M
The difference in carrier level at 5.3 MHz (when erasing Hz) was determined as the erasure rate.

(3) Reflection level after initialization The reflection level after initialization was determined using the same optical system used for measuring recording and erasing characteristics, and with a playback power of 1.3 mW.
The total reflection level was measured using an oscilloscope.

(4) Initialization state The initialization state was visually observed using a microscope.

Example 1 A recording layer, a dielectric layer, and a reflective cooling layer were formed by RF magnetron sputtering while rotating a polycarbonate substrate with spiral groups having a thickness of 1, 2 mm, a diameter of 130 mm, and a pitch of 1.6 μm at 600 revolutions per minute. did.

First, after exhausting to 7×10-5Pa, 6×10-'
ZnS and 5i0 were deposited on the substrate in an argon gas atmosphere of Pa.
ZnS-8i in a dielectric layer with a molar ratio of 2 to 80 + 20
02 with a thickness of 170 nm by sputtering method, then T
Pd2 was sputtered simultaneously while monitoring e, S b XT e, and Pd with a crystal resonator thickness meter
A recording layer with an elemental composition of Ge18Sb30Te50 is 25n
m was formed. Furthermore, ZnS-8i0 of the above dielectric layer
A 20 nm thick layer was formed thereon by a two-strip sputtering method, and 1100 nm of A1 alloy was formed thereon as a reflective cooling layer. Finally, A1
Apply ultraviolet curable resin on the layer using spin code method,
Thereafter, it was cured by irradiation with ultraviolet rays to form a 10 μm thick protective layer. As described above, an optical disc to which the initialization method of the present invention was applied was obtained.

Initialization is carried out using the apparatus shown in Fig. 1, in which the full width at half maximum in the radial direction of the optical recording medium is 22 μm, the circumferential direction is 66 μm, and the optical axis of the laser beam 2.5 with a power density of 0.5 mW/μrrf is set at 22 μm.
The experiment was performed using synchrotron radiation shifted by μm.

As a result, the rotation of the optical disc has a linear velocity of 2.0 to 6.0
Initialization can be performed at m/S, and the distribution of reflection levels in the initialized portion after one revolution of the optical disk becomes fairly uniform, and the entire optical disk can be initialized evenly and uniformly with a feed pitch of 20 μm or less. The recording and erasing properties of an optical disc whose entire surface was initialized under conditions that provided good recording and erasing properties at a linear velocity of 3.0 m/s and a feed pitch of 16 μm were evaluated using the previous evaluation method. As a result, the reflection level after initialization is uniform,
The initial C/N was 52.5 dB and the erasure rate was 30.2 dB, which were good C/N and erasure rates, and the initialization processing time was 3 minutes and 45 seconds, which was quite short.

Comparative Example 1 Initialization was carried out in the same manner as in Example 1 except that the optical axis was not slender.

As a result, the power density was doubled and the rotation of the optical disk was fast and the linear velocity could be initialized in the range of 5.5 to 10.0 m/s, but the distribution of reflection levels in the part initialized with one rotation of the optical disk was Since the peripheral portion is smaller than the central portion and the difference is thicker, the feeding pitch is considerably smaller than that in Example 1, and unless it is set to 4 μm or less, the entire optical disk cannot be initialized evenly and uniformly.

At a linear velocity of less than 5.5 m/s, the recording film was destroyed by heat. The recording and erasing properties of an optical disc whose entire surface was initialized under conditions that provided good recording and erasing properties, such as a linear velocity of 6.5 m/s and a feed pitch of 2 μm, were evaluated using the previous evaluation method. As a result, the reflection level after initialization was uniform, and a good C/N1 cancellation rate of 50.5 dEi and 29.6 dB was obtained for the initial C/N, but the initialization processing time was
It took a long time, 11 minutes and 35 seconds.

Comparative Example 2 Initialization was carried out in the same manner as in Example 1, except that the optical axis was shifted by 44 μm.

As a result, the rotation of the optical disk has a linear velocity of 2.0 to 5.0
m/s, which is not much different from Example 1, but the distribution of the reflection level in the initialized part during one revolution of the optical disk is smaller in the center than in the peripheral part, and the difference is wider, so the feeding pitch is as follows. It is smaller than 1, and unless it is 4 μm or less, the entire optical disk cannot be initialized evenly and uniformly. Conditions for obtaining good recording and erasing characteristics, linear velocity 4. Om/s,
The recording and erasing characteristics of an optical disk whose entire surface was initialized with a feed pitch of 2 μm were evaluated using the previous evaluation method.

As a result, the reflection level after initialization is uniform, the initial C/N is 51.0 dB, and the cancellation rate is 30.2 dB, which is a good C/N.
/N, the erasure rate was obtained, but the initialization processing time was 19 minutes 5
It takes 5 seconds, but it takes a lot of time and productivity is bad.

[Effects of the Invention] As described above, the present invention uses two specific laser beams combined under specific conditions, so that synchrotron radiation with significantly increased uniformity of light intensity distribution and temperature distribution can be obtained. Since initialization can be performed by irradiation, the optical recording medium can be uniformly crystallized. Furthermore, since the radial feed pitch and linear speed can be increased during initialization, initialization processing time can be considerably shortened and productivity can be increased.

[Brief explanation of drawings]

FIG. 1 shows one of the devices used to carry out the initialization method of the present invention.
FIG. 2 is an explanatory diagram showing an example of the structure of an optical recording medium. 1: Optical recording medium, 2, 5: Semiconductor laser, 3.6.13
: Laser light, 4.7: Collimator lens, 8: Polarizing beam splitter, 9: 1/2 wavelength plate, 10: Astigmatism correction lens, 1
6: Optical system, 17: Disk substrate, 18a, 18b: Dielectric layer, 19: Recording layer, 20: Reflective cooling layer, 21: Resin protective layer Fig. 1 Fig. 2

Claims (1)

[Claims] Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light, and information is recorded and erased by a phase change between an amorphous phase and a crystalline phase. When initializing the recording medium, two laser beams each having a full width at half maximum L of 2 μm≦L≦100 μm are used, and the shift width M of the optical axis in the direction perpendicular to the relative movement direction of the optical recording medium is set as L/ 4≦M≦7L/
4. A method for initializing an optical recording medium, characterized in that the recording layer of the optical recording medium is changed from an amorphous state to a crystalline state by irradiating the synthesized synchrotron radiation light shifted within a range of 4.