JPH02147388A - Information recording medium - Google Patents

Abstract

PURPOSE:To contrive higher C/N by providing a substrate and a recording film thereon comprising an Au-Te alloy, carbon and fluorine for recording information by irradiation with a laser light. CONSTITUTION:An information recording medium 18 comprises a substrate and a recording film 14 provided thereon. The recording film 14 comprises an Au-Te alloy, carbon and fluorine, with the Au content being 2-47atom%. This construction enables pit formation at a melting temperature approximate to or lower than the melting point of Te, and ensures uniformity of pit size. Therefore, 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 made of Te.

It is known that it contains C and H, and at least C and H form a chemical bond.

This recording film cannot be formed even if it is attempted to be formed by vapor deposition using Te and hydrocarbon as sources (without using plasma), following the Te film, and 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 become large and the shape becomes irregular when the writing laser power exceeds the recording threshold.
) There was a problem in that the 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 Problem) In order to achieve the above object, the present invention includes a substrate, a substrate formed on the substrate, and information recorded by irradiation with a laser beam.
Au X Te too-x (2≦x≦47 atomic%
) alloy and a recording film containing carbon and fluorine.

(Function) According to the present invention, since it is possible to change the recording film/substrate interfacial tension compared to conventional recording films, it is possible to reduce the diameter of the bit and make it uniform. Therefore, 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 the information recording medium of the present invention. The information recording medium 18 of the present invention has a substrate 1
3 and a recording film 14 laminated on this 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 and fluorine.

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

As already known, according to the phase diagram of the Au-Te binary system, if the amount of Au added is up to 47 at%, Te
It has a melting point slightly above or below the melting point of

Simply put, the range below the melting point of Te is 2 atomic % to Au
Although the amount is 20 atomic %, the addition of T e E A u causes 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.%.

In a recording film in which Au is added to Te in an amount exceeding 47 atomic %, the melting point is considerably higher than the melting point of Te, and the recording sensitivity by laser light is deteriorated, which is not preferable.

That is, in the present invention, the same degree of Te 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, 1000
The thickness is preferably 500 angstroms or less, and more preferably 500 angstroms or less.
The thickness is preferably 100 to 300 angstroms or less.

As shown in Figure 2, this has a pulse width of 60 n5ecs.
Linear speed 5. This is also clear from the writing sensitivity characteristics when the laser is incident through the PC board under the condition of 5 m /see. Further, if the thickness is less than 100 angstroms, the recording film becomes discontinuous and the probability of forming pinholes increases, which is not preferable. In the case of heat mode recording, this pinhole may be mistaken for an original bit during readout, and may also trigger 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 reproducing laser light used to read information recorded in bits is normally continuously oscillated. In order to read out information with a good S/N ratio in this state, it is also necessary to increase the reproduction laser power. However, if a certain threshold is exceeded, bits (information) may be destroyed and the level of reproduced reflected light may decrease.

Therefore, the track was continuously held at a linear velocity of 5.5 cm/see, the reproduction laser power was varied, and changes in the reflected light level were observed using a synchroscope.

The observation results are shown in Figure 3J0 According to the observation results, no matter the thickness of the recording film,
With a laser power of 0.6 or 0.8 ■W, the level of reflected light did not change for 3 hours.

However, when the power was increased to 1W, 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 set at 0.5 ■W. The maximum allowable reproduction laser power P■aX (■W) is Psa
x=0.2+0.05Vt' is given. Here, V is the linear velocity (m/see) of the recording medium. Also, P
It is required that the level of reflected light does not change even after 10 cycles of continuous playback with laX, but this must not change for at least 1 hour when the rotation speed is 180 orpm and the linear velocity is 5°5 s/see. This means that it will not happen. Therefore, in the recording film 14 of the present invention, even with a power of 0.8 .mu.W under the above conditions, no change occurs for up to 3 hours, which fully satisfies this requirement.

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 14 of the present invention. First, open the valve 2 of this sputtering device to the rotary pump 3 side and apply 0.2T inside the chamber 1.
Exhausted to orr. Next, the valve 2 was opened to the cryopump 5 side, and the temperature was evacuated to 1×10 −′ Torr or less.

At this time, since there was no need to control the displacement, the conductance valve 4 was left fully open.

Next, the valve 6 was opened, and 1108 CC of Ar gas was introduced into the chamber 1 from the Ar gas line 7 while being controlled by 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, the Au-Te alloy target 9 (diameter 5 inches; composition is Au + □Te as ; atomic %) I;:DC
Apply 100W from power supply 10, shutter 1
1 was closed and sputter discharge was performed for 5 minutes to perform sputter cleaning.

After stopping the supply of Ar gas and the supply of DC power, the inside of the chamber 1 was once
-'Torr or less. After that, open valves 6 and 17 to introduce Ar gas and CiF's gas into chamber 1.
While adjusting with a mass flow controller (not shown) through r gas line 7 and C, F8 gas line 8, IO8
CCM was introduced one by one. Then, using the conductance valve 4, the pressure inside the chamber 1 is reduced to 5 x 10-' Torr.
was controlled.

After confirming that there was no pressure fluctuation, 100 W was applied to the AUTE target 9 from the DC power supply 10 to cause sputter discharge. After confirming that the discharge is stable, the shutter 11 is opened and the recording film 1 containing AuTe alloy and carbon and fluorine is deposited on the polycarbonate (PC) substrate 13 that has been set in advance on the rotor 12.
The rotor laminated with 4 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×10-' Torr using the cryopump 5.
Exhausted to below. Next, the valve 15 was opened, N2 gas was introduced into the chamber 1 from the N2 gas line 16, the pressure was returned to atmospheric pressure, and the medium 18 was taken out, thereby forming the information recording medium 18 shown in FIG. 1.

As a result of X-ray diffraction analysis, it was confirmed that the recording film 14 thus formed was an amorphous film in which no diffraction peak was observed from a specific diffraction angle. This amorphous film is
Unlike polycrystals, there are no grain boundaries, so the reproduced laser light is not modulated at the grain boundaries and does not generate grain boundary noise.

Example 2 In the information recording medium 18 manufactured by the method shown in Example 1, 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. Under accelerated conditions of 75°C-90%,
After the information recording medium containing the Te film and the Te-C film having the same film thickness as shown in Example 1 and the recording film 14 of the present invention was alerted for a certain period of time, writing was performed and the error rate was measured. 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 the recording film of the present invention was an amorphous film even when subjected to X-ray diffraction analysis after this measurement.

Figure 6 shows a pulse width of 50 n5ecs and a writing frequency of 37.
A GaAs-based semiconductor laser with a MH2% wavelength of 830 ns was used, an objective lens numerical aperture (NA) of 0.52, and a linear velocity of 5.
C/N (Carrier
/Nolse) ratio. This result shows that the recording film of the present invention has higher sensitivity than the conventional Te-C film.

Example 3 When sputtering an AuTe alloy target using only fluorocarbon gas, there are the following two drawbacks.

1) A recording film obtained by sputtering an AuTe alloy target in a 100% fluorocarbon gas atmosphere has a small optical absorption coefficient (absorption rate).

For this reason, in the case of a heat mode recording method in which information is recorded by forming bits using heat generated when laser light is absorbed, a decrease in recording sensitivity is observed.

2) During sputtering of an AuTe alloy target, carbon powder, which is considered to be a decomposition product of fluorocarbon gas, is noticeably deposited on the target surface. Therefore, if sputtering is performed continuously for a long period of time, there is a possibility that the sputtering film formation rate will decrease.

Here, the flow rate of fluorocarbon gas is X1, the flow rate of desired gas is Y, and the gas flow rate ratio is Q-(X/(X0Y))x1
Defined as 00%, Q-30°50.60 and 100%
As a result of investigating the write sensitivity characteristics of a recording film (film thickness 250 angstroms, composition Au, 2Te, etc.) formed according to each gas flow rate ratio (using C3F8 gas and argon gas), the results are as shown in Fig. 7. I was able to get good results. When detecting this sensitivity characteristic, the rotation speed is 1850
The rp pulse width was 60 n5ec. This detection result shows that in the case of Q-100%, the laser power required to obtain a constant reproduced signal amplitude is larger than in the case of other Q values, and the writing sensitivity is deteriorated. In addition, regarding the state of the target surface under each Q value, the case of Q-100% was the most blackened and had a large amount of deposits. As the Q value decreased, the percentage of deposits tended to decrease. FIG. 8 shows the results of measuring error rates under the same recording conditions as in FIG. 5 for recording films formed under various Q values under the same conditions as in FIG. 7. Therefore, it can be seen from the results of FIGS. 7 and 8 that the sputtering condition Q is preferably 5≦Q≦50%.

Example 4 FIG. 9 shows the effect of the gas flow rate ratio Q on the sputtering rate. If sputtering is continued under the condition that Q-50% (gases are C, F, gas and argon gas, CsFg gas flow rate exceeds 10108 CC), the sputtering rate decreases. In Figs. 9 and 10, The sputtering rate is normalized with the first value as 1. Figure 10 shows the same flow rate ratio (Q-50%) but the fluorocarbon gas C
Cs Fs gas) flow rate to 10.20 and 11005C.
The sputtering rate when C is shown. As the flow rate increased, the amount of deposits on the target surface tended to increase. Therefore, the flow rate ratio of fluorocarbon gas is IO8
It can be seen that CCM or less is preferable.

In this example, fluorocarbon gas (Ci
Au T under a mixed atmosphere of Fs) and rare gas (argon)
Although the e-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 explained above, according to the present invention, it is possible to provide an information recording medium that can perform high-density recording with a high CZN ratio.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an information recording medium showing an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between recording film thickness and writing sensitivity.
Fig. 3 is a diagram showing changes in reproduction time and reflection level, Fig. 4 is a diagram showing a sputtering apparatus for manufacturing the information recording medium shown in Fig. 1, and Fig. 5 is a diagram showing the error rate of the recording film after undergoing acceleration conditions. Figure 6 is a diagram showing the recording sensitivity of the recording film, Figure 7 is a diagram showing the relationship between writing laser power and modulation degree for each gas flow rate ratio, and Figure 8 is a diagram showing the acceleration time for each gas flow rate ratio. Figure 9 is a diagram showing the relationship between the error rate and error rate, Figure 9 is a diagram showing changes in sputtering rate for each gas flow rate ratio,
The figure is a diagram showing changes in sputtering rate for each fluorocarbon gas flow rate. 13... Substrate 14... Recording film 18... Information recording medium

Claims (1)

[Claims] (1) A substrate, Au_xTe_1_0_0_-_x(2≦x
≦47 atomic %) alloy, and a recording film containing carbon and fluorine.