JP2558844B2 - Information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention is to write information by forming pits by irradiation of laser light, and to change the information by changing the amplitude of laser light by the pits. The present invention relates to an information recording medium for reading data.

(Prior Art) Information is recorded by irradiation with a laser beam, and as a kind of information recording medium on which the recorded information is reproduced, one having a recording film containing Te as a main component has been developed. . Further, a recording film containing carbon and hydrogen in the recording film containing Te as a main component has been developed and put into practical use (see Japanese Patent Laid-Open No. 58-9234).

When forming this recording film, tellurium (Te) is sputtered in an atmosphere containing a hydrocarbon gas. Then, a recording film (hereinafter referred to as a Te-C film) having higher sensitivity and excellent oxidation resistance than a film of Te alone (Te film) can be obtained. This recording film is an amorphous film, contains Te, C and H, and it is known that at least C and H are chemically bonded.

This recording film cannot be formed even if it is attempted to be formed by vapor deposition (without using plasma) using Te and hydrocarbon as a source after the Te film, and it is obtained only by using plasma. This is because after the hydrocarbon gas is once decomposed in plasma, C and H undergo a chemical reaction to form a film, which is a major feature when forming an optical recording film.

(Problems to be Solved by the Invention) When a recording film made of Te and a hydrocarbon as described above and a recording film formed of Te are compared under high temperature and high humidity of 65 ° C.-90% (accelerated condition), The Te film was oxidized within 1 week to impair the optical recording performance, whereas the Te-C film was stable even after 1 month without being oxidized to the inside of the film. However, the Te-C film also has a problem that the recording film is crystallized at a high temperature (about 75 ° C. or higher), so that the surface is roughened, the noise is increased, and the influence on the reproduction signal is increased. .

In order to solve the above problems, it is an object of the present invention to provide an information recording medium having a long life, the surface of which is not easily roughened even in an environment of high temperature and high humidity.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a substrate and an Ag-Te alloy which is formed on the substrate and records information by laser light irradiation. And an amorphous recording film containing carbon and hydrogen.

(Operation) The optical recording film of the present invention is made of AgTe alloy so that the surface state can be stably maintained even at high temperature. In the present invention, by including a recording film containing an Ag-Te alloy and carbon and hydrogen, an information recording medium that maintains stable recorded information even under high temperature and high humidity and has excellent recording sensitivity Can be provided. Hereinafter, the recording film of the present invention will be referred to as "AgTe-C film" for convenience.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view schematically showing the structure of the information recording medium of the present invention. The information recording medium of the present invention comprises 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 the laser light emitted onto the information recording medium for recording and reproducing information. For example, when using a laser beam having an oscillation wavelength in the near-infrared region, polycarbonate (PC), polymethylmethacrylate (PMMA), glass, polyolefin, epoxy resin and the like are used.

The recording film 14 is made of Ag-Te alloy containing carbon and hydrogen.

Next, the composition ratio of the Ag—Te alloy in the recording film 14 will be described.

According to the already known phase diagram of the Ag-Te binary system (Fig. 2), Ag ₂ Te and Ag ₃ Te ₂ exist as intermetallic compounds. However, these compounds have melting points of 959 each.
It is much higher than that of Te alone (450 ℃) at ℃ and 700 ℃, so it is not very practical in the heat mode recording method that melts the recording film to form pits.

However, the melting points of Ag ₃₃ Te ₆₇ exhibiting a eutectic point and those having a composition ratio in the vicinity thereof have a lower melting point (351 to 449 ° C.) than Te. Therefore, the content ratio of Ag is preferably 2 to 55 at%. With this composition ratio, since the melting point is lower than that of Te, recording can be performed with higher sensitivity than that of the Te film. Further, when Ag is added, it is possible to obtain effects such that the pit sizes are uniform, the rim portion is reduced, and the recording density is increased.

If the thickness of the AgTe-C recording film 14 is 1000 Å or more, the writing sensitivity is lowered. Therefore, the thickness is preferably 500 Å or less, more preferably 100 to 300 Å. This is also clear from the write sensitivity characteristics when a laser is incident through a PC substrate under the conditions of a pulse width of 60 nsec and a linear velocity of 5.5 m / sec as shown in FIG. On the other hand, if it is 100 Å or less, 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 is not preferable because it may be mistaken for the original pit at the time of reading, and it is also a trigger for oxidation of the recording film, so it should be minimized.

Next, the tolerance of the reproduction laser power in the information recording medium shown in FIG. 1 (power level at which reproduction can be performed without causing deterioration of the recording film) will be described. The reproducing laser light for reading the information recorded in the pit is usually continuously oscillated. In order to read information with a good S / N ratio in this state, it is necessary to increase the reproduction laser power as well.
If it exceeds a certain threshold value, the pit (information) may be destroyed, and the level of the reflected light for reproduction may decrease. Then the linear velocity is 5.5m / sec
Was continuously held on the track, and the reproducing laser power was changed to observe the change in the reflected light level with a synchroscope. The observation results are shown in FIG.

According to this observation result, the AgTe-C film of any film thickness is 0.
With a laser power of 6 or 0.8 mW, the level of reflected light did not change for 3 hours. However, when the power was set to 1 mW, the level of reflected light decreased within a few hours. In this case, the smaller the film thickness, the greater the degree of decrease. The level of reflected light is standardized with 1 immediately after reproduction.

The allowable reproduction power of the write-once recording film, which is being standardized at present, is determined to be 0.5 mW at the maximum at a rotation speed of 1800 rpm and a linear velocity of 5.5 m / sec. The maximum allowable reproduction laser power Pmax (mW) is given by Pmax = 0.2 + 0.055V. Here, V is the linear velocity (m / sec) of the recording medium, and Pmax
It is required that the level of reflected light does not change even after continuously reproducing for 10 ⁵ cycles at 1800 rpm.
・ In case of linear velocity of 5.5m / sec, it should not change for at least 1 hour. Therefore, under the above conditions, the recording film 14 of the present invention does not change even at a power of 0.8 mW for up to 3 hours.
Will meet that need well.

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

FIG. 5 is a schematic view of a sputtering apparatus for forming the recording film of the present invention. First, the valve 2 of this sputtering apparatus was opened to the rotary pump 3 side, and the chamber 1 was evacuated to 0.2 Torr. Next, the valve 2 was opened to the side of the cryopump ^{5 and} exhausted to 1 × 10 ⁻⁵ Torr or less. At this time, since it is not necessary to control the exhaust amount, the conductance valve 4 was fully opened.

Next, open the valve 6 and adjust the Ar gas from the Ar gas line 7 with a mass flow controller (not shown),
Introduced 10 SCCM into chamber 1. Next, while monitoring the pressure inside the chamber 1 with an ion gauge (not shown),
The conductance valve 4 was adjusted to 5 × 10 ⁻³ Torr. After confirming that this pressure does not fluctuate, the Ag-Te alloy target 9 (diameter 5 inches: composition is Ag ₃₃ Te ₆₇ ; at%)
100 W was applied from the C power supply 10 and sputter discharge was performed for 5 minutes with the shutter 11 closed to perform sputter cleaning.

After stopping the supply of Ar gas and the supply of DC power, the interior of the chamber 1 was once evacuated to 1 × 10 ⁻⁵ Torr or less using the cryopump 5. Then open valves 6 and 17 to open chamber 1.
Mass flow controller (not shown) in which Ar and CH ₄ gas are passed through Ar gas line 7 and CH ₄ gas line 8, respectively.
Introduced 10 SCCM each while adjusting. Then, using the conductance valve 4, the pressure in the chamber 1 is adjusted to 5 × 10 ^-3 To
Controlled to rr. After confirming that there is no pressure fluctuation, AgTe
Apply 100W from the DC power supply 10 to the target 9,
It was sputtered. After confirming that the discharge is stable, the shutter 11 is opened, and the recording film 14 containing AgTe alloy and carbon and hydrogen is placed on the polycarbonate (PC) substrate 13 which is set in advance on the rotor 12. Laminated. Rotor is 60
Rotated at rpm. When the film thickness reached 250Å, the shutter was closed and the power supply was stopped. Next, the conductance valve 4 was fully opened, and the interior of the chamber 1 was evacuated to 1 × 10 ⁻⁵ Torr or less using the cryopump 5. Then opening the valve 15, after returning to atmospheric pressure by introducing the N ₂ gas line 16 the N ₂ gas into the chamber 1, by taking out the medium 18, the information recording medium shown in Figure 1 is formed .

As a result of X-ray diffraction analysis, it was confirmed that the recording film 14 thus obtained was an amorphous film in which no diffraction peak from a specific diffraction angle was observed. Unlike the polycrystalline film, the amorphous film has no crystal grain boundary, and therefore reproduction laser light is not modulated at the grain boundary portion to cause grain boundary noise.

Example 2 Information recording medium manufactured by the method shown in Example 1
In 18, the ratio of read errors (error rate) resulting from surface roughness due to oxidation, which is an index of oxidation resistance, was analyzed. Example 1 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 (4) and the recording film 14 of the present invention was left for a certain period of time, writing was performed and the error rate was measured. The result is shown in FIG. The error rate was standardized with a value of 1 before being placed under accelerated conditions. According to this figure, the error rate of the Te film increased in just a few days. Te-C film also
It has been gradually increasing after 100 hours. On the other hand, the AgT of the present invention
The e-C film showed almost no change when left for 1000 hours. Therefore, it can be seen that the AgTe-C film has good oxidation resistance even under high temperature and high humidity and has a long life. The AgTe-C film was an amorphous film when X-ray diffraction analysis was performed after this measurement.

Fig. 7 shows a Te-C film under the conditions of a pulse width of 50 nsec, a writing frequency of 3.7 MHz, a wavelength of 830 nm, and a GaAs semiconductor laser with a numerical aperture (NA) of the objective lens of 0.52 and a linear velocity of 5.5 m / sec.
It shows the magnitude of C / N (Carrier / Noise) when written in the AgTe-C film. From this, the AgTe-C film of the present invention is
It can be seen that the sensitivity is higher than that of the conventional Te-C film.

Example 3 When an AgTe alloy target is sputtered in a rare gas and a hydrocarbon gas or a hydrocarbon gas, the composition of the AgTe alloy in the recording film may not be equal to the composition of the AgTe alloy target, and Te may increase in the recording film. is there. Therefore, the apparatus shown in FIG. 2 was used to form a film under the same conditions as in Example 1 except that the composition of the AgTe alloy target was changed, and the relationship between the composition of the AgTe alloy target and the composition of the AgTe alloy in the recording film. Was investigated by ICP (Inductively Coupled Plasma Emission Spectroscopy). The detection result is shown in FIG. From the figure, the AgTe of the recording film 14 is
It can be seen that the composition tends to have 10% more Te than the composition of the target. Therefore, when obtaining a recording film having a composition of eutectic point (Ag ₃₃ Te ₆₇ ), it is desirable to use a target having a composition of about Ag ₄₅ Te ₅₅ .

Example 4 When an AgTe alloy target is sputtered with a hydrocarbon gas only, there are the following two drawbacks.

1) A recording film obtained by sputtering an AgTe alloy target in an atmosphere of 100% hydrocarbon gas has a small optical absorption coefficient (absorption rate). Therefore, in the case of the heat mode recording system in which pits are formed by heat generated when the laser light is absorbed to record information, it is recognized that the recording sensitivity is low.

2) During sputtering of an AgTe alloy target, carbon powder, which is considered to be a decomposition product of hydrocarbon gas, is significantly deposited on the target surface. Therefore, continuous sputtering for a long time may reduce the sputtering film formation rate. This is a major drawback in production.

Here, the flow rate of the hydrocarbon gas is X, the flow rate of the rare gas is Y, and the gas flow rate ratio is defined as Q = {X / (X + Y)} × 100%, and Q = 30,50,60 and 100% AgTe- film formed according to each gas flow rate ratio (using methane gas and argon gas)
As a result of examining the writing sensitivity characteristic of the C film (film thickness 250 Å, composition Ag ₃₃ Te ₆₇ ), the result as shown in FIG. 9 could be obtained. When detecting this sensitivity characteristic, the rotation speed is 1850rp
The pulse width was m and the pulse width was 60 nsec. From this detection result, Q = 1
In the case of 00%, it can be seen that the laser power required to obtain a constant reproduced signal amplitude is larger than that of other Q values and the writing sensitivity is deteriorated. Further, the state of the target surface under each Q value was the most blackened when Q = 100%, and there were many deposits. The proportion of deposits tended to decrease as the Q value decreased. FIG. 10 shows the recording film formed under various Q values under the same conditions as in FIG.
The results of measuring the error rate under the same acceleration conditions as the figure are shown. Therefore, it can be seen from the results of FIGS. 9 and 10 that the sputtering condition Q is preferably 5 ≦ Q ≦ 50%.

Example 5 FIG. 11 shows the effect of the gas flow rate ratio Q on the sputter rate. If the sputtering is continued under the condition of Q = 50% (gas is methane gas and argon gas, the flow rate of methane gas is 10 SCCM), the sputter rate decreases. In FIGS. 11 and 12, the sputter rate is the first
The value of the second time is standardized as 1. FIG. 12 shows the sputter rate when the flow rate of hydrocarbon gas (CH ₄ gas) was set to 10, 20 and 100 SCCM while maintaining the same flow rate ratio (Q = 50%). When the flow rate increased, the amount of deposits on the target surface tended to increase. Therefore, it is understood that the flow rate of hydrocarbon gas is preferably 10 SCCM or less.

In the present embodiment, the AgTe target was sputter-discharged in a mixed atmosphere of hydrocarbon gas (methane) and rare gas (argon), but it may be discharged in an atmosphere of only hydrocarbon gas.

Further, although the transparent organic resin substrate is used in this embodiment, the substrate may be opaque when the writing and reproducing laser light is incident from the recording film surface side without dropping the substrate.

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

[Brief description of drawings]

FIG. 1 is a sectional view of an information recording medium according to an embodiment of the present invention, FIG. 2 is a state diagram of Ag—Te, and FIG. 3 is a diagram showing a relation between a film thickness of an AgTe—C film and a writing sensitivity. FIG. 4 is a diagram showing changes in reproduction time and reflection level, FIG. 5 is an optical recording film forming apparatus according to one embodiment of the present invention, and FIG. 6 is a diagram showing error rates of recording films subjected to acceleration conditions. 7 is a diagram showing the recording sensitivity of the Te-C film and the AgTe-C film, FIG. 8 is a diagram showing the relationship between the composition of the AgTe alloy target and the composition of the AgTe alloy in the recording film, and FIG. 9 is each gas flow rate. FIG. 10 is a diagram showing the relationship between the writing laser power and the modulation factor for the ratio, FIG. 10 is a diagram showing the relationship between the acceleration time and the error rate for each gas flow rate ratio, and FIG. 11 is a change in the sputter rate for each gas flow rate ratio. Showing the figure, and
FIG. 12 is a view showing changes in the sputter rate with respect to each hydrocarbon gas flow rate. 1 ... Chamber, 9 ... AgTe alloy target, 13 ... PC
Substrate, 14 ... AgTe-C film.

Front page continuation (72) Inventor Hiroyuki Higashino 70 Yanagimachi, Saiwai-ku, Kawasaki City, Kanagawa Stock Company, Toshiba Yanagimachi Plant (56) References JP-A-1-199333 (JP, A) JP-A-2-112984 ( JP, A) JP 1-158633 (JP, A) JP 1-169747 (JP, A) JP 60-179953 (JP, A)

Claims (2)

(57) [Claims] 1. A substrate, and an Ag-Te alloy and an amorphous recording layer containing carbon and hydrogen, which is formed on the substrate and records information by irradiation with laser light. Characteristic information recording medium. 2. A substrate, an Ag-Te alloy and a carbon which are formed on this substrate and whose information is recorded by irradiation of a laser beam and whose Ag content is in the range of 2 atom% to 55 atom%. An information recording medium comprising: an amorphous recording layer containing hydrogen.