JPH01169748A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical information recording medium which is prevented of oxidation corrosion and has good recording and reproducing characteristics by adopting GeTe added with Cu for the essential component of a thin optical recording film and specifying the content of the Cu to the ratio lower than the average content on a substrate side. CONSTITUTION:The thin optical recording film 12 is formed by a sputtering method and vapor deposition method. Namely, a polycarbonate substrate 11 is mounted to the rear face of a rotary type substrate supporting table 22 provided in the upper part in a vacuum vessel 21 and after the inside of the vessel 21 is evacuated, an inert gas such as Ar is introduced therein and high-frequency electric power is impressed simultaneously to a GeTe target 23 and a Cu target 24. The Cu is incorporated into the thin film at the ratio below the average of the substrate side and above the average on a protective film side if the electric power to be impressed to the Cu target is regulated small in the initial period of starting the sputtering and large near the end thereof. The oxidation corrosion starting from the protective film side is prevented and the deterioration in the recording and reproducing characteristics by the addition of the Cu is decreased on the substrate side. The recording medium which is capable of making recording and reproducing exactly over a long period of time is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which information is recorded and reproduced using a light beam.

[Conventional technology]

Germanium telluride (GeTe) is a suitable material as an optical recording material because it has high recording sensitivity and can increase the signal-to-noise ratio of a reproduced signal.

Now, optical information recording media are sometimes used for the purpose of long-term storage of data, and it is necessary that the recording material does not change even if left in high-temperature environments and that recorded data can be read and written accurately. .

Regarding this point, the thin film of GeTe material gradually oxidizes and corrodes in a high temperature and high humidity environment.
There is a phenomenon in which optical properties such as reflectance and i3 pass rate change.

This can be attributed to the fact that although the GeTe crystal has a rhombohedral structure, there are gaps through which other atoms with small atomic radii can enter. In other words, the distance between Ge-Te bond atoms in an amorphous GeTe thin film is not uniform (it has a very wide distribution, so when a GeTe thin film is exposed to a high temperature and high humidity environment, the atomic radius changes). A small amount of oxygen enters this gap, forming Ge-Te and Ge-Ge.

Cut the Te-Te bond, G e Oz, , T e
01 and gradually oxidizes the thin film.

For this reason, in the past, GeTe thin 1112 was coated with an inorganic thin film such as oxide or nitride to provide protection.
However, the deterioration of the GeTe thin film in a high-humidity environment was prevented, but it took a long time to prepare the above-mentioned protective film, and there were problems in the optical information recording medium manufacturing process. This method has the drawbacks of complication and an increase in media manufacturing costs.

The present applicant has solved these drawbacks by adding Cu to GeTe material as a recording thin film that can provide an optical information recording medium that can accurately record and reproduce information even when left in a high-temperature environment.
We have discovered a recording thin film made of a material doped with . Like this, Cu
In the GeTe thin film doped with C11, the gaps in the Ge-Te lattice are filled in advance by Cu atoms, making it difficult for oxygen to penetrate (in addition, the slight amount of oxygen that penetrates combines with C11 to form CuO). Since it is stable, Ge
The Te thin film is protected from deterioration due to oxygen intrusion.

[Problems to be Solved by the Invention] However, although the optical information recording medium using the Cu-doped GeTe thin film as an optical recording film has a longer lifespan, as the Cu content increases, the signal-to-noise ratio (CNR) gradually decreases. deteriorates and Cu
If the amount of Cu content is 3 atomic percent or more, it is difficult to obtain reliable performance as an optical information recording medium, and if the amount of Cu is reduced, the service life will not be extended much.

That is, when the GeTe thin film is irradiated with a recording light beam and transitions from an amorphous phase to a crystalline phase, the distribution of distances between GeTe bond atoms becomes uniform, and Cu atoms change to the crystalline phase Ge-Te.
The amount that can enter the lattice is limited, and Cu atoms that were in the amorphous phase Ge-Te lattice are expelled from the Ge-Te crystal lattice by crystallization of the GeTe thin film, and Cu is precipitated. Therefore, it is thought that this precipitated Cu changes the reflectance of the reproduction light beam and becomes a noise component, lowering the CNR.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a method for solving the problems described above.
is a thin film mainly composed of GeTe to which Cu is added, and the Cu content in the optical recording thin film is smaller than the average Cu content on the substrate side, and the average Cu content on the protective film side is smaller than the average Cu content on the substrate side.
The content was made larger than the quantity.

[Effect]

In an optical information recording medium consisting of an optical recording thin film formed on a substrate and a protective film formed on the optical recording U thin film, the thickness of the protective film is 1/100 to 1/1 of the thickness of the substrate. /
10, the oxidative corrosion of the optical recording thin film in a high temperature, high humidity environment starts from the protective film side and gradually spreads to the substrate side. Therefore, as in the present invention, Cu in the optical recording thin film
Protection 1 by making the content smaller than the average Cu content on the substrate side
By making the Cu content larger than the average Cu-containing vinegar on the 1 side, oxidative corrosion of the optical recording thin film that progresses from the protective film side can be strongly prevented. Furthermore, since information is generally recorded and reproduced by making a light beam incident from the substrate side, the recording and reproduction characteristics of an optical information recording medium depend more strongly on the properties of the optical recording thin film on the substrate side. Therefore, if the Cu content on the substrate side of the optical recording film H9 is smaller than the average Cu content as in the present invention, there will be less precipitated Cu, which becomes a noise component, on the substrate side, and as a result, the recording and reproducing characteristics will deteriorate. Can be kept in good condition.

[Embodiment] FIG. 1 shows an embodiment of an optical information recording medium according to the present invention. That is, reference numeral 11 is a polycarbonate substrate, on which a Cu-doped Ge film is formed as an optical recording thin film.
A Te thin film 12 is present.

Furthermore, a resin protective film 13 was laminated on the optical recording thin film to prevent scratches and dust.

Here, the substrate 11 is not limited to polycarbonate, but may be conventionally known PMMA or polyolefin.

A transparent resin plate such as epoxy or a glass plate can be used.

The optical recording thin film 12 is produced by a sputtering method and a vapor deposition method. A method of making the Cu content smaller than the average Cu content on the substrate side and larger than the average Cu content on the protective film side in a Cu-doped GeTe thin film will be described below.

FIG. 2 is a schematic diagram of a sputtering apparatus used when producing the optical recording film (1). The polycarbonate substrate 11 is attached to the lower surface of the rotary substrate support table 22 provided at the upper part of the vacuum chamber 21, and the inside of the vacuum chamber 21 is
After evacuation to X10-'Pa, an active gas such as Ar is introduced into the vacuum chamber 21 to make the gas pressure 5XIO"Pa. In this state, when high-frequency power is simultaneously applied to the GeTe target 23 and the Cu target 24, A GeTe thin film doped with Cu is formed on the substrate 11 by the spackle action.At this time, as shown in FIG. When the power is decreased at the beginning of the sputtering and increased near the end, in the Cu-doped GeTe thin film, the Cu content is lower than the average Cu content on the substrate side, and the average Cu content is lower than the average Cu content on the protective layer side.
It becomes larger than the u content.

Similarly, in the vacuum evaporation method, when GeTe and C11 are simultaneously evaporated from two evaporation sources, the evaporation rate of GeTe is kept constant, and the evaporation rate of Cu is small at the beginning of evaporation and increases near the end. On the CU-containing substrate side, the Cu content is smaller than the average Cu content, and on the protective film side, the Cu content is larger than the average Cu content.

The resin protective film 13 is formed by applying an ultraviolet curable resin liquid using a spinner, and then irradiating ultraviolet rays to cure the resin and form a film. For the resin protective film 13, not only an ultraviolet curable resin but also a moisture curable resin, a two-component reactive resin, and a solvent-based resin can be used.

Comparative optical information recording media were prepared by keeping the power applied to the Cu target constant during the production of the Cu-doped GeTe optical recording thin film, and by changing the power applied to the Cu target during sputtering as shown in Figure 3. Table 1 shows a comparison of the life span of the optical information recording medium and the signal-to-noise ratio CNR of the reproduced signal of the optical information recording medium according to an embodiment of the present invention.

Table 1 Here, the medium life is determined when a disk-shaped optical information recording medium is irradiated with a laser beam and the number of rotations is 180 or ρm.

Record the signal of frequency IMH2, J lSc5024M
-1 temperature and humidity accelerated test was conducted, and the focus error rate was estimated from the test time until it became three times the value before the test.

As shown in Table 1, according to the above example, the optical information recording medium has a Cu content smaller than the average Cu content on the substrate side and smaller than the average Cu content on the protective film side in the optical recording thin film. Since the size is large, the medium life is long and the reproduced signal CNR maintains a good value.

(Effects) According to the present invention, since the Cu content in the optical recording thin film is larger than the average Cu content on the protective film side, oxidative corrosion of the optical recording thin film starting from the protective film side is prevented. An optical information recording medium that can accurately record and reproduce information for a long time even when left in a high temperature and high humidity environment can be obtained. Furthermore, since the Cu content on the substrate side of the optical recording thin film is smaller than the average Cu content, the deterioration of recording and reproducing characteristics due to Cu addition is small, and an optical information recording medium with good recording and reproducing characteristics can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of an optical information recording medium according to the present invention, FIG. 2 is a schematic diagram of a sputtering apparatus applicable to the present invention, and FIG. 3 is a diagram for explaining its operation. 11... Substrate 12... Optical recording thin film 13... Resin protective film 21... Vacuum chamber 22... 7S plate support table 23... GeTe target 24... Cu target agent Patent attorney Yama Kazumi Kuchi,,7. ．． 7
・) No. t Figure 2 Figure 2 Procedures (City Correction F (Spontaneous May 1988) 0th 1.1V (Ushi no 1988 Gincho Shin n No. 326885 2, Name of Invention Controversially 4-fold 3. Relationship with Hanyu, the person making the amendment Patent Applicant Address 4-14-14 Akasaka, Minato-ku, Tokyo 107 Name (416) Nippon Columbia Co., Ltd. Class Q Emperor
July Kazuo 4, Ioyu Town l, ^, Address 5-1 Minato-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture 210 Showa Year Month Day (all dates) 6, subject to amendment fi+ Specification, page 6 Lines 16 to 18, "The inside of the vacuum chamber 21 will be..." is changed to "After the inside of the vacuum chamber 21 is evacuated to approximately 5X10-'Pa, 4 active gases such as Ar are added to the vacuum chamber 21. to make the gas pressure 5×10-'Pa.''

Claims (1)

[Claims] In an optical information recording medium comprising an optical recording thin film formed on a substrate and a protective film formed on the optical recording thin film, the main component of the optical recording thin film is Cu-doped GeTe,
An optical information recording medium characterized in that the Cu content in the optical recording thin film is smaller than the average Cu content on the substrate side.