JPH02147391A - Information recording medium - Google Patents

Abstract

PURPOSE:To obtain high C/N by providing a recording film comprising an Au-Te alloy, carbon, nitrogen, fluorine and hydrogen to record information therein by irradiation with a laser light, on a substrate. CONSTITUTION:A substrate 13 is formed from a material which is transparent to a laser light with which an information recording medium is irradiated for recording and reproduction of information. For instance, when the laser light has an oscillation wavelength in the vicinity of the near infrared region, a polycarbonate, polymethyl methacrylate or the like is used as the material. A recording film 14 comprises an Au-Te alloy, with carbon, nitrogen, fluorine and hydrogen contained therein. For formation of pits at a melting temperature approximate to or lower than the melting point of Te, uniformity of pit size, formation of less rim parts and an increase in recording density, the Au content is set in the range of 2-47atom%. This construction makes aperture diameters of pits smaller and uniform, so that a high C/N can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an information recording medium on which information is recorded and reproduced by, for example, irradiation with laser light.

(Prior Art) As a type of information recording medium, information is recorded by irradiation with laser light and the recorded information is reproduced.
A device equipped with a recording film containing Te as a main component has been developed. Furthermore, a recording film containing carbon and hydrogen in addition to the Te-based recording film has been developed and put into practical use (see Japanese Patent Laid-Open No. 58-9234).

When creating this recording film, Te is sputtered in an atmosphere containing hydrocarbon gas. Then, a film of simple Te (T
A recording film (
A Te-C film (hereinafter referred to as Te-C film) is obtained. This recording film is an amorphous film and contains Te1C and H, and it is known that at least C and H are chemically bonded.

This recording film cannot be formed by vapor deposition using Te and hydrocarbon as sources (without using plasma), as in the Te film, but can only be obtained by using plasma. This is because a film is formed by a chemical reaction between C and H after the hydrocarbon gas is once decomposed in plasma, and this is a major feature when forming an optical recording film.

(Problem to be Solved by the Invention) However, in the Te-C film, the pits open widely and become irregular in shape when the writing laser power exceeds the recording threshold.
There was a problem that the se) ratio suddenly decreased.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide an information recording medium that can obtain a high C/N ratio.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention includes a substrate, and an Au g Te 100 film formed on the substrate and on which information is recorded by irradiation with a laser beam. -X (2≦x≦47 atomic %) alloy and a recording film containing carbon, nitrogen, fluorine, and hydrogen.

(Function) In the information recording medium of the present invention, since the recording film is sputtered in a hydrocarbon atmosphere, it has excellent oxidation resistance. In addition, the laser light absorbing substance in the C-H matrix is
Since Au Te was used from e, the melting point changed from 450°C to 35°C.
The temperature drops to 0°C, making it possible to record with high sensitivity even with low power. Further, in the information recording medium of the present invention, the diameter of the bits is small and uniformly arranged, so that a high C/N ratio can be obtained.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing the structure of an information recording medium 18 of the present invention. The information recording medium 18 of the present invention is composed of a substrate 13 and a recording film 14 laminated on the substrate 13.

The substrate 13 is made of a material that is transparent to laser light that is irradiated onto the information recording medium for recording and reproducing information. For example, when using a laser beam having an oscillation wavelength near infrared, polycarbonate (PC), polymethyl methacrylate (PMMA), glass, polyolefin, epoxy resin, etc. are used.

The recording film 14 is made of an Au-Te alloy containing carbon, nitrogen, fluorine, and hydrogen.

Au z Te in the present invention. The composition ratio of the ox alloy will be explained.

As is already known, according to the phase diagram of the Au-Te binary system, if the amount of Au added is up to 47 at %, the melting point will be slightly higher than or lower than the melting point of Te. Simply,
The range below the melting point of Te is 2 at% to 20 at% of Au.
However, by adding Tel, :AU, there will be a change in the way the rim is formed during bit formation. As a result of this change, it was found that a clean rim was formed when the Au content was in the range of 2 at.% to 47 at.%. Furthermore, in a recording film in which Al is added to Te in an amount exceeding 47 atomic %, the temperature becomes considerably higher than the melting point of Te, which is undesirable because the recording sensitivity with laser light deteriorates.

That is, in the present invention, the same degree of sTe or T
In order to obtain effects such as forming bits with a melting point lower than that of e, and increasing the recording density by making the bits uniform in size and reducing the rim portion, the Au content should be between 2 at.% and 47 at. % range.

Furthermore, if the thickness of the recording film 14 is 1000 angstroms or more, the writing sensitivity will decrease.

Therefore, it is preferably 1000 angstroms or less, but 500 angstroms or less, more preferably 10
A thickness of 0 to 300 angstroms is preferable.

For example, as shown in FIG. 2, the pulse width is 6On5.
ecs linear velocity5. This is also clear from the writing sensitivity characteristics when the laser is incident through the PC board under the condition of 5i/see. Further, if the thickness is less than 100 angstroms, the recording film becomes discontinuous and the probability of pinhole formation increases, which is not preferable. In the case of heat mode recording, this pinhole may be mistaken for an original bit during reading. Furthermore, it also serves as a trigger for oxidation of the recording film.

Next, the tolerance of the reproduction laser power (the power level at which reproduction can be performed without causing deterioration of the recording film) of the information recording medium 18 shown in FIG. 1 will be explained. The reproduction laser light used to read information recorded in bits is normally continuously oscillated. In this state, in order to read information with a good S/N ratio, it is necessary to increase the reproduction laser power, but if it exceeds a certain threshold, the pits (information) will be destroyed and the level of the reproduction reflected light will decrease. There is. Therefore, the linear speed is 55
The track of m+/see was held continuously, the reproduction laser power was changed, and changes in the reflected light level were observed using a synchroscope. The observation results are shown in Figure 3.

According to these observation results, for any recording film thickness,
When the laser power was 0.6 or 0.8 mW, the level of reflected light did not change for 3 hours.

However, when the power was increased to 1 mW, the level of reflected light decreased within several hours. In this case, the smaller the film thickness, the greater the degree of decrease. The level of reflected light is normalized with the level immediately after reproduction set at 1.

The allowable playback power of the write-once recording film, which is currently being standardized, is a linear velocity of 5.5 ■/see at a rotational speed of 180 orpm.
In this case, the maximum power is determined to be 0.5 mW. The maximum allowable reproduction laser power Pmax (sW) is Pmax
It is given by x-0,2+0.055V. Here, V is the linear velocity (5ee) of the recording medium. In addition, it is required that the level of reflected light does not change even after 105 cycles of continuous playback with P■aX, which requires a rotation speed of 180.
Orpm ・At least 1 for linear speed 55m/see
This means that it should not change over time. Therefore, in the information recording medium of the present invention, 0.8 mW under these conditions
Since no change occurs even with the power of 3 hours, this requirement is fully met.

Example 1 A method for forming the information recording medium 18 shown in FIG. 1 will be described.

FIG. 4 is a schematic diagram of a sputtering apparatus for forming the recording film of the present invention. First, open the valve 2 of this sputtering device to the rotary pump 3 side and set the inside of the chamber 1 to 0.2 Torr.
Exhausted to r. Next, the valve 2 was opened to the cryopump 5 side, and the temperature was evacuated to below 1xlO-'Torr. Since there was no need to control the ζ displacement at this time, the conductance valve 4 was left fully open.

Next, the valve 6 was opened, and IOSCCM was introduced into the chamber 1 while adjusting Ar gas from the Ar gas line 7 using a mass flow controller (not shown). Next, while monitoring the pressure inside the chamber 1 with an ion gauge (not shown), the conductance valve 4
Adjusted to orr. After confirming that this pressure does not fluctuate, DC
Apply 100W from power supply 10, shutter 1
1 was closed and sputter discharge was performed for 5 minutes to perform sputter cleaning.

A: After stopping the gas supply and DC power supply, use the cryopump 5 to temporarily pump the inside of the chamber 1 to I
It was evacuated to -5 Torr or less. After that, open valves 6, 17, and 25 to fill chamber 1 with Ar gas, CH4 gas, and N gas.
F, gas was introduced at 10.10 and 5 SCCM through Ar gas line 7, CH4 gas line 8, and NF gas line 26 while being controlled by a mass blow controller (not shown), respectively. Then, using the conductance valve 4, the pressure inside the chamber 1 is reduced to 5 x 10-3 Torr.
was controlled. After confirming that there is no pressure fluctuation, the AuT
eTarget91. : 100 W was applied from the DC power supply 10 to cause sputter discharge. After confirming that the discharge is stable, open the shutter 11 and remove the polycarbonate (P) that was previously set on the rotor 12.
C) A recording film 14 containing an AuTe alloy and carbon and hydrogen was laminated on the substrate 13. The rotor was rotated at 60 rpm. When the film thickness reached 250 angstroms, the shutter was closed and power supply was stopped. Next, the conductance valve 4 is fully opened, and the inside of the chamber 1 is heated to I x 10-' Torr using the cryopump 5.
Exhausted to below. Next, the valve 15 is opened, N2 gas is introduced into the chamber 1 from the N2 gas line 16, the pressure is returned to atmospheric pressure, and the medium 18 is taken out, thereby forming the information recording medium 18 shown in FIG. did it.

As a result of X-ray diffraction analysis, it was confirmed that the information recording medium 18 thus formed was an amorphous film in which no diffraction peak was observed from a specific diffraction angle. Unlike a polycrystalline film, an amorphous film does not have grain boundaries, so that reproduction laser light is not modulated at the grain boundaries and does not generate grain boundary noise.

Example 2 Information recording medium 1 manufactured by the method shown in Example 1
In No. 8, the ratio of read errors (error rate) occurring as a result of surface roughness due to oxidation, which is an index of oxidation resistance, was analyzed. After leaving the information recording medium containing the Te film and Te-C film of the same film thickness as shown in Example 1 and the recording film 14 of the present invention for a certain period of time under accelerated conditions of 75°C = 90%. , and measured the error rate. The results are shown in FIG. The error rate was normalized with the value before being placed under acceleration conditions as 1.

According to this figure, the error rate of the Te film increases in just a few days. The Te-C film also gradually increases after 100 hours. On the other hand, the recording film 14 of the present invention showed almost no change even after being left for 1000 hours. Therefore, it can be seen that it has good oxidation resistance even under high temperature and high humidity conditions and has a long life.

Note that this recording film 14 was also found to be an amorphous film when subjected to X-ray diffraction analysis after this measurement.

Figure 6 shows a pulse width of 50 n5ec and a writing frequency of 37
Using a GaAs-based semiconductor laser with a MH2% wavelength of 830 nm, the numerical aperture (NA) of the objective lens was 0.52, and the linear velocity was 5.
．． C/N under the condition of 511/see (Carrler
/Nolse) ratio. This result shows that the recording film of the present invention has even higher sensitivity than the conventional recording film.

Example 3 A film was formed using the apparatus shown in FIG. 4 using the same procedure as in Example 1, except that benzene gas was used instead of CH4 gas and NF and gas were not used. , as shown in FIG.
An information recording medium 118 in which 250 recording films 114 containing Bss gold alloys C and H were laminated was obtained.

The writing sensitivity characteristics, reproduction laser power tolerance, error rate, and C/N ratio of this recording film were determined in the second, third, and fifth tests, respectively.
And when examined under the same conditions as in Fig. 6, Nos. 8 and 9
, results similar to those shown in FIGS. 10 and 11 were obtained.

Therefore, it can be seen that even if the AuTe alloy is sputtered in an atmosphere containing a hydrocarbon gas having a benzene ring, a recording film having good recording properties can be obtained.

In this example, hydrocarbon gas (methane) and N
Au in a mixed atmosphere of F gas and rare gas (argon)
Although the Te target was sputter discharged, the discharge may be performed in an atmosphere that does not contain a rare gas.

Further, in this embodiment, a transparent organic resin substrate is used, but the substrate may be opaque when the writing and reproducing laser beams are made incident from the recording film side without passing through the substrate.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an information recording medium that exhibits excellent oxidation resistance even in a high temperature and high humidity environment, has a long life, and has a highly sensitive recording film.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an information recording medium according to an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between recording film thickness and writing sensitivity, and FIG.
The figure shows changes in playback time and reflection level, Figure 4 shows a sputtering apparatus for manufacturing the information recording medium shown in Figure 1, and Figure 5 shows the error rate of the recording film under acceleration conditions. Figure 6 is a diagram showing the recording sensitivity of the recording film, Figure 7 is a diagram showing the recording sensitivity of the recording film.
The figure is a sectional view of an information recording medium according to another embodiment of the present invention.
FIG. 8 is a diagram showing the relationship between recording film thickness and writing sensitivity according to another embodiment of the present invention, FIG. 9 is a diagram showing changes in playback time and reflection level, and FIG. 10 is a diagram showing changes in recording film thickness and writing sensitivity according to another embodiment of the present invention. FIG. 11 is a diagram showing the error rate of a recording film, and is a diagram showing the recording sensitivity of a conventional recording film and a recording film according to another embodiment of the present invention. 13, 113 ... Substrate 14° Recording film 18° Information recording medium

Claims (1)

[Claims] A substrate; Au_xTe_1_0_0_-_x (2≦x
≦47 atomic %) alloy, and a recording film containing carbon, nitrogen, fluorine, and hydrogen.