JPH03104038A - Formation of protective layer for optical disk - Google Patents

Abstract

PURPOSE:To obtain the protective layer which does not peel and crack in high- temp. and high-humidity environment by forming the protective layer to be provided between a substrate and a recording layer under a specific sputtering pressure by using silicon oxynitride having a specific compsn. CONSTITUTION:The protective layer 2 consisting of the silicon oxynitride having the refractive index at 830nm wavelength ranging 1.8 to 2.1 is provided between the plastic substrate 1 and the recording layer 3. The sputtering gaseous pressure P (mTorr) when the refractive index at 83-nm wavelength after oxygen is removed from the silicon oxynitride is destinated n0 is adjusted to the ranges of equation I and equation II at the time of forming the layer 2 by a sputtering method. The crack resistance degrades if the gaseous pressure P is higher than the range of the equation II and the peeling resistance degrades if the pressure is lower than this range. The barrier property to oxygen and water degrades if the pressure is higher than the range of the equation I and the formation of the stable sputtered film is difficult if the pressure is lower than this range. The protective layer having the excellent environmental resistance is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in a method for forming a protective layer for an optical disk by sputtering. In more detail,
The present invention relates to the form and method of a protective layer for optical discs to provide highly reliable optical discs that have excellent environmental resistance and do not peel or crack even under harsh environments of high temperature and high humidity. It is related.

BACKGROUND OF THE INVENTION In recent years, optical disks have attracted attention as a recording medium that plays a central role in an advanced information society, and research is actively underway. These optical discs include read-only types such as compact discs, write-once types that allow information to be recorded and played back, and rewritable types that allow information to be recorded, erased, and played back, and each uses a unique recording material. There is.

By the way, the recording materials used in various optical discs, especially the recording materials used in the above write-once and rewritable optical discs, are generally chemically unstable and are therefore often used together with a protective layer.

The function of this protective layer is mainly to block out moisture and oxygen in the environment to prevent deterioration of the recording layer, so the protective layer's constituent materials include dielectrics with excellent barrier properties against water and oxygen,
For example, magnesium, aluminum, silicon, titanium,
Oxides, nitrides, fluorides, sulfides of zinc, germanium, zirconium, tantalum, rare earth elements, etc., or composites thereof are often used.

The present inventors previously proposed a film structure as a silicon oxynitride composition desirable as a protective layer (Japanese Patent Application No. 1-14549).
No. 3). Sputtering is generally advantageous for forming a protective layer having such a structure and film structure.

Since the sputtering method is also excellent in terms of productivity, it has recently become popular as a method for manufacturing optical discs. However, in this sputtering method, it is known that the structure of the formed thin film greatly depends on certain film conditions and is controlled by factors such as gas pressure and input power. The optimal conditions for forming a protective layer depend on the general structure of the protective layer, so it is not possible to form a fully satisfactory protective layer by independently controlling factors such as the gas pressure and input power. The problem is that it is difficult to obtain.

In other words, if the conditions are incorrectly set, the protective layer that is formed will not be able to fully demonstrate its performance, leading to the undesirable situation of not being able to obtain a highly reliable optical disc. This has been an obstacle to the stable supply of

Problems to be Solved by the Invention The present invention solves the problems associated with forming a protective layer for an optical disk using the conventional sputtering method, and has excellent environmental resistance and can be peeled off even in harsh environments of high temperature and high humidity. The purpose of this work is to provide a method for providing highly reliable optical discs that are free from cracks and cracks.

Means to Solve the Problem In general, silicon nitride has excellent mechanical strength and is resistant to cracking even in harsh environments of high temperature and humidity, but its adhesion to plastic substrates is poor. Bad,
Silicon oxides have the disadvantage of being easily peeled off, whereas silicon oxides have excellent adhesion to plastic substrates and are less likely to peel off, but are inferior to nitrides in terms of mechanical strength.
The disadvantage is that cracks are likely to occur.

On the other hand, when a protective layer is deposited by sputtering, a low gas pressure generally forms a dense thin film and provides a protective layer that is less prone to cracking. It becomes easy to peel off from the surface, and conversely, the gas pressure is high,
Although this reduces the residual stress and makes peeling from the substrate less likely, the film structure becomes rougher and cracks are more likely to occur.

As a result of intensive research into the shape of the protective layer for optical discs by sputtering, the present inventors found that when silicon oxynitride is used as the protective layer, in the case of a composition with a high oxygen content, it is possible to use a low gas pressure and a high nitrogen content. By selecting sputtering conditions according to the composition of the protective layer, such as sputtering at high gas pressure in the case of assembly, it is possible to form a protective layer that combines the advantages of both silicon oxide and nitride. Based on this finding, the present invention has been completed.

That is, in the present invention, the refractive index at a wavelength of 830 nm provided between the plastic substrate and the recording layer is 1.8 to 1.
When forming a protective layer for an optical disk from the silicon oxynitride of 2.1 by sputtering, the sputtering pressure P (m
Torr), l. O≦P≦5.0...(
I) and 10.0-2.5no≦P≦12.0-2.5n-
= (i[ ) (where n0 is the refractive index at a wavelength of 830 nm of silicon nitride obtained by removing oxygen from the silicon oxynitride). It is something.

The present invention will be explained in detail below.

In the method of the present invention, silicon oxynitride having a refractive index in the range of 1.8 to 2.1 at a wavelength of 830 nm is used as the protective layer provided between the plastic substrate and the recording layer. The group of silicon oxynitride can of course be expressed by the Atsuko ratio, but since the refractive index in the infrared region has a monotonous relationship with the group, optical characteristics can be understood by expressing the group by the refractive index. This is advantageous both in terms of ease of measurement and in terms of ease of measurement.

When the refractive index of the silicon oxynitride is kept constant, the refractive index at a wavelength of 830 nm when oxygen is removed is n0
Then, the smaller no is, the larger the proportion of nitrogen is, and n0
The larger the value, the greater the proportion of oxygen. In the present invention, the sputter gas pressure P (mTorr) is 10.0-2.5n-≦P≦1.2.0-2.5n-
= (II). If the value of P is higher than the range of formula (If), the crack resistance will decrease, and if the value of P is lower than the range of formula (II), the peeling resistance will decrease.

Furthermore, the value of P is 1.0≦P≦5.0...(
It is necessary to be within the range of 1). This P is 1.0m
If the value is less than 5.0, the discharge will be irregular and it will be difficult to form a stable sputtered film. Barrier properties deteriorate, making it difficult to prevent corrosion of the recording layer. Furthermore, the refractive index of silicon is approximately 3.
．． 8. Silicon nitride Si3N. Since the refractive index of is about 1.8, the value of n0 lies between about 1.8 and 3.8.

The film thickness of a certain protective layer made of silicon oxynitride is usually lO~
It is selected within a range of 200 nm. In the optical disc obtained by applying the method of the present invention, a protective layer may be provided on the recording layer, if desired, in order to prevent oxidation and corrosion of the recording layer. As the material constituting this protective layer, dielectric materials such as silicon oxide, silicon nitride, aluminum nitride, zinc sulfide, or composites thereof are preferably used. Furthermore, an interference layer or a reflective layer may be provided for the purpose of improving the reflectance and contrast of the optical disc.

FIG. 1 is a sectional view showing the structure of an example of an optical disk obtained by applying the method of the present invention, in which a plastic substrate l
On top of the silicon oxynitride protective layer 2 formed by the method of the present invention.
, a recording layer 3, a protective layer 4, and a reflective layer 5 are sequentially provided. There are no particular restrictions on the recording layer in the above configuration; for example, in the case of a write-once type, it may be of an aperture type or a phase change type, or it may be one using an organic dye, or it may be of a rewritable type. In this case, it may be a magneto-optical type or a phase change type. Further, as the material of the plastic substrate, for example, acrylic resin, epoxy resin, polycarbonate resin, polyolefin resin, etc. can be used.

The method of the present invention can be applied to any of read-only type, write-once type, and rewritable type optical disks, and can also be applied to optical recording media other than optical disks having a similar configuration, such as optical cards, by the sputtering method. It can also be applied in cases.

Effects of the Invention According to the present invention, between the plastic substrate and the recording layer,
It is possible to provide a protective layer that does not cause peeling or cracking even under harsh environments of high temperature and high humidity, thereby providing a highly reliable optical disc with excellent environmental resistance.

Examples Next, the present invention will be explained in more detail with reference to examples.
The present invention is not limited in any way by these examples.

Example 1 A protective layer 2 made of silicon oxynitride with a thickness of 10'nm and a TbzoFe7oCOt with a thickness of 20nm were deposited on a polycarbonate substrate l as shown in FIG. 1 by sputtering.
A magneto-optical disk was fabricated by sequentially providing a recording layer 3 starting from a recording layer 3, a protection layer 4 made of silicon nitride with a thickness of 35 nm, and a reflective layer 5 made of aluminum with a thickness of 60 nm.

The protective layer 2 is formed by RF magnetron sputtering by introducing a mixed gas of argon, oxygen, and nitrogen into a silicon target. This controlled the sputtering gas pressure. Note that when the gas pressure was less than 1.9 mTorr, the discharge became unstable, and when the gas pressure was 0.8 mTorr, sputtering was practically impossible.

In order to determine the composition, a thin monolayer obtained by removing only oxygen from the formation conditions of the protective layer 2 was formed on a microscope slide glass separately from the disk, and its refractive index n0 was measured. The useful power was 3.0kW in both cases. The recording layer 3 was formed by DC magnetron sputtering using an alloy target of the constituent elements at a gas pressure of 0.4 Pa and a power of 0.5 kW.

The protective layer 4 is formed by RF magnetron sputtering by introducing a mixed gas of argon and nitrogen into a silicon target, and the nitrogen partial pressure is 0.06 Pa. The total pressure was 0.6 Pa. The reflective layer 5 is formed by DC magnetron sputtering using an aluminum target at a gas pressure of 0.2 Pa and a power of 1 kW.
Form it with Iko.

Two magneto-optical disks thus obtained were bonded together using a hot-melt adhesive and left in an accelerated life test environment of 80° C. and 90% RH. FIG. 2 is a graph showing the relationship between n0 and the pit error rate (BER) of the outer periphery of the disk at each sputtering pressure and the shape of the protective layer 2 for the magneto-optical disk after a 1000-hour test. In this figure, A is a sputter pressure of 1.5 mTorr, B is a sputter pressure of 2.
QmTQrr, C is 3.0mTorr, D is 4. OmT
orr, E is 5. OmTorr. F is 6.0mTo
It is rr.

From Figure 2, the reliability of the magneto-optical disk evaluated by BER depends on the composition of the protective layer 2 and the gas pressure, and the more reliable the gas pressure region is, the higher the no, that is, the more oxygen there is. It can be seen that the gas pressure is becoming low.

Next, defects occurring in the magneto-optical disk subjected to the above test were identified using an optical microscope, and conditions for forming the protective layer 2 were investigated, and the results shown in FIG. 3 were obtained. In the figure, the ◯ marks indicate the conditions for forming the protective layer 2 (no, sputtering gas pressure) when no defects occur, and the x marks indicate the conditions for forming the protective layer 2 when defects occur.

From FIG. 3, the sputtering gas pressure of the protective layer 2 is set to P(+nTo
rr), peeling occurs in the protective layer 2 around the outer periphery of the disk in the region where 10.0 − 2-Ono> P, and when P > 12.0 − 2.5n. Cracks occurred in the area where P was 5.5, and no peeling or cracking occurred in the opposite area.
If P exceeds 0, corrosion of the recording layer of several micrometers will occur over the entire surface of the disk, causing errors, and if P exceeds 1.
．． It has been found that when the value is less than 0, the discharge becomes irregular and stable sputtering or films cannot be formed.

From the above results, the sputtering gas pressure P (mTo
rr) is 10.0-2.5n. ≦P≦12-0 − 2.5
n. In a region that satisfies the relational expression, it is possible to manufacture a magneto-optical disk without peeling or cracking, and to prevent corrosion of the recording layer, P≦5.0. Also, to perform sputtering or film stably, It has become clear that it is sufficient to satisfy 1.0≦P.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the grooves of an example of a magneto-optical disk obtained by applying the method of the present invention, and FIGS. 2 and 3 are magneto-optical disks obtained by applying the method of the present invention FIG. 3 is a diagram showing reliability of a disk. In FIG. 1, the reference numeral 1 is a substrate, 2 and 4 are protective layers, 3 is a recording layer, and 5 is a reflective layer. Figure 1 Figure 2 1.8 2.0 2.2 2.4 2.6
2.8 3.0 3.2 E4! L6 3.8 (N-rich) Figure 3 no (0-rich)

Claims (1)

[Claims] 1. In forming a protective layer for an optical disc made of silicon oxynitride having a refractive index of 1.8 to 2.1 at a wavelength of 830 nm and provided between a plastic substrate and a recording layer by sputtering, Sputtering pressure P (mTorr) is 1.0≦P≦5.0 and 10.0-2.5n_0≦P≦12.0-2.5n_0
(However, n_0 is the refractive index at a wavelength of 830 nm of silicon nitride obtained by removing oxygen from the silicon oxynitride.) A method for forming a protective layer for an optical disc.