JPH0430343A - Protective film for optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the performance of a disk by repetition of recording and erasing by producing hydrogen-contg. SiN protective layers provided on both sides of a thin-film recording layer by using an ECR plasma CVD method. CONSTITUTION:The material of the protective films for the optical recording medium formed with the protective films on both sides of the thin-film recording layer of the optical recording medium by using the electron cyclotron resonance (ECR) plasma CVD method consists of SixNi1-x (0.4<=X<=0.6) and contains hydrogen in a 1X10<22> to 4X10<22> atoms/cm<3> range. The thermal conductivity is lowered by increasing he hydrogen content in such a manner and the a-SiN:H film having the high adhesive strength and small internal stress is formed.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a protective film for an optical recording medium that records and erases information by irradiating a laser beam and causing an optical change in the irradiated area. be.

(Prior art) Recently, rewritable optical disks, which record and erase information by irradiating a thin film-like medium on a substrate with a focused laser beam to cause optical changes in the thin film, have been developed for high-density, large-capacity storage. It is attracting attention as a new technology that makes it possible. These rewritable optical disks include magneto-optical disks and phase change optical disks. Magneto-optical disks use the magnetic Kerr effect to
Information is recorded and erased by rotating the polarization plane of laser light.

On the other hand, phase-change optical disks perform recording by heating and rapidly cooling a thin film-like optical recording medium above its melting point with a laser beam, making the portion irradiated with the laser amorphous. By heating and annealing the material to a temperature higher than the crystallization temperature, the material is returned to a crystalline state and erased.

The front and back surfaces of this phase change optical disk thin film recording layer have the effect of preventing deformation of the recording layer and optically enhancing it.
A transparent dielectric protective film is added.

Recently, in order to further enhance the enthroning effect, many have added a metal reflective layer to the top layer. The material of the protective film is SiO□, ZnS, or SiN.

etc. are conventionally used, and are usually produced by vapor deposition or sputtering.

Until now, development efforts have focused on improving the characteristics of the recording film itself, such as increasing erasing speed and data storage life, for the characteristics of phase-change optical disks. Recently, 1
A recording film that is capable of high-speed erasing of 00 ns or less and has a data storage life of 10 years or more has been obtained, and so-called 1-beam override has also been realized. Therefore, the focus of development has shifted to improving recording sensitivity and repeat durability, and the optimization of the medium construction method of phase change optical disks, in particular the dielectric protective film, is becoming a major issue.

Although recording sensitivity and repetition characteristics strongly depend on the material of the dielectric protective film, no firm guidelines have been obtained regarding the effects of differences in the material and manufacturing method of the protective film on the characteristics of optical discs. The current situation is that there is no such thing.

It goes without saying that magneto-optical disks also require a dielectric protective film to protect the recording film and enhance the Kerr effect.

Listing the drawbacks of the protective film of conventional phase change optical disks, they are as follows:
It is as follows.

(2) When a dielectric protective film is formed by sputtering or vapor deposition, the film deposition rate is low, so the deposition time is long, which becomes a rate-limiting factor in the production of optical disks.

■ If the residual film stress in the protective film is large, or if the adhesion between the protective film and the recording film or between the recording film and the substrate is weak, repeated erasing of records will induce irreversible deformation and will be destroyed after about 104 times. There were many cases where the characteristics deteriorated.

■ In order to improve the recording and erasing repetition characteristics, for example, literature (Ohta et al.; Jpnj, Appl.
, Phys, 28° (1989), 5upp1.28
-3. As seen in pp. 123-128), when a medium with a quenching structure is used, recording sensitivity decreases and recording power becomes insufficient during high-speed rotation.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned drawbacks of the protective film for optical discs, and provides protection for highly sensitive optical recording media that can prevent deterioration of disc performance due to repeated recording and erasing. The goal is to provide a membrane.

(Means for Solving the Problems) In order to achieve the above problems, the present inventors aimed at phase change optical disks,
-202918, electron cyclotron resonance (E
CR) We have devised a method for manufacturing a protective film using chemical vapor deposition (CVD) using plasma, and have shown that it is possible to create a phase-change optical disk that exhibits excellent repeatability and recording sensitivity.

In other words, in ECR plasma, conventional RF plasma (1
Compared to 3,56M1(z), there are a large number of circularly moving high-energy electrons, so a plasma with high activity (decomposition/excitation) and high ionization rate is stable at a low gas pressure of about 10'-'Torr. It has the characteristic that it can be generated.

Therefore, ■ The decomposition of the reactive gas is carried out efficiently, allowing for high-speed deposition (high-speed deposition of protective films for optical disks); ■ Ion bombardment that does not damage the substrate has the effect of accelerating the film formation reaction. It is possible to form a dense, high-quality thin film with strong adhesion without heating the substrate (a protective film for optical disks with a good protective effect can be realized using a low-temperature process that can also be applied to PC boards). ■ Unlike the sputtering method, the gas is dissociated by plasma and a thin film is formed by a gas phase reaction, so the reaction gas flow rate,
The quality of the film largely depends on the production conditions such as reaction gas ratio and input power. For example, the film stress can control bacteria over a wide range of compressive force = stress free - tensile stress (realization of a protective film with high repeated durability). ■ H atoms generated by the dissociation of SiH4 gas are mixed into the resulting thin 7 film, so the thin film contains hydrogen, and the thermal conductivity of the film can be changed by the difference in hydrogen content ( This has the effect of improving recording sensitivity by utilizing the decrease in thermal conductivity due to hydrogen content.

These effects make it possible to provide a thin film that is optimal as a protective film for optical disks, which could not be obtained by conventional sputtering or RF plasma CVD methods.

The present invention proposes a method of forming an a-3iN:H film with low thermal conductivity, strong adhesion, and low internal stress by increasing the hydrogen content, and using this thin film. This demonstrates that high recording sensitivity and high repeatability can be achieved simultaneously.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

Embodiment 1 FIG. 1 is a diagram for explaining one embodiment of the present invention.
The relationship between hydrogen content and recording sensitivity of a SiN thin film formed by R plasma CVD method is shown. The media configuration of the optical disc used was PC (polycarbonate) grooved substrate/SIN
SiN undercoat layer - Te-based recording layer/SiN overcoat layer/Au metal reflective layer/epoxy resin layer for sealing. The recording layer and the metal reflective layer were formed by RF sputtering, and both had a film thickness of 40 nm. The epoxy resin layer for sealing was prepared by spinner coating and had a thickness of about 10 μm.

The SiN undercoat layer is 1100nm thick, the SiN overcoat layer is 200nm thick, and ECR plasma CV
It was produced by method D. The hydrogen content of the protective film (SiN undercoat, overcoat) was determined by fixing the microwave power to 500W and setting the reaction gas ratio to 5IH4:
Bacterial control was achieved by changing the total flow rate of the reaction gas while keeping N2=l:3 constant. Table 1 shows the relationship between manufacturing conditions and hydrogen content.

From FIG. 1, it can be seen that the recording sensitivity improves as the hydrogen content increases. Hydrogen content 3.20X 1022H
When using a protective film of atoms/cm3, the linear speed is 10 m
/s.

Under recording conditions of 5 MHz (50 ns), a C/N value of 52 dB or more was obtained at 11 mw. Since the recording sensitivity of a conventional phase change optical disk (sputtered SiN protective film containing no hydrogen in Table 1) is approximately 17 to 18 mW under the same recording conditions, the present invention makes it possible to create a medium with excellent recording sensitivity. I understand.

Next, FIG. 2 shows the repeated recording/erasing characteristics of this highly sensitive phase change optical disk with a recording sensitivity of 11 mW.

The measurement was performed at a linear velocity of 10 m/s and a recording condition of 5 MHz (50 ns
) -11mw15.5mw (recording power/base erasing power) override mode was performed. From the top of the diagram, each of the recording level, erasing level, and noise level is d.
BDisplay and show.

From this, it can be seen that the C/N value of 50 dB or more and the erasure rate of 27 dB or more are maintained even after repeated recording and erasing 10' times or more. That is, it was demonstrated that by using a hydrogen-containing SiN protective film formed by ECR plasma CVD, excellent repeatability and high recording sensitivity can be ensured at the same time. The reason why the protective film formed using the ECR plasma CVD method exhibits high repetition characteristics is that it has strong adhesion and low stress, so it is difficult to deform even during repeated heat cycles for recording and erasing, and has a large protective effect on the recording film. It's for a reason. In fact, the high hydrogen-containing Si used in this example
The stress of the N film was low at about 1.09 x 10'dyn/2 mouths, and the adhesion was good at about 80 kg/am2.

Example 2 SiN film hydrogen content 2.08×22H as protective film material
Repeated evaluations similar to those in Example 1 were performed using atoms/am2. The medium configuration is the same as in the first embodiment.

The measurement was performed at a linear velocity of 10 m/s and a recording condition of 5 MHz (50 ns
)-14mw/7mw override mode was performed. The results are shown in FIG.

From this, it can be seen that the initial characteristics are maintained even after repeated recording and erasure 106 times or more.

That is, since the hydrogen content is small as shown in Example 1, the recording sensitivity is slightly lowered, but recording is possible at 15 mw and the repeatability is also good. Table 1 other than this
We investigated the recording/erasing repetition characteristics of the protective films formed under each of the conditions shown in 2. All of them maintained a C/N value of 50 dB or more and an erasure rate of 27 dB or more after 106 repetitions. It showed good repeated durability. This is a thin film with low residual stress and high adhesion formed by ECR plasma CVD method (stress: tensile 8×” to compressive 1°5
XIO” (Iy mouth/cI [12, adhesive force; 80 kg/
This study demonstrates that excellent repeatability can be ensured by using an an2 or higher).

Regarding the protective film composition, Slo, S from 5No4
The film composition rich in i lost its transparency and became absorbent at a wavelength of 830 nm, making it unsuitable as a protective film for optical disks. Also Slo, 4NO,
Films with a film composition richer in N than @ had a brittle film quality and could not be used as a protective film.

When the hydrogen content is less than 1.times.10"atoms/cm.sup.2", the recording sensitivity is 17 to 18 mn, and there is little improvement in the recording sensitivity of the SiN protective film formed by conventional sputtering. Furthermore, the hydrogen content is 4 x 1010
When the value exceeds 22ato/Cm', the thermal stability of the protective film and the adhesion of the film deteriorate, and the repeatability of recording and erasing tends to decrease to 104 to 105 times.

Regarding membrane stress, compressive stress 3 x 109dyn/
an 2 or more, and tensile stress I x 10dyn
When a protective film with a thickness of /cm 2 or more is used, peeling of the protective film and local stress release tend to occur, and the recording/erasing repeatability is as low as about 10 4 to 10 5 times.

Regarding the adhesion force to the substrate, the adhesion force is SiXN0k.
Recording of optical discs using a protective film of g/a112 or less
The number of erasing repetitions was as low as 104 to 105 times.

Furthermore, when a sputtered SiN protective film is used, since it does not contain hydrogen, the recording sensitivity is poor at 18 mW, and the stress and adhesion are also inferior to the ECR-3iN film, and the repeatability is only about 10' times. It stopped.

Above, specific results have been shown regarding simultaneously securing high repetition durability and high recording sensitivity using a protective film formed by ECR plasma CVD method. The reason for the improvement in repeated durability is that because a thin film with low residual stress was used, there is almost no release of thermal stress due to repeated recording and erasing, and irreversible deformation is suppressed. It is conceivable that the improvement in adhesion and tightness contributes to improvement in the mechanical strength of the protective film itself and in the adhesion at the interface between the protective layer and the recording film.

It is also believed that the improvement in recording sensitivity is due to the fact that the hydrogen in the thin film lowers the thermal conductivity, and the input laser power efficiently contributes to increasing the temperature of the recording film.

More specifically, the main point of the present invention is to demonstrate that the above two characteristics are not contradictory, but are compatible.

In this example, an example was shown in which it was applied as a protective film for a phase change optical recording medium, but it could also be formed by the ECR plasma CVD method as a protective film for a magneto-optical medium or a photon mode optical recording medium using a photochromic compound. It is clear that the protective film has the effect of improving repeated durability and weather resistance due to its good adhesion and tightness, and simultaneously improves the recording sensitivity due to the effect of containing hydrogen.

(Effects of the Invention) As described above, the protective film for an optical recording medium of the present invention has a hydrogen-containing SiN protective layer provided on both sides of a thin film recording layer.
By using the plasma CVD method, ■ By using a protective film with low residual film stress, high adhesion, and high density, it is possible to prevent deterioration of disk performance due to repeated recording and erasing. ■ Contains hydrogen. Effects such as high sensitivity can be achieved by thermal conductivity control by this method, and the effect of contributing to higher performance of phase change optical disk media is very large.

In addition, the recording sensitivity can be adjusted by changing the thermal conductivity of the protective film and the hydrogen content, so it is not only possible to put into practical use high-speed media with linear speeds of 30 m/s or more, but also provide protection that can accommodate specifications in the medium and low linear speed ranges. Another advantage is that the membrane can be realized without changing the material system.

[Brief explanation of drawings]

Figure 1 shows SiN fabricated by ECR plasma CVD method.
Repeatability characteristics showing the relationship between the hydrogen content of the protective film and the recording sensitivity (hydrogen content 3.20 x 10"Hatoms/C
m ”; recording sensitivity 11 mw), override repetition characteristics when using the third ZUN protective film (hydrogen content 2.08x 1022Hatoms/CI[l
2; recording sensitivity 14 mw).

Claims (1)

[Claims] 1. Electron cyclotron resonance (ECR) plasma CVD
In a protective film for an optical recording medium in which a protective film is formed on both sides of a thin film recording layer of an optical recording medium using a method, the material of the protective film is Si_XN_1_-_X: (0.4≦X≦0.6).
and hydrogen from 1×10^2^2 to 4×10^2
A protective film for an optical recording medium, characterized in that it contains ^2atoms/cm^3. 2. In the protective film for an optical recording medium according to claim 1, the residual film stress of the protective film is compressive 3×10^9.
dyn/cm^2 ~ Stress 0 ~ Tensile 1 x 10^9dy
A protective film for an optical recording medium, characterized in that the adhesive force of the protective layer to the polycarbonate substrate is 50 kg/cm^2 or more.