JP2596901B2 - Optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium on which information is recorded and reproduced using a light beam.

[Conventional technology]

GeTe, GeSnTe, GePbTe, GeSnPbTe (these materials are referred to as G
eTe-based material) is a preferable material as an optical recording material, which has high recording sensitivity and can increase the signal-to-noise ratio of a reproduced signal.

Optical information recording media are sometimes used for long-term storage of data, and it is necessary that there is no change in the recording material even when left in a high-temperature, high-humidity environment, and that the recorded data can be read and written accurately. is there.

In this regard, GeTe-based materials have their thin films gradually oxidatively corrode in high-temperature and high-humidity environments,
There is a phenomenon that the optical properties of reflectance and transmittance change.

The cause of this is that the GeTe crystal has a rhombohedral structure, but there is a gap into which other atoms having a small atomic radius can penetrate. That is, since the Ge-Te bond atomic distance in the amorphous phase GeTe thin film is not uniform and has a very wide distribution, when the GeTe thin film is placed in a high-temperature and high-humidity environment, oxygen having a small atomic radius is reduced. Penetrates this gap, breaks the Ge-Te, Ge-Ge, Te-Te bond,
O ₂ and TeO _{2 are formed} and the thin film is gradually oxidized.

For this reason, conventionally, an inorganic thin film such as an oxide or a nitride is applied to a GeTe thin film to form a protective film, which is used in a high-temperature, high-humidity environment.
Although the deterioration of the GeTe thin film was prevented, it was determined that it took a long time to prepare the protective film, complicated the optical information recording medium manufacturing process, and increased the medium manufacturing price.

The present applicant has solved such disadvantages, and added nitrogen to GeTe-based material as a recording thin film capable of providing an optical information recording medium capable of accurately recording and reproducing information even when left in a high temperature and high humidity environment. A recording thin film of the material was found. In such a GeTe-based thin film to which nitrogen is added, oxygen is difficult to penetrate because the gaps in the Ge-Te lattice are buried in advance by nitrogen atoms. Is done.

[Problems to be solved by the invention]

However, although the optical information recording medium using the above-mentioned nitrogen-added GeTe-based thin film as an optical recording film has a long life, as the nitrogen content increases, the signal-to-noise ratio (CNR) gradually deteriorates, and
If the content is more than 2 atomic percent, there is a problem that it is difficult to obtain a reliable performance as an optical information recording medium, and if the nitrogen content is reduced, the life is not extended much.

That is, when the GeTe-based thin film is irradiated with the recording light beam and changes from an amorphous phase to a crystalline phase, the distribution of the distance between GeTe bonding atoms is made uniform, and nitrogen atoms enter the crystalline phase Ge-Te lattice. The amount that can enter is limited, and nitrogen atoms in the amorphous phase Ge-Te lattice are rejected out of the Ge-Te crystal lattice by crystallization of the GeTe thin film, and nitrogen atoms precipitate. Therefore, it is considered that the deposited nitrogen atoms change the reflectivity of the reproduction light beam, become a noise component, and lower the CNR.

[Means for solving the problem]

The present invention, in order to solve the above problems, the recording thin film is a thin film mainly composed of nitrogen-added GeTe, the nitrogen content in the optical recording thin film on the substrate side than the average nitrogen content It was also made smaller than the average nitrogen content on the protective film side.

[Action]

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,
Since the thickness of the protective film is about 1/100 to 1/10 of the thickness of the substrate, the oxidative corrosion of the optical recording thin film in a high-temperature and high-humidity environment starts from the protective film side and gradually spreads to the substrate side. Therefore, as in the present invention, the nitrogen content in the optical recording thin film is made smaller than the average nitrogen content on the substrate side and larger than the average nitrogen content on the protective film side, so that the optical recording thin film progresses from the protective film side. Oxidative corrosion can be strongly prevented. In general, information recording and reproduction are performed by irradiating a light beam from the substrate side, so that the recording and reproduction characteristics of the optical information recording medium strongly depend on the properties of the optical recording thin film on the substrate side. Therefore, when the nitrogen content on the substrate side of the optical recording thin film is smaller than the average wane content as in the present invention, the amount of deposited nitrogen which is a noise component on the substrate side is small, and as a result, the recording / reproducing characteristics are also reduced. Can be kept good.

〔Example〕

FIG. 1 shows an embodiment of the optical information recording medium according to the present invention. That is, reference numeral 1 denotes a polycarbonate substrate on which GeTe added with nitrogen as an optical recording thin film is provided.
It has a thin film 12. Further, a resin protective film 13 for preventing scratches and dust was laminated on the recording thin film.

Here, the substrate 11 is not limited to polycarbonate, but may be a conventionally known transparent resin plate such as RMMA, polyolefin, epoxy or the like, or a glass plate.

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

FIG. 2 is a schematic diagram of a sputter rig used for producing the optical recording thin film. The polycarbonate substrate 11 is mounted on the lower surface of the rotary substrate support table 22 provided at the upper part in the vacuum chamber 21. After evacuation of the vacuum chamber 21 to about 5 × 10 ⁻⁴ Pa, A gas mixture with an active gas is introduced to adjust the gas pressure to 5 × 10 ^-1 Pa.

When sputtering is performed using a GeTe target 23 in this mixed gas, the nitrogen-added GeTe
A thin film is formed. At this time, when the nitrogen gas distribution in the mixed gas is reduced at the beginning of the sputtering start and increased near the end of the sputtering, in the GeTe thin film to which nitrogen is added, the nitrogen content is smaller than the average nitrogen content on the substrate side, and the protective film is formed. Side will be greater than the average nitrogen content.

In the vacuum deposition method, a nozzle that can introduce gas from outside the vacuum chamber is placed near the ionization electrode provided on the GeTe evaporation source, and GeTe is evaporated while blowing nitrogen gas around the ionization electrode in the vacuum chamber. Then, GeTe is ionized and reacts with nitrogen to obtain a GeTe thin film containing nitrogen. At this time, if the flow rate of the nitrogen gas introduced into the vacuum chamber is kept small at the beginning of the deposition and increased near the end while the evaporation rate of GeTe is kept constant, the nitrogen content on the substrate side is smaller than the average nitrogen content, and the nitrogen content on the protective film side is small. Can be greater than the average nitrogen content.

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

An optical information recording medium for comparison produced at a constant nitrogen partial pressure in the mixed gas during the production of the nitrogen-added GeTe optical recording thin film,
In the optical information recording medium according to the embodiment of the present invention, in which the nitrogen partial pressure in the mixed gas is gradually increased during sputtering, the life of the optical information recording medium and the signal-to-noise ratio CNR of the reproduced signal are set to the first values.
Shown in comparison with the table.

Here, the medium life was measured by irradiating a disk-shaped optical information recording medium with laser light, recording a signal at a rotation speed of 1800 rpm and a frequency of 1 MHz, performing a temperature / humidity acceleration test of JISc5024M-1, and measuring the bit error rate before the test. It was inferred from the test time until it became three times the value.

As shown in Table 1, according to the above embodiment, in the optical information recording medium, the nitrogen content in the optical recording thin film was smaller than the average nitrogen content on the substrate side, and was lower than the average nitrogen content on the protective film side. Because of the increase, the medium life is long and the reproduced signal CNR keeps a good value.

〔effect〕

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

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of an optical information recording medium according to the present invention, and FIG. 2 is a schematic view of a sputtering apparatus applicable to the present invention. 11 Substrate 12 Optical recording thin film 13 Resin protective film 21 Vacuum chamber 22 Substrate support table 23 GeTe target

Claims (1)

(57) [Claims] 1. 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, wherein the optical recording thin film is mainly composed of Ge to which nitrogen is added.
An optical information recording medium comprising a Te-based material, wherein the nitrogen content in the optical recording thin film is smaller than the average nitrogen content on the substrate side.