JP2000182286A - Manufacture of optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase change optical recording medium which has excellent high-density preservation durability by improving erasability in wet-hot preservation and preservation in initial recording which are important for the high density recording. SOLUTION: When the optical recording medium is manufactured in which medium information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with a light beam and is recorded and erased by phase change between an amorphous phase and a crystal phase, the recording layer is manufactured by sputtering and sputtering gas contains at least hydrogen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to
The present invention relates to a method for manufacturing an optical information recording medium capable of recording, erasing, and reproducing information. In particular, the present invention relates to a method for manufacturing a rewritable phase-change optical recording medium such as an optical disk having an erasing and rewriting function of recorded information and capable of recording an information signal at high speed and high density. is there.

[0002]

2. Description of the Related Art The technique of a conventional method for manufacturing a rewritable phase-change optical recording medium is as follows.

When manufacturing an optical recording medium, each layer including the recording layer constituting the medium is often formed by a sputtering method. In this case, a rare gas such as argon is often used as a sputtering gas because it is inexpensive and does not affect the composition of the constituent layers. On the other hand, it is desired to improve the erasing characteristics of optical recording media for long-term storage. To solve this problem,
For example, Japanese Patent Application Laid-Open No. 9-286176 discloses that a gas obtained by mixing nitrogen with argon is used as a sputtering gas.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the erasing characteristics during long-term storage corresponding to the high density of a phase change recording medium. Another object is to improve the erasing characteristics for the first-time write mark on the portion where the operation has been performed.

[0005]

Means for Solving the Problems To solve the above problems, the present invention comprises the following constitutions. That is, by irradiating a recording layer formed on a substrate with a red laser, information can be recorded, erased, and reproduced. Information recording and erasing can be performed by a phase change between an amorphous phase and a crystalline phase. A method for producing an optical recording medium for red laser, characterized in that when producing an optical recording medium for red laser, the recording layer is produced by a sputtering method, and the sputtering gas contains at least hydrogen. Here, the red laser refers to a laser having a wavelength of 600 nm or more. As an invention having a configuration similar to the present invention, Japanese Patent Application Laid-Open No. 10-208296 discloses an example in which sputtering is performed using a gas obtained by mixing hydrogen with argon, which has a wavelength of 400 to 500 nm. It is limited to the phase change type information recording medium for short wavelength laser having the following, and the prerequisite technology is different from the present invention.

[0006] By performing sputtering using a sputtering gas containing hydrogen, the erasing operation of the phase change recording film, that is, the crystallization from the amorphous phase can be easily performed, and its characteristic can be obtained even during long-term storage durability. Will not be lost.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical layer structure of a constituent member of an optical recording medium according to the present invention is, for example, a laminate of a transparent substrate / first dielectric layer / recording layer / second dielectric layer / reflective layer. Is constituted as a member, but is not limited thereto.

In the present invention, the term “substrate” is not particularly limited. On a transparent substrate, recording can be performed from the substrate side with a converged light beam, and the effects of dust and scratches on the substrate can be avoided. Therefore, it can be preferably used. For example, various transparent synthetic resins and transparent glass can be used. Such transparent substrates include glass, polycarbonate, polymethyl methacrylate,
Polyolefin resin, epoxy resin, polyimide resin and the like can be mentioned. In particular, a polycarbonate resin and an amorphous polyolefin resin are preferable because they have low optical birefringence, low hygroscopicity, and are easy to mold.
When heat resistance is required, an epoxy resin is preferred.

The substrate may be flexible or rigid. The flexible substrate is used in the form of a tape, a sheet, or a card. The rigid substrate is used in the form of a card or a disk. In addition, these substrates may be formed into an air sandwich structure, an air incident structure, or a close bonding structure by using two substrates after forming a recording layer or the like.

The thickness of the substrate is not particularly limited, but is practically 0.01 mm or more and 5 mm or less. 0.01
mm or less makes it less susceptible to dust.
When the diameter is equal to or less than mm, the numerical aperture of the objective lens can be easily increased, and the spot size of the irradiation light beam can be reduced, so that the recording density can be easily increased.

In the present invention, the dielectric layer has the effect of protecting the substrate and the recording layer from heat, such as preventing the substrate and the recording layer from being deformed by heat during recording and thereby deteriorating the recording characteristics, and the optical interference effect. This has the effect of improving the signal contrast during reproduction. As this dielectric layer, Zn
Inorganic thin films such as S, SiO ₂ , silicon nitride, and aluminum oxide can be used. Especially ZnS thin film, Si, G
e, thin films of oxides of metals such as Al, Ti, Zr, Ta, etc., thin films of nitrides such as Si, Al, Ti, Zr, Hf
Carbide thin films and films of these compounds are preferred because of their high heat resistance. The refractive index of these thin films is 1.5 or more and 2.4 or less. Further, those obtained by mixing carbon or a fluoride such as MgF _{2 with} these are also preferably used because the residual stress of the film is small. Especially Zn
A mixed film of S and SiO ₂ , or a mixed film of ZnS, SiO ₂ and carbon can be used for recording sensitivity, carrier-to-noise ratio (C / N) and erasing rate (after recording and after erasing) even by repeating recording and erasing. This is preferable because deterioration such as a difference in reproduced carrier signal strength) hardly occurs. Although the composition ratio of the chalcogen compound, the oxide and the carbon is not particularly limited, SiO ₂ 15
More preferably, it is from about 35 mol% to 1 mol% of carbon.

The thickness of the first dielectric layer is determined by optical conditions, but is usually about 50 nm to 500 nm. The thickness is preferably 50 nm to 400 nm because it is hard to peel off from the substrate or the recording layer and hardly causes defects such as cracks.
In particular, since the difference in the amount of light absorption between the amorphous state and the crystalline state of the recording layer can be reduced, it is desirable that the thickness of the first dielectric layer be set to satisfy the following expression.

Nλ / 4−0.2λ <nd1 <Nλ / 4 + 0.2λ, where N is an integer selected from 1, 3, and 5, λ is the wavelength used for recording, and n is the first dielectric. The refractive index (real part) of the layer, d1, is the thickness of the first dielectric layer.

In the present invention, the recording layer means a layer made of a material capable of repeating a phase change between a crystalline phase and an amorphous phase by irradiation with a red laser. For example, there is a method in which a phase change between a crystalline phase and an amorphous phase is repeated by the following method. That is, during information recording, a concentrated red laser light pulse is irradiated for a short time to partially melt the recording layer. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. In addition, at the time of erasing, the recording mark portion is irradiated with a red laser beam and heated to a temperature below the melting point of the recording layer and above the crystallization temperature to crystallize the amorphous recording mark,
Return to the original unrecorded state.

The composition and composition of the material of the recording layer are not particularly limited, but include a Pd-Ge-Sb-Te alloy, an Nb-Ge-S
b-Te alloy, Pd-Nb-Ge-Sb-Te alloy, Ni-Ge-Sb-Te alloy, Ge-
Sb-Te alloy, Co-Ge-Sb-Te alloy, In-Sb-Te alloy, Ag-In-Sb
-Te alloy, In-Se alloy and the like. In particular, Pd-Ge-Sb-Te alloys, Nb-Ge-Sb-Te alloys, and Pd-Nb-Ge-Sb-Te alloys have a short erasing time and are capable of repeating recording and erasing many times. / N, and excellent recording characteristics such as erasing ratio, and particularly, a Pd-Nb-Ge-Sb-Te alloy is preferable because of its excellent characteristics.

The thickness of the recording layer is preferably from 10 nm to 30 nm. By setting the thickness of the recording layer to 10 nm or more, deterioration of recording characteristics due to repeated overwriting can be suppressed, and by setting the thickness of the recording layer to 30 nm or less, movement of the recording layer due to repeated overwriting. Is less likely to occur and the jitter can be reduced. In particular, the recording and erasing sensitivity is high, recording and erasing can be performed many times, and the recording mark shape becomes uniform.

The thickness of the second dielectric layer is 1 nm or more and 50 n
m or less is preferable because deterioration due to repetition of recording rewriting is small. Considering the durability and the degree of cooling of the recording layer at the time of recording, it is preferably 5 nm or more, and the degree of cooling of the recording layer at the time of recording erasure and the light absorption of the amorphous state are larger than the light absorption of the crystalline state. Considering that it does not occur, it is preferably 40 nm or less.

The reflective layer in the present invention is not particularly limited, but examples thereof include light-reflective metals, alloys, and mixtures of metals and metal compounds. As the metal, Al, Au, Ag, a metal with a high reflectance such as Ag, Cu, and as an alloy, an alloy containing the above metal as a main component and containing at least 80 atomic% and containing additional elements such as Ti, Te, Cr, and Hf; As metal compounds, metal nitrides such as Al and Si,
Metal compounds such as metal oxides and metal chalcogenides are preferred. Metals such as Al and Au and alloys containing these as main components are preferable because of their high light reflectivity and high thermal conductivity. As an example of the aforementioned alloy, Al, Si, Mg,
At least one element such as Cu, Pd, Ti, Cr, Hf, Ta, Nb, and Mn, in which a total of 5 atomic% or less and 0.5 atomic% or more are added, or Au is added to Cr, Ag, Cu, There is a material in which at least one element such as Pd, Pt, and Ni is added in a total amount of 20 atomic% or less and 1 atomic% or more. In particular, an alloy containing Al as a main component is preferable because the material can be processed at low cost. In particular, as an Al alloy, because of its good corrosion resistance,
An alloy in which at least one metal selected from Ti, Cr, Ta, Hf, Zr, Mn, and Pd is added in a total amount of at least 0.5 atomic% or less, or a total of 5 atomic% or less in Al With Si
An alloy containing Mn is preferred. In particular, since the recording layer has high corrosion resistance and high thermal stability and hillocks hardly occur in the recording layer, the reflective layer contains the additive element in a total of less than 3 atomic% and 0.5 atomic% or more. Pd alloy, Al-Hf alloy, Al-Ti alloy, Al
-Ti-Hf alloy, Al-Cr alloy, Al-Ta alloy, Al-Ti-Cr alloy, Al
It is preferable to be composed of any of the -Si-Mn alloys mainly containing Al.

The thickness of the reflective layer is not particularly limited as long as sufficient reflective characteristics can be obtained and at the same time it is sufficient to have a sufficient heat radiation effect to rapidly diffuse excess heat generated in the recording film. In the example of the Al alloy described above, 30 nm to 2 nm
It may be in the range of 00 nm.

The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as a laser beam or a strobe light.
It is preferable because power consumption is small and modulation is easy.

The recording is performed by irradiating a recording layer in a crystalline state with a laser beam pulse or the like to form an amorphous recording mark. Alternatively, a recording mark in a crystalline state may be formed on a recording layer in an amorphous state. The erasing can be performed by crystallizing an amorphous recording mark by laser beam irradiation or by amorphizing a crystalline recording mark.
Since the recording speed can be increased and the recording layer is hardly deformed, it is preferable to form an amorphous recording mark at the time of recording and crystallize at the time of erasing.

When forming a recording mark, the light intensity is high.
The one-beam overwriting method, in which erasing is slightly weakened and rewriting is performed by one light beam irradiation, is preferable because the time required for rewriting is reduced. Also, for the purpose of improving the jitter characteristics of recording marks, recording compensation such as a so-called off-pulse method, which is a recording method for rapidly decreasing the light intensity immediately after increasing the light intensity at the time of forming the recording mark, is generally known. However, it is also preferable to appropriately specify such a recording method.

Next, a method for manufacturing an optical recording medium according to the present invention will be described.

In the present invention, a sputtering method is used as a method for forming a recording layer or the like on a substrate because the composition and the film thickness can be easily controlled. Further, a sputtering gas containing at least hydrogen is used. If the sputtering gas does not contain hydrogen, the effect of improving the erasing characteristics during long-term storage and the effect of improving the erasing characteristics during initial writing cannot be obtained. The composition of the sputtering gas is preferably a mixed gas of a rare gas and hydrogen so as not to cause an unnecessary reaction with the composition of the recording layer, and more preferably a mixed gas of argon and hydrogen from the viewpoint of cost. Also,
The ratio of the partial pressure of hydrogen to the total pressure of the sputtering gas is preferably 0.5% to 5%. When the content is 0.5% or more, the effect of including hydrogen in the sputtering gas is obtained, and when the content is 5% or less, the gas tends to be easily and safely handled.

The formation of the recording layer and the like may be performed while the substrate is fixed, or moved or rotated. The substrate is preferably rotated on its own axis because of excellent in-plane uniformity of the film thickness, and more preferably combined with revolution.

[0026]

The present invention will be described below with reference to examples. However, the present invention is not limited by the following examples.

The composition of the dielectric layer, the recording layer and the reflection layer is determined by the ICP
It was confirmed by emission analysis (manufactured by Seiko Denshi Kogyo KK). Further, the C / N and the erasing rate (difference in the intensity of the reproduced carrier signal after recording and after erasing) were measured by a spectrum analyzer. The cross erasure characteristics were also measured using a spectrum analyzer.

(Example 1) Thickness 0.6 mm, diameter 120 m
A phase change recording medium was produced by a high-frequency sputtering method while rotating a polycarbonate substrate with spiral grooves of m, 1.2 μm pitch (land 0.6 μm, groove 0.6 μm) and groove depth 71 nm at 40 rpm.

Firstly, after evacuating the vacuum vessel to ^{1 × 10 -5 Pa, 2 ×} 10 -1 Pa of Ar gas atmosphere (Ar 20.0 ccm (25
(Ar gas of 20.0 cm ³ was flowed per minute in terms of 1.013 × 10 ⁵ Pa).) ZnS containing 20 mol% of SiO ₂ was sputtered in) to form a first dielectric layer having a thickness of 90 nm. . Next, in a mixed gas atmosphere (Ar 19.2 ccm, H2 0.8 ccm, partial pressures 96.0% and 4.0%, respectively), an alloy target composed of Pd, Ge, Sb, and Te was sputtered with DC, and Pd0 A recording layer of .2Ge19.4Sb24.2Te56.4 (atomic%) with a thickness of 17 nm was formed. Further, a second dielectric layer of the same material as that of the first dielectric layer was formed to a thickness of 22 nm, and a reflective layer having a thickness of 120 nm was formed thereon. The material of the reflective layer was Hf0.02Pd0.002Al0.978.

Further, after taking out the optical recording medium from the vacuum container, an acrylic ultraviolet curable resin was spin-coated and cured by irradiation with ultraviolet light to form a resin layer having a thickness of 10 μm. Thereafter, initialization was performed by a bulk eraser (manufactured by Shibasoku Co., Ltd.), and the recording layer was crystallized. Further, the optical recording medium of the present invention was obtained by laminating an optical recording medium having the same configuration with an ultraviolet curable adhesive.

These optical recording media were converted to a linear velocity of 5.5 m / s.
(At a radius of 40 mm at a rotational speed of about 1300 rpm), the numerical aperture of the objective lens is 0.6, and the wavelength of the semiconductor laser is 6
An experiment for evaluating the recording and erasing characteristics was performed using an optical head of 80 nm. At this time, when the beam spot diameter was measured by the knife edge method, it was a perfect circle of 0.94 μmφ. The signal modulation system used was (1-7) RLL. First, the 8T signal is converted to a frequency of 1.88 MHz (signal duty = 50%).
After overwriting 100 times with a semiconductor laser beam modulated under the conditions of a peak power of 7.5 mW and a bottom power of 3 to 5 mW, a 7.5 MHz 2T signal is overwritten once and an 8T recording signal is overwritten. The erasure rate was measured. The erasing rate was defined by the amount of carrier change before and after 2T overwriting of the 8T signal.

A similar experiment was performed even if the number of recordings of the 8T signal was one.

Further, an experiment in which the 8T signal was recorded 100 times and once, and then stored in an environment of 90 ° C. and 80% RH for 60 hours, cooled, and then the 2T signal was overwritten once. (This is referred to as the "moist heat test"). As a result of performing the disk evaluation according to the above-mentioned index, the results shown in the following table were obtained. Before moist heat test 100
The erasure rate at the time of the other three recordings is not so bad as compared with the time of the first recording, and the erasing characteristics at the time of the single recording and the durability of the erasing characteristics with respect to the wet heat test are not likely to deteriorate. I understand.

(Example 2) An optical recording medium was produced in the same manner as in Example 1 except that the partial pressure of the sputtering gas for producing the recording layer was 99.0% for Ar and 1.0% for H2.
When evaluation was performed in the same manner as in Example 1, the results shown in the following table were obtained. Although 20% lower than that of Example 1, required 20 dB as erasing characteristics could be obtained.

(Comparative Example 1) An optical recording medium was produced in the same manner as in Example 1 except that the sputtering gas used for producing the recording layer was also 100% Ar. When evaluation was performed in the same manner as in Example 1, the results shown in the following table were obtained. The erasure rate during the other three recordings was very poor compared to the 100 recordings before the wet heat test, and the necessary 20 dB as the erasing characteristics could not be obtained.

[0036]

[Table 1]

[0037]

According to the present invention, in a phase change recording medium, light having improved erasing characteristics during wet heat storage and storage during initial recording, which are problems at the time of high density recording, and excellent in high density storage durability are obtained. A recording medium can be provided.

Claims (3)

[Claims] 1. A recording layer formed on a substrate is irradiated with a red laser to record, erase, and reproduce information. The recording and erasing of information can be performed by using an amorphous phase and a crystalline phase of the recording layer. When producing an optical recording medium for red laser performed by a phase change between, the recording layer is produced by a sputtering method, and the sputtering gas contains at least hydrogen of the optical recording medium for red laser Production method. 2. The method according to claim 1, wherein the sputtering gas contains argon. 3. The method according to claim 1, wherein the ratio of the partial pressure of hydrogen to the total pressure of the sputtering gas is 0.5% to 5%.