JPH0649391B2 - Optical recording medium for DRAW - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of an optical recording medium used for recording or storing information by irradiating an energy ray such as a laser beam, and particularly to an optical disc, The present invention relates to an improvement in the composition of a perforated recording thin film used for an optical high density information recording medium such as an optical card and an optical tape.

(Background of the Invention) As a composition of a write-once (DRAW) type recording thin film used for an optical disc or the like, a metal such as Au or Ge, te-C or Te-S is used.
Te-based compositions such as e, organic substances such as cyanine, metal oxides, and the like have been proposed. The current problem with optical recording thin films is how to improve their durability without deteriorating recording / reproducing characteristics such as CNR. Although a recording thin film made of a Te-based composition has already been partially put into practical use, few of them completely satisfy both recording / reproducing characteristics and durability, and further improvement is required.

(Prior Art) Among Te-based recording thin films, tellurium (Te) and selenium (Se) are used.
The Te-Se based thin film based on Al has a good pit shape and therefore has a high CNR and good durability. In order to improve the characteristics of this recording thin film, elements other than Te and Se, such as Cd, Zn, Al, Ga, In, Sb and B, are used.
It has already been proposed to add i, Si, Sn, Pb, Ta, Cu, Ag, I and Tl (Japanese Patent Publication No. 59-35).
356). Further, there is a proposal that the durability can be improved by adding titanium (Ti) and silver (Ag) as additional elements of the third component or more.
4885. The addition of titanium and silver improves the durability of the recording film, but on the contrary, the addition of titanium deteriorates the pit shape, resulting in a problem that the CNR is lowered. Therefore, there has been a demand for the development of a recording film composition that improves durability without lowering CNR. The present invention is an extension of these studies.

(Object of the Invention) An object of the present invention is to provide a DRAW type recording film composition which does not have the above-mentioned drawbacks. That is, it is possible to satisfy both the improvement of the durability and the improvement of the recording / reproducing characteristics.
An object is to provide a Se-based perforated recording thin film composition.

(Structure of the Invention) An optical recording medium on which information is recorded by a laser beam having a recording thin film containing tellurium as a main component and further containing selenium formed on a substrate provided by the present invention is the selenium in the recording thin film. The content is 1 to 10 atom%, and the recording thin film further contains titanium (Ti) in an amount of 0.5 to 6 atom%.

The recording thin film may further contain silver (Ag) in a content of 3 atomic% or less.

The recording thin film is made of glass, plastics, ceramics,
It can be formed on a metal or any other support.
In the case of an optical disc, a transparent resin substrate such as acrylic or polycarbonate is preferable from the viewpoint of cost and productivity, and the film thickness is generally 200 to 500Å.

In the above composition, the ratio of selenium (Se) needs to be 1 to 10 atom%, preferably 3 to 8 atom% with respect to tellurium (Te). When the ratio of selenium is less than 1 atom%, the durability of the recording film is lowered, and conversely, when it exceeds 10 atom%, the recording characteristics such as recording sensitivity and reproducing characteristics are deteriorated. The content of this selenium differs depending on the type of substrate used, and in the case of an acrylic resin substrate, it is necessary to be 5 atom% or more to prevent a decrease in reflectance, that is, a decrease in durability. In this case, it may be 1 atomic% or more.

The characteristic of the present invention is that titanium (Ti) is further added to the above tellurium-selenium recording thin film composition in an amount of 0.5 to 6 atomic%. If the titanium content is less than 0.5 atom%, the durability will be poor, while if it exceeds 6 atom%, the pit shape will be poor and the reproduction characteristics, that is, CNR will be deteriorated.

The recording film composition of the present invention contains silver to increase the reflectance.
(Ag) can be added. The amount of silver added may be 3 atomic% or less, preferably 2 atomic%, and may not be added in some cases.

An optical recording medium provided according to another aspect of the present invention is an optical recording medium in which information is punched and recorded by a laser beam having a recording thin film containing tellurium as a main component and formed on a substrate. Selenium content of 1
10 atomic%, the recording thin film further contains 0.5 to 6 atomic% of titanium, and the oxygen concentration in the thickness direction of the recording thin film is near the outer surface of the recording thin film and between the recording thin film and the substrate. It is characterized in that the intermediate band between the vicinity of the outer surface and the vicinity of the interface is lower than the vicinity of the interface.

Generally, the Te—Se based recording thin film as described above is formed on a substrate by a physical vapor deposition (PVD) method such as a sputtering method or a vacuum evaporation method. In this physical vapor deposition method, the chamber is evacuated to 10
^{Although the} degree of vacuum is set to ^-3 Torr or less, oxygen is contained in the recording thin film due to the presence of oxygen originating from water, oxygen molecules, and monomers coming out from the substrate and others. In particular, when plastic is used as the substrate, it is difficult to completely remove this oxygen.

This oxygen is Te generated by the sputtering method or the vapor deposition method,
It is attached or deposited on the substrate together with Se, Ti atoms, clusters or particles. At this time, it is considered that oxygen reacts with these elements to be deposited as an oxide. These oxides improve the durability of the recording film,
On the contrary, the pit shape is disturbed and the reproduction characteristic, that is, C
Reduce NR.

As a result of continued research by the present inventors to eliminate this drawback,
By controlling the oxygen content distribution in the film thickness direction of the recording thin film as described above, it was discovered that both durability and recording / reproducing characteristics can be satisfied, and the present invention was completed.

That is, as described above, the oxygen content in the vicinity of the outer surface and the vicinity of the interface of the recording thin film is made higher than the intermediate band between the vicinity of the outer surface and the vicinity of the interface in the film thickness direction. The oxygen is Te, Se and Ti which are the constituent elements of the recording thin film.
It is considered that these oxides react with any of these to form these oxides, but as a result of analysis, this oxygen reacts with Ti to form titanium oxides. It is considered that this titanium oxide plays a role of improving the durability of the recording film. on the other hand,
In the intermediate band, titanium exists as a metal that is not an oxide, is uniformly distributed in the recording film, and has an amorphous recording film structure. It is considered that the reason why the pit shape becomes good is that the metallic titanium has a uniform distribution in this intermediate band.

The above three-layer structure of titanium oxide layer-titanium metal layer-titanium oxide layer (substrate side) is formed on the substrate by using the same target in principle and changing the oxygen concentration during sputtering of each layer. be able to. But in reality,
The above three-layer structure is formed only by sufficiently vacuum degassing and drying the substrate before the sputtering operation. The reason for this is considered as follows. That is, by sufficiently degassing and drying the substrate, oxygen, water, monomers, etc. adsorbed on the substrate are almost completely removed, and during sputtering, oxygen remaining from these components still reacts with titanium. Form a layer of titanium oxide. However, oxygen is immediately consumed or promoted to become an oxygen-free metal-like titanium above the intermediate band. On the other hand, it is considered that the vicinity of the outer surface was oxidized by oxygen in the air when the optical disk was taken out from the sputtering apparatus after sputtering.

The thickness of each layer formed by the oxide near the outer surface and near the interface varies depending on the film thickness of the entire recording film, but when the film thickness is 300Å, the thickness of each oxide film is about 1
It is 00Å or less.

Hereinafter, the present invention will be described using examples.

Example 1 An optical disk substrate (diameter 130 mm, diameter 130 mm, made of acrylic resin (PMMA) and polycarbonate resin (PC) with a pre-groove that was sufficiently deaerated by leaving it in a large vacuum deaeration dryer for 90 hours.
1.2mm thick) sputtering equipment (Tokuda Manufacturing)
And sputtering was performed under the following conditions: Argon pressure = 3 × 10 ⁻³ Torr Sputtering power = 300 W Film thickness = 300 Å Target was Te-Se alloy (composition ratio Te: Se = 75)
~ 90: 25 ~ 10) on which a chip of Ti or Ti-Ag alloy (Ti: Ag = 3 ~ 9: 1 ~ 5) was placed. Since the target composition and the film composition are different from each other, the film composition was obtained by analysis.

Using the semiconductor laser of 830 nm, write the repetitive signal of 1 MHz with the output of 6 mW on the obtained DRAW type optical disc,
The output was read at 1 mW and the CNR was measured (band = 30 kHz
z). Furthermore, the pit shape was observed by an electron microscope, and the element distribution state and valence state in the depth direction of the recording film were examined by Auger electron analysis and XPS analysis.

As can be seen from Table I, the film composition satisfying both the pit shape, that is, the recording / reproducing characteristics and the CNR change rate, and therefore the durability must be within the range defined above.

Comparative Example The same operation as in Sample No. 7 of Comparative Example 1 was repeated, but the substrate was not vacuum degassed and dried.

A micrograph of the pit shape of the obtained optical disk (Sample No. 20) and the pit shape of the optical disk of Sample No. 7 is shown in FIG.

As is clear from FIG. 2, the pit shape is greatly improved by preliminary vacuum drying of the substrate. Note that the initial stage of these membranes
CNR ₀ is 50 dB and sample number 7 in the comparative example (sample number 20)
Was 56 dB.

The results of XPS analysis and Auger electron analysis of the element distribution state and valence state in the film thickness direction of these two recording films
It is shown in the figure (Sample No. 7) and FIG. 4 (Comparative Example (Sample No. 20)). These data indicate that titanium is an oxide near the outer surface and near the interface and is in the metal state in these intermediate zones.

[Brief description of drawings]

FIG. 1 is a copy of a micrograph showing a pit shape of a recording film outside the scope of the present invention. FIG. 2 shows the first recording film of the present invention and the comparative example (sample No. 20).
The same figure as the figure. FIGS. 3 and 4 show XPS analysis and Auger electron analysis profiles of the recording film of the present invention and the comparative example (Sample No. 20).

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Claims (2)

[Claims] 1. A write-once type optical recording medium in which information is punched and recorded by a laser beam having a recording thin film containing Te as a main component formed on a substrate and further containing Se and Ti. The Se content is 1 to 10 atomic%, the Ti content is 0.5 to 6 atomic%, and the oxygen concentration in the film thickness direction of the recording thin film is near the outer surface of the recording thin film and the recording thin film and the substrate. The optical recording medium is characterized in that the intermediate region between the vicinity of the outer surface and the vicinity of the interface is lower than the vicinity of the interface. 2. Ti exists as titanium oxide near the outer surface of the recording thin film and near the interface between the recording thin film and the substrate.
The optical recording medium according to claim 1, wherein the optical recording medium exists in a substantially non-oxide state in the intermediate region in the thickness direction of the recording thin film between the vicinity of the outer surface and the vicinity of the interface.