JPH0422436B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an optical recording medium on which information is recorded and reproduced using a light beam. [Prior art] Germanium telluride GeTe has high recording sensitivity as an optical recording material, and has a low signal-to-noise ratio of reproduced signals.
It is a suitable material that can increase CNR. Now, optical information recording media are sometimes used for long-term storage of information, for example for 10 years or more, and the recording material does not change even if left in high temperature and high humidity environments, allowing recorded information to be stored accurately. Must be able to read and write. Regarding this point, GeTe material has a phenomenon in which its thin film undergoes oxidative corrosion, albeit gradually, in a high temperature and high humidity environment, causing changes in reflectance, transmittance, and optical properties. This can be attributed to the fact that although GeTe crystal has a rhombohedral structure, there are gaps through which other atoms with small atomic radii can enter. That is, Ge− in the amorphous GeTe thin film
The distance between Te crystal atoms is not uniform and has a very wide distribution, so when a GeTe thin film is placed in a high temperature and high humidity environment, oxygen with a small atomic radius enters this gap, resulting in Ge−Te, Ge -Ge and Te-Te bonds are broken, forming SeO ₂ and TeO ₂ and gradually oxidizing the thin film. For this reason, in the past, inorganic thin films such as oxides and nitrides were coated on GeTe thin films as protective films to prevent the GeTe thin films from deteriorating in high temperature and high humidity environments, but it took a long time to create the above protective films. The disadvantages are that it takes time, complicates the optical information recording medium manufacturing process, and increases the media manufacturing cost. The present applicant has developed a material in which Cu is added to GeTe material as a recording thin film that can eliminate these drawbacks and provide an optical information recording medium that can accurately record and reproduce information even when left in a high temperature and high humidity environment. discovered a recording thin film. In such a Cu-doped GeTe thin film, the gaps in the Ge-Te lattice are filled in advance by Cu atoms, making it difficult for oxygen to enter, and the small amount of oxygen that has entered combines with Cu and becomes CuO. As a result, the GeTe thin film is protected from degradation due to oxygen intrusion. [Problems to be solved by the invention] However, although the lifetime of an optical information recording medium using the Cu-doped GeTe thin film as an optical recording film becomes longer as the amount of Cu added increases, conversely, the signal-to-noise ratio CNR gradually decreases. Therefore, if the Cu content is 3 atomic percent or more, it is difficult to obtain reliable performance as an optical information recording medium, and if the Cu content 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 GeTe bond interatomic distances becomes uniform, and Cu atoms enter the crystalline phase Ge-Te lattice. The amount you can get is limited,
The Cu atoms in the lattice of the amorphous Ge−Te phase
As the GeTe thin film crystallizes, Cu is expelled from the Ge-Te crystal lattice and precipitates. In this way, it was precipitated
It is thought that Cu changes the reflectance of the reproduction light beam and becomes a noise component, reducing the CNR as described above. Therefore, the present invention has been made with the object of providing an optical information recording medium that has a long life and a high CNR. [Means for Solving the Problems] An optical information recording medium according to the present invention includes 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 a Ge-Te based material to which Cu is added, and a part of the Ge in the optical recording thin film is replaced with Sn. [Operation] As described above, in the optical information recording medium according to the present invention, since a part of Ge in the optical recording thin film is replaced with Sn, the interatomic distance of the Ge(Sn)-Te bond is Ge-
It becomes larger than the Te bond interatomic distance. Therefore, the amount of Cu atoms that can enter the crystal phase GeSnTe lattice increases, and even if the GeSnTe thin film crystallizes, Cu precipitation does not occur, and only the oxidation corrosion resistance improves without reducing the CNR. [Embodiment] FIG. 1 shows an embodiment of an optical information recording medium according to the present invention. That is, 11 is a polycarbonate substrate, on which an optical information thin film is formed.
It has a GeSnTe thin film 12 doped with Cu.
Furthermore, a resin protective film 13 was laminated on the recording thin film to prevent scratches and dust. Here, the substrate 11 is not limited to polycarbonate, and conventionally known transparent resin plates such as PMMA, polyolefin, epoxy, etc., and glass plates can be used. The optical recording thin film 12 is produced by sputtering and vapor deposition. FIG. 2 is a schematic diagram of a sputtering apparatus used when producing the optical recording thin film. Vacuum chamber 21
A rotary substrate support table 2 installed at the top of the
Attach the polycarbonate substrate 11 to the bottom surface of the vacuum chamber 21, evacuate the inside of the vacuum chamber 21 to approximately 5×10 ^-4 Pa, and then introduce active gas such as Ar into the vacuum chamber 21 to increase the gas pressure to 5×10 ^-1 Pa. Make it. In this state, when a high frequency current is simultaneously applied to the alloy target 23 consisting of 30 atomic percent Ge, 20 atomic percent Sn, and 50 atomic percent Te and the Cu target 24, a GeTe thin film doped with Cu is formed on the substrate 11 by the sputtering action. Therefore, some of the Ge in the thin film
Cu-GeSnTe substituted with Sn is formed. At this time, the amount of Sn in the thin film can be adjusted arbitrarily by changing the Sn content in the GeSnTe alloy target 23, and the amount of Cu can be adjusted as desired by changing the Sn content in the GeSnTe alloy target 23.
It can be arbitrarily adjusted by the high frequency power applied to. Another method for adjusting Sn is to use an alloy containing 50 atomic percent Ge and 50 atomic percent Te as a target, place an alloy chip containing 50 atomic percent Sn and 50 atomic percent Te on the target, and perform sputtering. Then,
When obtaining a GeSnTe thin film in which a portion of Ge is replaced with Sn, by increasing or decreasing the number of SnTe alloy chips, the amount of Sn in the GeSnTe thin film can be increased or decreased accordingly. In addition, in order to change the Cu content while keeping the Ge, Sn, and Te contents constant, in addition to the above method, a Cu chip is placed on the GeSnTe alloy target 23 and sputtered to obtain the Cu-added GeSnTe thin film. Cu
Cu was added by increasing or decreasing the number of chips.
The amount of Cu in the GeSnTe thin film can be increased or decreased. Similarly, in the vacuum evaporation method, GeSnTe alloy and
A two-source simultaneous evaporation method using two types of Cu evaporation sources,
A Cu-added GeSnTe thin film can be obtained by adjusting the evaporation rate of the GeSnTe alloy and the evaporation rate of Cu. 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. The resin protective film 13 can be made of not only an ultraviolet curable resin but also a moisture curable resin, a two-component reactive resin, or a solvent-based resin. The disk-shaped optical information recording medium produced in this way was irradiated with laser light to record a signal with a rotation speed of 1800 rpm and a frequency of 1 MHz, and then JISC5024M-1
An accelerated temperature/humidity test was conducted, and the media life was determined from the rate of increase in the bit error rate. Table 1 shows the optical recording film composition, crystallization temperature of the optical recording film, CNR, and medium life of the optical information recording medium according to this example. For comparison, the optical recording composition, optical recording film crystallization temperature, CNR, and medium life of a conventional optical information recording medium whose optical recording film is a GeTe thin film doped with Cu are also shown.

〔effect〕

As explained above, in the optical information recording medium according to the present invention, the optical recording film is made of Cu-doped GeTe
Since the thin film is the main component and a portion of Ge is replaced with Sn, the amount of Cu added can be increased without deteriorating the CNR of the optical information recording medium. It can extend the lifespan.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an embodiment of the optical information recording medium according to the present invention, Fig. 2 is a schematic diagram of a sputtering device applicable to the present invention, and Fig. 3 is a diagram for explaining its characteristics. . DESCRIPTION OF SYMBOLS 11... Substrate, 12... Optical recording thin film, 13... Resin protective film, 21... Vacuum chamber, 22... Substrate support table,
23...GeSnTe target, 24...Cu target.

Claims (1)

[Claims] 1. 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 thin film, the main component of the optical recording thin film is a Cu-added Ge-Te based material. . An optical information recording medium, characterized in that a portion of Ge in the optical recording thin film is replaced with Sn.