JPH0447384B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] In order to prevent unstable oxygen in the oxide protective film of the optical record carrier substrate from deteriorating the recording medium, a rare earth metal is simultaneously deposited with an oxide and then heat treated. to completely trap unstable oxygen with rare earth metals.

[Industrial application field]

The present invention relates to a method for manufacturing a substrate for an optical record carrier,
In particular, the present invention relates to a method of manufacturing a protective film for preventing a recording medium from being adversely affected by a substrate.

[Conventional technology]

Optical disks, particularly magneto-optical disk substrates, have guide grooves on their surfaces so that laser beams for recording and reproduction can be tracked to predetermined positions on the disk. In order to make it easier to form the guide grooves, the substrate is usually a disk made of plastic or glass, on which an ultraviolet curing resin is applied and then the guide grooves are formed. However, these substrate materials contain active components such as uncured monomers, and when a rare earth-transition metal recording layer, which is a magneto-optical recording material, is directly formed on these substrate materials, the recording layer is damaged due to an oxidation reaction. Deterioration occurs. This is because the rare earth metal, which is one of the components forming the recording layer, reacts with the active components contained in these substrates. As a result, the content of rare earth metals in the alloy phase apparently decreases, leading to deterioration of magnetic properties and recording/reproducing properties.

For this reason, conventionally, a transparent protective film has been provided between the substrate and the recording layer to prevent deterioration of the recording layer. In a magneto-optical disk, a laser beam is incident from the substrate side and the reflected light is used for recording and reproduction, so the protective film must be transparent.

For this purpose, oxide materials have generally been used as protective films.

[Problem that the invention seeks to solve]

However, oxides cannot be said to be a sufficient protective film for magneto-optical disks for the following reasons. That is, when an oxide film is formed by a method such as vapor deposition or sputtering, the oxide protective film contains many structural defects, and particularly contains unstable oxygen (free oxygen). Therefore, the unstable oxygen present in the protective film reacts with the rare earth metal in the recording layer, causing the recording layer to deteriorate.

Such deterioration of recording media due to a protective film is remarkable in magneto-optical recording media using rare earth metals, but it is also common to other magneto-optical record carriers, hole-shaped optical record carriers, etc. It is desirable to provide a protective film that is inert to the medium.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides an optical recording carrier in which an oxide and a rare earth metal are simultaneously deposited on a substrate to form a protective film, and then the oxide protective film is stabilized by heat treatment. A method for manufacturing a substrate is provided.

As mentioned above, when forming an oxide film on a substrate, unstable oxygen or free oxygen is generated, but if a rare earth metal is simultaneously formed into a film with an oxide, rare earth metals have a high affinity for oxygen, so there is no possibility of non-oxidation. Oxygen is stabilized by easily combining with stable oxygen to form oxides. However, at this stage of simultaneous film formation, it cannot be said that the rare earth metal and unstable oxygen are sufficiently combined to form a stable oxide completely. Therefore, in the present invention, in order to sufficiently combine the rare earth metal and unstable oxygen to form a stable oxide, heat treatment is further performed after the film is formed. This heat treatment is performed in vacuum, air,
It may be carried out in any environment such as an inert atmosphere, but
It is preferable to carry out the process in an atmosphere containing oxygen, since this has the advantage that, for example, excess rare earth metals are also oxidized. Generally, it may be carried out in the atmosphere.

The base material to which the protective film is applied may be plastic such as acrylic resin, epoxy resin, polycarbonate resin, or glass, or may be metal if the substrate does not need to be transparent. Generally, tracking guide grooves are formed on the surface of the base material. Although the guide grooves may be formed by directly etching the plastic or glass substrate, they are usually formed by curing an ultraviolet curing resin on the surface of the substrate using a mold.

Oxides used for the protective film include _Sio2 ,
Examples include Al ₂ O ₃ , CaO, La ₂ O ₃ , MgO, Sb ₂ O ₃ and SiO.

Rare earth metals include La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,
There is Lu. The oxide and rare earth metal may be a mixture.

The protective film may be formed by a conventional simultaneous film formation method such as simultaneous vapor deposition or simultaneous sputtering of an oxide and a rare earth metal.

When the amount of rare earth metal increases relative to the oxide,
More unstable oxygen is stabilized, increasing the protective effect of the recording film. However, when the amount of rare earth metal exceeds a certain level, the protective effect becomes saturated. This is thought to be because unstable oxygen generated during oxide film formation is completely stabilized. When the amount of rare earth metal is further increased, the transparency of the protective film decreases due to the excess metal. When using the substrate side as the light input or output side, it is desirable that the absorbance of the protective film is 10% or less.
It is necessary not to use too much of the rare earth metal. In the example, the film formation rate (film thickness or volumetric growth rate) of the rare earth metal relative to the oxide was 0.4.
The protective effect was saturated at a certain level.

The thickness of the protective film is preferably several 100 nm.

Unlike ordinary oxide stabilization treatments, the heat treatment temperature can be kept quite low to be effective. However, it is preferable to carry out the treatment at a high temperature within a range that does not damage the base material, especially the plastic base material or the ultraviolet curable resin for forming the guide grooves, as this will accelerate the process. Normally, even considering the ultraviolet curing resin formed on the glass substrate, it is safe up to at least about 150°C. however,
Even if the base material can withstand high temperatures, if the temperature is too high, the adhesion between the protective film and the base material will decrease due to the difference in coefficient of thermal expansion, so the temperature is preferably 200° C. or lower, for example. Although a heat treatment time of about 1 hour is usually sufficient, a shorter heat treatment time is still effective, and a longer heat treatment time is not particularly disadvantageous other than for economic reasons.

A recording film and an upper protective film are formed on the optical record carrier substrate thus completed to complete the optical record carrier. The approach can be conventional.

〔Example〕

Example 1 An acrylic resin substrate was set in a vacuum evaporation device,
Sio ₂ , an oxide, and Tb, a rare earth metal, are used as evaporation sources, and each evaporation source is irradiated with an electron beam while rotating the substrate under a vacuum of 3 × 10 ^-5 Pa to evaporate Sio ₂ and Tb.
Tb was co-deposited onto the substrate. And Tb/Sio ₂
A protective film with a thickness of 200 nm was formed by changing the deposition rate ratio (film thickness ratio) between 0 and 0.4. 60 of these
℃, after 80 hours of heat treatment in air, rare earth -
A TbFeCo film was created as a transition metal-based medium. The preparation conditions were a vacuum level of 1.3×10 ^-5 Pa and a deposition rate of Tb:
0.23 nm/s, FeCo: 0.2 nm/s. The produced film has a coercive force Hc = 7 to 8 KOe and a Kerr rotation angle θ _K =
It was 0.35deg. Furthermore, a Si protective film with a thickness of 200 nm was formed on the TbFeCo layer without breaking the vacuum.

This disk was left in the atmosphere at 60°C and changes in coercive force were tracked. The results are shown in FIG. 1st
For comparison, the figure also shows the results for a disk in which a TbFeCo film was directly formed on the substrate without forming a protective film. Referring to Figure 1, Sio ₂ −
In the case without the Tb protective film (dashed line), the coercive force Hc increases, and this is thought to be due to oxidation by active components from the PMMA substrate. Next, with the protective film that does not contain Tb (indicated by γ = 0 in the figure), Hc changes more than in the case without the protective film, which is
This is thought to be due to oxidation of the recording film due to SiO ₂ . It is observed that the change in Hc becomes smaller as more Tb is mixed (as γ becomes larger). Furthermore, in FIG. 1, the dashed line indicates the case where no heat treatment was performed after film formation, and the solid line indicates the case where heat treatment was performed after film formation. From the changes between these, by heat treatment
It is observed that the change in Hc is becoming smaller.

Next, using these disks, heat at 60℃ and 90%
Changes in recording and playback characteristics when left at RH are shown in the second section.
As shown in the figure. From FIG. 2, it is recognized that the decrease in C/N can be reduced by applying heat treatment.

In Example 1, the heat treatment was performed at a relatively low temperature of 60° C., and as described above, it was found to be effective in stabilizing the protective film. Normally, the temperature required to heat-treat and stabilize the formed oxide film is much higher than this, but in the present invention, by simultaneously forming the oxide and rare earth metal, it is possible to simply heat-treat the oxide. This suggests that the membrane is stabilized by a different mechanism.

Example 2 Styrene resin, epoxy resin,
Example 1 also when using polycarbonate resin
obtained similar results.

Example 3 A SiO ₂ -Tb protective film was prepared in the same manner as in Example 1 using a glass disk having a resin layer with guide grooves made of an ultraviolet curable resin as the substrate material. However, in this example, the heat treatment was performed at 120°C.
It lasted 8 hours.

The obtained disk was left at 120℃ in the atmosphere to collect Hc.
We tracked changes in The results are shown in Figure 3.

Next, we tracked changes in recording and playback characteristics when the disk was left in an environment of 120°C and 90% RH. The results are shown in Figure 4.

From FIG. 3 and FIG. 4, it is recognized that by performing heat treatment, the decrease in C/N can be reduced and the life of the optical disk can be extended.

Example 4 Oxides include Al ₂ O ₃ , CaO, La ₂ O ₃ , MgO,
Similar results as shown in Examples 1 to 3 were obtained when Sb ₂ O ₃ was used and Tb was used as the rare earth element.

Example 5 SiO ₂ as oxide, La, Ce, as rare earth
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho,
Example 1 using any of Er, Tm, Yb, and Lu
- Almost the same results as in 3 were obtained.

〔Effect of the invention〕

According to the invention, an excellent substrate for an optical record carrier is provided which allows long-term stability of the optical recording material, and this substrate can be transparent. Although the above explanation was mainly related to magneto-optical record carriers, the fact that stabilization of the substrate contributes to long-term stability of the recording material also applies to write-once type, phase change type, etc. optical record carriers. This is somewhat acceptable.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the change over time in the coercive force of the optical disk of Example 1, FIG. 2 is a graph showing the change over time in the C/N ratio of the optical disk of Example 1, and FIG.
4 is a graph showing the change over time in the coercive force of the optical disk of Example 3, and FIG. 4 is a graph showing the change over time in the C/N ratio of the optical disk in Example 3.

Claims (1)

[Claims] 1. A method for producing a substrate for an optical record carrier, which comprises forming a protective film by simultaneously depositing an oxide and a rare earth metal on a base material, and then heat-treating the film to stabilize the oxide protective film.