JPH01287840A - Information recording medium - Google Patents

Abstract

PURPOSE:To execute initial crystallization and information erasing at a high speed and to stabilize information recording by incorporating an alloy consisting of a specific compd. and N into a recording layer. CONSTITUTION:The alloy consisting of the formula InxSb100-x (x is, by atomic%, 48<=x<=52) and N is incorporated into the recording layer which causes a revers ible phase transition between two different crystal phases in the irradiated part when subjected to irradiation of a light beam. Namely, the signal level of the recorded part increases and the crystallization temp. increases while the advantage of a high crystallization rate is maintained if the N is incorpo rated into the recording layer. The reproduction signal is thereby increased while the high crystallization rate is maintained. The stable recoding of the information and the high-speed erasing thereof are enabled.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical disc in which information is recorded and erased by causing a phase change in a recording layer by irradiating a light beam such as a laser beam. Regarding information recording media such as.

(Prior art and its problems) Conventionally, so-called erasable optical disks, which allow information to be erased, have been used as large-capacity backup memories, etc., in place of computer hard disks, taking advantage of the fact that information can be rewritten. Applications are considered and are currently under development. Phase change type optical discs are attracting attention as such erasable optical discs. In this phase-change optical disk, information is stored by irradiating the recording layer with laser beams under two different conditions, which causes the portion of the recording layer to undergo a reversible phase change between two different structural states. Erase records.

Examples of materials for forming the phase change recording layer include T.
e, Ge, TeGe, InSe.

Semiconductor semiconductor compounds or metal compounds such as 5bSe and 5bTe are known, and these can take two stable states, a crystalline state and an amorphous state, and in each state, Nm
Since the complex refractive index represented by n-1k is different, the two states can be distinguished and information can be read based on the difference in reflectance or transmittance, for example. The idea of creating an optical memory by reversibly changing these two states, crystalline and amorphous, by heat treatment with a laser beam was developed by S., R. Ovshinsky.
et al., Metallurgical Tran
sactions 2 641 (1971). However, in the case of this method, the phase change between crystal and amorphous is basically used, and since the recording area is usually amorphous, which is more unstable than crystal, the recording area is There is a problem in that when left at a high temperature for a long period of time, the amorphous recorded portion returns to crystalline form, resulting in low stability of the recorded information.

On the other hand, unlike the above-mentioned methods, there is also a method in which information is recorded and erased by reversibly changing the phase between two different crystals depending on the laser beam irradiation conditions. In-8b alloy is a material that undergoes such a phase change; it becomes fine crystal grains when irradiated with a relatively long pulse width and low power laser beam, and it also becomes fine crystal grains when irradiated with a relatively short pulse width and high power laser beam. By irradiating the beam, fine crystal grains grow into relatively large crystals in a short period of time. Since these two crystals also have different complex refractive indices, information can be recorded and erased in the same way as in an optical disk that utilizes a phase change between crystal and amorphous.

A detailed examination of the recorded and erased parts of this In-5b recording layer using a transmission electron microscope (TEM) revealed that the recorded parts were In5°sb, intermetallic compound microcrystals, and sb.
It consists of coarse crystals, and the erased part is In5.
It has been found that it consists of fine crystals of ゜5bso intermetallic compound and fine crystals of sb. Therefore, In-8
b For recording and erasing of the recording layer, In5oSbs.

Segregation of excess sb from the intermetallic compound composition plays an important role. That is, when forming a recording layer using an In-3b alloy, it is necessary to use a composition containing sb in excess of In.

In fact, according to the inventor's experiments, the composition of the recording layer was changed to In.
z S b ,. . It has been confirmed that when X is set to 1 and X is set to 50 or more, that is, when the In5oSb5o intermetallic compound composition or the composition containing excessive In is used, information cannot be recorded.

However, in the composition where sb is excessive in the In-3b alloy, that is, in Inm S bloo-x, X is 5
With a composition of 0 or more, information can be recorded as described above and the reproduced signal is large, but in practical use, the initial crystallization rate and erasing rate of the recording layer, which is in an amorphous state immediately after film formation, are low. There are drawbacks. For example, In43Sbs7
When attempting to initialize crystallization by irradiating a continuous laser beam while rotating an optical disk on which a recording layer has been formed, if the disk rotation speed is as slow as 100 to 150 rpm, a laser with a power of about 6 mW is used. Crystallization is achieved by irradiating one track with a beam during one or two rotations of the disk, but the practical range is 900 to 1.
At 000 rpm, even a laser beam with a large power of 10 mW will not crystallize unless it is irradiated onto one track for 6 to 8 rotations.

The same goes for erasing, and the disk rotation speed is 30.
Orpm or less, the information can be erased by irradiating the disk with a low-power laser beam of about 6 mW for one rotation, but if the disk rotation speed is 1000 rp.
If it exceeds Im, there is a problem in that even if a 10 mW laser beam is irradiated onto a track including a recorded portion during two or three revolutions of the disk, unerased areas will remain.

On the other hand, since the aforementioned In5oSb5゜ is an intermetallic compound, the ordering (regularization) of short distances between atoms is extremely fast due to laser beam irradiation, so crystallization is extremely fast. , in this case s
Since segregation of b does not occur, information cannot be recorded. In addition, in a composition extremely close to this intermetallic compound, although the crystallization rate is relatively high, the reproduction signal is extremely small because of the slight segregation of sb, which is not practical.

This invention was made in view of such circumstances, and
An object of the present invention is to provide an information recording medium such as an optical disk that can speed up initial crystallization and erase information, and can stably record information.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention has a substrate and an irradiated portion that undergoes a reversible phase change between two different crystal phases depending on the irradiation conditions of the light beam. an information recording medium having a recording layer, the recording layer containing an alloy consisting of In, Sb+oo-x (X is atomic % and falls within the range of 48≦x≦52), and N. It is characterized by

(Function) In I n l S b too-x, X is 48≦
If x≦52, the crystallization rate is relatively high. By including N in this composition, the signal level of the recorded portion can be increased while maintaining the advantage of a high crystallization rate. Therefore, initialization and erasing characteristics are extremely good. Furthermore, since the crystallization temperature is increased by including N, the stability of the recording layer itself is extremely high, and the recorded information is also stably retained.

(Example) Examples of the present invention will be described in detail below.

In 1nxsb+oo-m, if X is in the range of 48≦x≦52, the composition ratio of In and sb deviates by only ±22 atoms from the In50 S b 50 intermetallic compound, which has a high crystallization rate, so the crystallization rate will decrease. Relatively large. However, as mentioned above, if In is 50 atomic % or more in this range, sb segregation will not occur and it will not be possible to record substantially, and even if In is less than 50 atomic %, sb The amount of segregation is too small to obtain a sufficient signal. However, according to the inventor's experiments, by adding N to an In-Sb alloy having such a composition range, it is possible to increase the signal level of the recording portion without impairing the high crystallization speed. It turned out that it can be done. Furthermore, since the crystallization temperature is increased by including N, the stability of the recording layer itself can be increased, and the recorded information is stable. In this way, I nx
By applying an alloy consisting of S b+oo-x (48≦x≦52) and N to the recording layer, extremely good characteristics can be obtained.

An alloy having this composition undergoes a phase change between a crystal in an equilibrium phase and a crystal in a non-equilibrium phase depending on the irradiation conditions of the light beam. For example 48
≦x50, I n 508 b 50 is irradiated with a relatively long pulse width and low output laser beam.
It becomes an equilibrium phase consisting of fine crystal grains of SbN and fine crystal grains of SbN, and becomes a non-equilibrium phase in which the fine crystal grains of SbN become coarse due to irradiation with a high-output laser beam with a relatively short pulse width. Note that the presence of N in the recording layer can be confirmed by Auger electron spectroscopy or the like.

According to the experiments of the inventor of the present application, InSb in the above-mentioned composition range
It has been found that the recording layer containing the alloy and N can be suitably created by sputtering using a mixed gas of A gas and N2 gas and targeting In and sb.

The information recording medium according to this embodiment is configured as shown in FIG. 1, for example. The disk-shaped substrate 11 is made of a material that is transparent and has little change over time, such as glass or polycarbonate resin, and has a pre-group formed therein. On this substrate 11, a protective layer 12, a recording layer 13, a protective layer 14, and a surface protective layer 15 are formed in this order. The protective layers 12 and 14 have the function of preventing holes from being formed due to evaporation of the irradiated portion of the recording layer 13 when the recording layer 13 is irradiated with a laser beam, and are usually made of thermally stable material. It is made of dielectric material such as 5i02. The surface protection layer 15 is made of, for example, an ultraviolet curing resin, and has the function of preventing scratches during handling.

The recording layer 13 is Inn 5tzoo, (48≦x≦52)
The irradiated portion changes phase between an equilibrium phase crystal and a non-equilibrium phase crystal depending on the laser beam irradiation conditions, and information is recorded and erased.

Next, a method for manufacturing the information recording medium configured as described above will be explained in detail with reference to FIG.

FIG. 2 is a schematic diagram showing a reactive sputtering apparatus. In the figure, 20 indicates a reaction vessel, and a gas inlet 21 and an exhaust port 22 are provided in the peripheral wall of the reaction vessel 20. A cryopump (not shown) is connected to the exhaust port 22 via a valve 24, and the inside of the reaction vessel 20 is evacuated by the cryopump when the valve 24 is open. An Ar gas supply device and a N2 gas supply device (not shown) are connected to the gas inlet 21 via a valve 23, and the Ar gas and N2 gas react through the gas inlet 21 while their flow rates are adjusted by the valve 23. It is introduced into the container 20. At the upper part of the reaction vessel 21, a disk-shaped rotating base 25 for supporting a substrate is rotatably arranged with its surface horizontal, and the substrate 11 is supported on the lower surface of this base 25. It looks like this. Further, inside the reaction vessel 20, flat electrodes 26, 27, 28 are arranged below the base 25 and facing the base 25.
RF (radio frequency) power sources (not shown) are connected to 27 and 28, respectively. Electrode 26.27.28
Above are 5i02 target 29 and In target 3 respectively.
0 and sb starters 31 are installed. Moreover, between the target 29, 30, 31 and the rotating base 25,
Shutters 32, 33, and 34 are provided, respectively.

In such an apparatus, first, the inside of the reaction vessel 20 is evacuated to, for example, 10-6 Torr using a cryopump. Next, the valve 23 is opened to introduce only Ar gas into the reaction vessel 20 at a predetermined flow rate to bring the pressure inside the reaction vessel to a predetermined value. Then, while the substrate 11 placed on the base 25 is rotated at a constant speed, only the shutter 32 is opened, and RF power of a predetermined power is supplied to the 5i02 target 29 via the electrode 26 for sputtering. A protective layer 12 of a predetermined thickness is formed on. Next, valve 2
3 to introduce N2 gas into the reaction vessel 20 at a predetermined flow rate, close the shutter 32, open the shutter 33.34, and inject the In target 30 and the SB target 31 through the electrodes 27.28, respectively. A recording layer 13 made of InSb and N is formed by sputtering by supplying an RF tB force of a predetermined power. In this case, the flow rate of N2 gas and A
If the ratio to the flow rate of r gas is N2/Ar, then OxN2/
It is preferable that Ar≦0.5. Particularly preferable characteristics can be obtained within this range. After that, the valve 23 is adjusted to stop the supply of N2 gas, and the shutter 33.34 is closed.
5i02 target 29 under the same conditions as when forming the protective layer 12 by closing the shutter 32 and opening the shutter 32 again.
Power is supplied to form the protective layer 14.

The information recording medium on which the protective layer 14 has been formed is removed from the sputtering device, and an ultraviolet curable resin is applied onto the protective layer 14 using a spinner (not shown), which is then cured by irradiating ultraviolet rays to form the protective layer 15. form.

Next, the information processing operation of such an information recording medium will be explained.

Since the initialization recording layer 13 is amorphous immediately after film formation, the recording layer 13
The recording layer 13 is continuously irradiated with a relatively weak output laser beam to melt and slowly cool the recording layer 13, changing it into an equilibrium phase crystal.

The recording information recording medium is rotated at high speed, and a laser beam pulse 18 having a higher output and a relatively shorter pulse width than that during initialization is irradiated to form a recording mark 19 in an unbalanced phase.

Irradiating the reproduction recording layer 13 with a relatively weak output laser beam,
Information is read by detecting the intensity of the reflected light from the recording layer 13.

The recording mark 19 is crystallized and the information is erased by continuous irradiation with a laser beam similar to that used in the erase initialization.

Next, a test example in which the information recording medium (optical disc) according to this example was manufactured and its characteristics were evaluated will be described.

Test Example 1 A disc-shaped polycarbonate transparent substrate was placed inside the reaction vessel of the sputtering apparatus shown in Fig. 2, and the interior of the vessel was heated for 10 minutes.
After exhausting the air to -6T orr, put the gas A into the container.
The flow rate of O5CCM was introduced, and the gas pressure was 6 m Torr.
I made it r. 5i02 with the shutter closed in this state
400W at 13.56MHz via electrode to target
Bliss sputtering is performed by applying RF power for about 2 minutes.
Thereafter, the shutter was opened and sputtering was performed for 5 minutes to deposit 1000 5i02 protective layers on the substrate. Next, the mixing ratio of Ar gas and N2 gas was set to 1/10, the gas pressure in the reaction vessel was set to 5 m Torr, the electrodes were opened, and 95 W was applied to the In target and the SB target, respectively. RF7rS force of about 2 with the shutter closed
After applying it for 1 minute and performing bliss sputtering, the shutter was opened and sputtering was performed for 2 minutes and 30 seconds in a plasma of a mixed gas of Ar gas and N2 gas.
A recording layer made of In4sSbs2 and N was formed. After that, the supply of N2 gas was stopped and the 5i0
A 5i02 protective layer was again formed on the recording layer by 1000 people under the same conditions as the 2nd protective layer. Then, apply ultraviolet curing resin on the outer 5i02 protective layer using a spinner,
The resin is cured by irradiating ultraviolet light at mW for about 1 minute, and the resin is cured for about 1 minute.
A surface protective layer of 0 μm was formed, and a disk sample was prepared. This disc was designated as sample D.

Flow rate ratio N of N2 gas and Ar gas when forming the recording layer
2/Ar respectively 0.0.01.0.05.0.2.0.
Samples ASBSC, E, and F were prepared under the same conditions as sample D except that they were changed by 5 and 1.0, respectively.
It was designated as SG.

The characteristics of these samples were evaluated using a performance evaluation device.

Note that the disk rotation speed was set at a high speed of 120 Orpm. The evaluation procedure is shown below.

(a) Immediately after the film is formed, the amorphous recording layer is irradiated with a continuous laser beam of 7 mW to transform it into a crystal in an equilibrium phase. If complete crystallization was not achieved in one rotation, the same portion was irradiated until crystallization was completed.

(b) The output is 12 mW in the initially crystallized track part,
A laser beam with a pulse width of 100 nsec and a duty ratio of 50% was irradiated to form a recording mark made of non-equilibrium crystal.

(C) A continuous laser beam of 0.5 mW was irradiated onto the track on which the recording mark was formed, a reproduced signal from the recording mark was read out, and the amplitude of this signal was measured.

(d) The recording layer was irradiated with continuous light of 7 mW in the same manner as in the initial crystallization to change the recording mark of the non-equilibrium layer crystal again to the equilibrium layer crystal, thereby erasing the information. In addition, during initial crystallization, light light was continuously irradiated many times until crystallization, but during erasing, light was irradiated continuously for only one revolution, and when the crystal did not completely return to the equilibrium layer crystal. , (c), a reproduction light of 0.5 mW was irradiated, and the magnitude of the signal amplitude was measured as an erased residue.

The number of laser irradiations for initial crystallization measured in this way,
Table 1 shows the values of the signal amplitude of the recorded portion and the amplitude of the erased remaining signal.

Table 1 In Table 1, the number of laser irradiations for initial crystallization indicates the number of rotations of the disk required to crystallize one track. According to this Table 1, the number of rotations of the disk is 12
Even at 0.00 rpm, by adding N, In
The recording signal increases without impairing high-speed crystallization, which is an advantage of the 50Sb5° composition, and N2/Ar is 0.05 and 0.1.
In samples C and D, the amplitude of the recording signal was the largest at 100, and there was no signal remaining after erasure. On the other hand, sample G with N2/Ar of 1.0 had a low crystallization rate and was unable to record information.

Test Example 2 Using an apparatus similar to the sputtering apparatus used in Test Example 1, the RF power input to the In target and the SB target was changed to adjust the base composition of the recording layer to 1n45s, respectively.
bss, In5oSb, 6°In52Sb4a
, Sample D (N2/A-0,0
Four disk samples were prepared under the same conditions as in 5),
Samples H and I, respectively.

J, Nitoshi. Regarding sample H, the signal amplitude of the recorded portion was extremely large at 200 mW, but the sb was too excessive and there was a large amount of unerased data.

In addition, for sample K, In was too excessive and N
It was not possible to obtain a sufficient signal even after adding . On the other hand, Samples I and J were able to obtain the same good results as Sample D.

Test Example 3 Seven samples in which 3,000 thin films of In4BSb52 and N were formed on a small piece of glass substrate by sputtering in the same manner as in Test Example 1, changing N2/Ar in 7 steps. was created. The crystallization temperature of these samples was measured using a differential scanning thermal analyzer (DSC).
It was measured by The results are shown in FIG. FIG. 1 is a graph showing the relationship between N2/Ar on the horizontal axis and crystallization temperature on the vertical axis. From this figure, it can be seen that as the amount of N added increases, the crystallization temperature increases rapidly. From this, sample F,
The increase in the number of initial crystallizations and the occurrence of erased residues in G are considered to be due to the crystallization temperature being too high. However, if N2/Ar is 0.5 or less, not only good initialization characteristics and erasing characteristics are maintained as shown in Test Example 1, but also the crystallization temperature is lower than that of the case without N. Since this is high, it can be expected that the thermal stability of the recording layer itself and the storage stability of the recorded marks will be good.

[Effect of the invention] According to this invention, In, Sb+oo-x (48≦
x≦52) and a recording layer containing N,
-3b While maintaining a high crystallization rate of the gold metal compound,
The reproduction signal can be increased and information can be stably recorded. Therefore, high-speed erasing is possible, and recording and erasing are possible even when the disk is rotated at high speed. That is, according to the present invention, it is possible to obtain an information recording medium having a recording layer having extremely good characteristics as an erasable type.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing a sputtering apparatus used for manufacturing an information recording medium according to an embodiment of the present invention, and FIG. is N2 gas and Ar during recording layer formation.
FIG. 3 is a graph showing the relationship between gas ratio and crystallization temperature of a recording layer. 11; Substrate, 12, 14, 15; Protective layer, 13; Recording layer, 18; Laser beam, 19; Recording mark. Applicant's agent Patent attorney Takehiko Suzue i'f--18 1 to 1 Figure 2

Claims (1)

[Claims] An information recording medium comprising a substrate and a recording layer whose irradiated portion reversibly changes phase between two different crystal phases depending on the irradiation conditions of a light beam, the recording layer being In_xSb.
_1_0_0_-_x (x is atomic%, 48≦x≦
It is within the range of 52. ) and N.