JPH11306606A - Manufacture of optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the amplitude of a recording signal and to obtain a stable recording/reproducing characteristic by specifying the sum of the content of a Ge atom and a Te atom incorporated in a recording layer, heating/melting the recording layer and making it a crystal state. SOLUTION: The regenerative signal amplitude is enlarged by incorporating the Ge atom in the recording layer by 30 atomic % or above, and a crystallization speed is adjusted by containing the Te atom and changing a composition ratio between the Ge atom and the Te atom. At this time, the sum of the content of the Ge atom and the Te atom is made an 80 atomic %, and a change in an erase rate at an initial overwrite time is suppressed to obtain the stable recording/reproducing characteristic. Further, the recording layer is heated to a melting point or above from an amorphous state just after a film is formed to be melted, and is cooled at a speed lower than a critical cooling speed to be crystalized and to be initialized. At the time, the necessity always melting the high melting point components in the recording layer excepting the Ge, Te atoms isn't eliminated within the range of not imparting a negative effect to a recording/erasing characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art The sum of the contents of Ge atoms and Te atoms is 80.
A recording layer having an atomic percentage or more is generally different from a recording layer used for a phase change recording medium in that the difference in optical properties (refractive index and extinction coefficient) between a crystalline phase and an amorphous phase is higher than that of Ge ₂ Sb ₂ Te _5. ), And the recorded signal has a large amplitude. For this reason, even when high-density recording (narrow track pitch, high linear density) is performed, a larger C / N
There is the advantage that a ratio can be obtained. That is, Ge atom and T
A recording layer having a total content of e atoms of 80 atomic percent or more has an advantage that high-density recording can be easily performed.

[0003]

However, an optical recording medium using a recording layer in which the sum of the content of Ge atoms and Te atoms is 80 atomic percent or more is not suitable for the first several to ten-odd overwrites. In addition, there is a problem that the erasing rate changes and stable recording / reproducing characteristics cannot be obtained.

An object of the present invention is to solve the above-mentioned problems and to provide an optical recording medium having a large amplitude of a recorded signal and having stable recording / reproducing characteristics from the first recording.

[0005]

According to the present invention, information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
A method for producing an optical recording medium, which is performed by a phase change between an amorphous phase and a crystalline phase of the recording layer, the method comprising:
An optical recording medium wherein the sum of the contents of atoms and Te atoms is 80 atomic percent or more, and the recording layer is changed from an amorphous state immediately after film formation to a crystalline state after being heated and melted; It is a manufacturing method of.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A conventional method for initializing a rewritable phase-change optical recording medium is as follows. A recording layer formed in an amorphous state on a substrate by a sputtering method or the like is coated with an Ar laser beam.
Irradiate semiconductor laser light, halogen lamp light, etc.,
Heat and crystallize (JP-A-2-5246)
According to the present invention, the recording layer is heated to a temperature equal to or higher than the melting point so that the recording layer is melted, and then cooled at a speed lower than the critical cooling rate, whereby the recording layer is changed to crystalline and initialized. As a method for heating the recording layer to a temperature equal to or higher than the melting point, there is a method in which the recording layer is irradiated with a laser beam and heated. At this time, when using a substrate that does not have high heat resistance,
It is important that the substrate not be thermally damaged. This can be achieved by irradiating low power DC light with a small spot diameter, but a method of irradiating high power pulse light with a large spot diameter can also be used as an advantageous method from the viewpoint of productivity. .

The state of the recording layer before the initialization according to the present invention may be either amorphous or crystalline, or a mixture thereof.

The composition of the recording layer of the present invention preferably contains 30 atomic% or more of Ge because the amplitude of the reproduced signal can be increased because the optical constants of the crystalline phase and the amorphous phase are significantly different.

In the recording layer of the present invention, the crystallization speed can be adjusted by changing the composition ratio of Ge atoms and Te atoms. Ge and Te are easy to adjust the composition ratio.
Preferably comprises only N, O, Pd, Ag,
In, Sb, Se, Pt, Au, Cu, Nb, Ga, P
It may contain a small amount of atoms such as b, Bi, V, W, Cr, Zr, and the like.

In the present invention, the high melting point component in the recording layer other than Ge and Te does not necessarily need to be melted at the time of initialization as long as the recording and erasing characteristics are not adversely affected.

The optical recording medium used in the present invention may be composed of only a recording layer formed on a substrate. However, in order to protect the recording layer and the substrate, the substrate, the first dielectric layer, the recording layer, It is preferable that two dielectric layers are provided in contact with the recording layer in the order of the dielectric layers. In addition, in order to obtain good recording / reproducing characteristics, a reflective layer or the like may be provided on the second dielectric layer. Further, each of the first dielectric layer and the second dielectric layer may be composed of two or more dielectric layers, and a metal having a light absorbing effect is provided between the second dielectric layer and the reflective layer. , A layer made of a semiconductor or the like may be provided.

The optical recording medium used in the present invention can be manufactured by the following method. Examples of a method for forming a recording layer, a dielectric layer, a metal layer, and the like on a substrate include a method of forming a thin film in a vacuum, such as a vacuum evaporation method, an ion plating method, and a sputtering method. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled. Control of the thickness of the recording layer to be formed
It can be easily performed by monitoring the deposition state with a quartz crystal film thickness meter or the like.

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

After the formation of the reflection layer, a dielectric layer such as ZnS, SiO ₂ , a mixture thereof, or a resin protective layer such as an ultraviolet-curing resin is formed as necessary to prevent scratches and deformation. It may be provided. After the formation of the reflection layer or the like, or after the formation of the above-mentioned resin protective layer, the two substrates may be opposed to each other and bonded with an adhesive. Further, a resin hard coat layer may be provided on the substrate surface on which the laser is incident, and this layer may be formed before the formation of the first dielectric layer or the like or after the formation of the reflection layer or the like.

The first and second dielectric layers of the present invention have an 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 deteriorating the recording characteristics. In addition, there is an effect that the signal contrast at the time of reproduction is improved by the optical interference effect.

The thickness d1 of the first dielectric layer is usually 50 nm or more and 400 nm or less because it is difficult to peel off from the substrate or the recording layer and hardly cause defects such as cracks. In order to increase the carrier-to-noise ratio (C / N) by increasing the contrast of the recording / reproducing signal, it is more preferable that d1
Is 0.25λ / wavelength λ of light used for recording and reproduction.
n1 ≦ d1 ≦ 0.70λ / n1. n1 is the real part of the refractive index of the first dielectric layer.

As the first dielectric layer and the second dielectric layer, there are inorganic thin films such as ZnS, SiO ₂ , silicon nitride, and aluminum oxide. Especially ZnS thin film, Si, G
e, a thin film of a metal oxide such as Al, Ti, Zr, Ta, and Ce; a thin film of a nitride such as Si and Al;
A thin film of a carbide such as Hf and a film of a mixture of these compounds are preferable because of high heat resistance. Further, those obtained by mixing carbon or a fluoride such as MgF _{2 with} these are also preferable because the residual stress of the film is small. Especially ZnS and S
A mixed film of iO ₂ or a mixed film of ZnS, SiO ₂ and carbon has a recording sensitivity and C
/ N, the erasure ratio, etc. are less likely to occur, and a mixed film of ZnS, SiO ₂ and carbon is particularly preferable.
The molar ratio between ZnS and SiO ₂ is ZnS / SiO ₂ = 85/1.
A 5~65 / 35, (ZnS + SiO 2) and C molar ratio of _{(ZnS + SiO 2) / C} = 99 / 1~80 / 2
It is preferably 0.

The reflective layer has two effects, that is, an effect of releasing heat generated in the recording layer during initialization and recording, and an effect of improving reproduction signal characteristics due to optical interference.

As a material of the reflection layer, a metal such as Al or Au having light reflectivity, or a material containing these as a main component,
Alloys containing additional elements such as i, Cr, Hf and Al, A
Examples thereof include a mixture of a metal such as u and a metal compound such as a metal nitride such as Al and Si, a metal oxide, and a metal chalcogenide. 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 above-mentioned alloy, Al, Si, Mg, Cu, Pd, Ti, Cr, H
At least one element such as f, Ta, Nb, Mn or the like added in a total of 5 at% or less and 1 at% or more, or at least one of Au, Cr, Ag, Cu, Pd, Pt, Ni, etc. Element total 20 atomic% or less 1 atomic%
These are the ones added above. Particularly, an alloy containing Al as a main component is preferable because the price of the material can be reduced.
at least one metal selected from the group consisting of r, Ta, Hf, Zr, Mn, and Pd in a total of 5 atomic% or less and 0.5 atomic%.
The alloys added above are preferred. In particular, because corrosion resistance is good and hillocks do not easily occur,
Al-Hf-Pd alloy, Al-Hf alloy, Al containing a reflective layer containing a total of 0.5 to 3 atomic% of additional elements
-Ti alloy, Al-Ti-Hf alloy, Al-Cr alloy,
Al-Ta alloy, Al-Ti-Cr alloy, Al-Si-
It is preferable to use any one of the Mn alloys mainly containing Al.

As the material of the substrate of the present invention, various transparent synthetic resins, transparent glass and the like can be used. In order to avoid the influence of dust and scratches on the substrate, it is preferable to use a transparent substrate and perform recording from the substrate side with a focused light beam.As such a transparent substrate material, 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.

The thickness of the substrate is not particularly limited, but is practically 0.01 mm to 5 mm. 0.01m
If it is less than m, even when recording with a light beam focused from the substrate side, it is easily affected by dust, and if it is 5 mm or more,
It becomes difficult to increase the numerical aperture of the objective lens, and the spot size of the irradiation light beam becomes large, so that it becomes difficult to increase the recording density. 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 using two substrates after forming a recording layer or the like.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (Analysis and Measurement Method) The compositions of the reflective layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Instruments Inc.).
The film thickness during the formation of the recording layer, the dielectric layer, and the reflective layer was monitored with a quartz crystal film thickness meter. The thickness of each layer was measured by observing the cross section with a scanning or transmission electron microscope.

The measurement of the erasing rate is performed by first using an optical head having a numerical aperture of an objective lens of 0.6 and a wavelength of 680 nm of a semiconductor laser on a groove under a condition of a linear velocity of 6 m / sec.
A signal of 4.8 MHz (duty 40%) was recorded. At this time, the recording power and the erasing power were set to optimal values for each disk. Here, once the carrier of this signal is measured using a spectrum analyzer and the bandwidth is 30
It was measured under the condition of KHz. Next, the power of the semiconductor laser is set to the optimum erasing power for each disk.
Trace was performed only once while irradiating C (hereinafter referred to as DC erase). Then, the remaining carrier of the signal was measured. The above-described difference between the carrier at the time of recording and the remaining carrier was defined as a DC erase ratio.

(Example 1) Thickness 0.6 mm, diameter 12c
Sputtering was performed while rotating a polycarbonate substrate with spiral grooves having a pitch of m, 1.2 μm (land width 0.6 μm, groove width 0.6 μm) at 30 revolutions per minute.

First, the inside of the vacuum vessel is evacuated to 1 × 10 ^-3 Pa, and then SiO 2 is evacuated in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
ZnS to which 20 mol% of ₂ was added was sputtered to form a first dielectric layer having a thickness of 105 nm on the substrate. continue,
Sputtering a target made of GeTe to a thickness of 20
A recording layer having a composition of Ge _50.0 Sb _50.0 nm was obtained. Furthermore, the same ZnS.SiO ₂ as the first dielectric layer is used as the second dielectric layer.
Is sputtered to form a 16 nm layer, on which AlHf
A Pd alloy was sputtered to form a reflective layer having a thickness of 150 nm, and an optical recording medium of the present invention was obtained.

After the sputtering, a protective coat was applied to the sputtered surface of the recording medium. In this state, the recording layer is still in an amorphous state.

The obtained disk was placed on an optical disk drive, and DC irradiation was first performed only once with a laser power of 11.5 mW to heat and temporarily melt the recording layer.
Thereafter, the same track was subjected to DC irradiation only once with a laser power of 6.5 mW to crystallize the recording layer of the track.

Thereafter, the recording power / erasing power is set to 11.
The above signal was recorded only once at 5 / 6.5 mW, and the C / N was measured. As a result, a necessary and sufficient value of 57 dB was obtained. Further, this part is DC-erased and its D
When the C erase ratio was measured, a necessary and sufficient DC erase ratio of 27 dB could be obtained.

Example 2 In the same manner as in Example 1, when sputtering the recording layer, pellets of Sb ₂ Te ₃ were placed on a target made of GeTe, and the composition was Ge ₄₀ Sb _8.
To obtain a recording layer composed of Te _52.

The same initialization process as in Example 1 was performed and the measurement was performed.
A DC erasing ratio of 8 dB was obtained.

Comparative Example 1 A disk was obtained in the same manner as in Example 1 except for the steps up to the protective coating. The obtained disk is placed on an optical disk drive and the laser power is 6.5.
DC irradiation was performed only once at mW to crystallize the recording layer of the track without melting the recording layer.

Thereafter, the recording power / erasing power is set to 11.
The above signal was recorded only once at 5 / 6.5 mW, and the C / N was measured. As a result, a C / N of 57 dB was obtained. However, when DC erasing was performed and the DC erasing ratio was measured, the DC erasing ratio was found to be as low as 14 dB, which was not suitable for practical use.

Comparative Example 2 A disk was obtained in the same manner as in Example 1 except for the steps up to the protective coating. The obtained optical disk was subjected to a laser wavelength of 830 nm and a beam diameter of 0.85 × 55.
The recording layer on the entire surface was crystallized and initialized by irradiating DC light using an initialization device having an optical head of μm. During this initialization, the recording layer does not melt once.

When the C / N and DC erasure ratio of this disk were measured in the same manner as in Comparative Example 1, a value of 57 dB was obtained for the C / N, but the DC erasure ratio was as low as 13 dB, which was suitable for practical use. I knew it wasn't.

Comparative Example 3 A disk was obtained in the same manner as in Example 2 up to the step of protective coating. Initialization was performed in the same manner as in Comparative Example 2, and the C / N and DC erase ratio were measured. C / N
Was 56 dB, but the DC erasure ratio was measured to be as low as 15 dB, which proved to be unsuitable for practical use.

Comparative Example 4 The composition of the recording layer was Ge ₂ Sb ₂ T
except that the e _5, thereby obtaining the disks in the same manner as in Example 1. In the initialization, DC irradiation was performed only once with a laser power of 10.5 mW, and the recording layer was heated and once melted.
Thereafter, the same track was subjected to DC irradiation only once at a laser power of 4.5 mW, and initialization was performed in the same manner as in Example 1 except that the recording layer of the track was crystallized.

Thereafter, the recording power / erasing power is set to 10.
The above signal was recorded only once at a setting of 5 / 4.5 mW, and the C / N was measured. As a result, it was found to be as small as 51 dB, which was not suitable for practical use.

[0038]

According to the method for initializing an optical recording medium of the present invention, the following effects are obtained. The amplitude of the recorded signal was large, and a high erasing rate could be stably obtained from the first recording to the overwriting several to ten and several times.

Claims (4)

[Claims] A recording layer formed on a substrate is irradiated with light so that information can be recorded, erased, and reproduced. The recording and erasing of information can be performed in an amorphous phase and a crystalline phase of the recording layer. Wherein the sum of the contents of Ge atoms and Te atoms in the recording layer is 80 atomic percent or more, and the recording layer is formed immediately after film formation. A method for producing an optical recording medium, wherein the method changes from an amorphous state to a crystalline state after heating and melting. 2. The method according to claim 1, wherein the recording layer contains at least 30 atomic percent of Ge. 3. The method for manufacturing an optical recording medium according to claim 1, wherein the optical recording medium has a structure in which at least a first dielectric layer, a recording layer, and a second dielectric layer are laminated in this order on a transparent substrate. 4. The method of manufacturing an optical recording medium according to claim 1, wherein the optical recording medium has a structure in which at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are laminated in this order on a transparent substrate. Method.