JPH01286128A - Information recording medium - Google Patents

Abstract

PURPOSE:To enable fast erasing and to contrive to record and erase in fast rotation by constituting a recording layer of TeAuN alloy having a specific composition. CONSTITUTION:A protective layer 12, recording layer 13, protective layer 14 and surface protective layer 15 are formed on a substrate 11 on which pregrooves are already provided. The recording layer 13 is constituted of Te100-xAux(x represents atomic%, 1<=x<=8) alloy to which N is added. As the crystallization rate of Te is high, a recording mark 19 in the recording layer 13 can be crystallized and erased fast by continuous irradiating with laser beam 18. Thus, recording and erasing can be performed even when the disk rotates fast, as well as the amorphous recording mark can be stabilized owing to rather high temp. of crystallization.

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. Such erasable type optical disks include a magneto-optical type in which information is recorded and erased by controlling the spin direction of a perpendicular magnetization film, and a phase change type. Among these, the phase change method is attracting attention because, unlike the magneto-optical method, it is possible to record, reproduce, and erase by controlling only the irradiation conditions of the light beam, and it also has the possibility of an overwrite method using a single laser beam. ing. This phase change type optical disc uses a phase change type recording layer in which the beam irradiation area changes reversibly between, for example, a crystalline phase and an amorphous phase by changing the conditions of the irradiated laser beam. Record and delete information. In this case, since the complex refractive index expressed by N-n-1k is different in each state, it is possible to read information by distinguishing between the two states, for example, based on the difference in reflectance or transmittance (S, R, 0v
Shinsky MetalurglcalTran
sactions 2 841 1971)
.

Examples of such phase-change materials include GeTe.
, In5eSSbSe, 5bTe, etc. are known, and are usually made amorphous by irradiating the crystal with a light beam under certain conditions to form information recording portions (hereinafter referred to as recording marks).

Among these, GeTe can obtain good recording and erasing characteristics as a phase change recording layer, but has the disadvantage that it has low oxidation resistance and its reflectance etc. quickly decrease in high temperature and humid environments. has.

Also, relatively good recording and erasing characteristics can be obtained when the recording layer is formed with 5bSe, 5bTe, but recording layers made of these materials cannot meet the recent demands for higher recording densities. This method has the disadvantage that it cannot cope with the accompanying high-speed rotation of the disk. That is, these materials have a low crystallization rate and therefore a low erasing rate; for example,
If the disk is rotated at a high speed of 180 rpm, unerased portions will remain.

In contrast, attempts have been made to avoid the above-mentioned drawbacks by forming a recording layer by adding, for example, Te and Co to InSe, which has such drawbacks. That is,
The recording layer made of In5eTeCo makes the disc 180O
The recording and erasing characteristics are good even when rotated at a high speed of rpm, and since the crystallization temperature is as high as 300° C. or higher, the stability of the amorphous recording mark is high. However, this I
n5eTeCo generates 25mW at the recording surface during recording.
There is a disadvantage that it is necessary to irradiate a high-power light beam. In other words, this 25 mW is the value after passing through the optical system such as the objective lens, and the laser oscillation source requires an output of approximately 50 mW, but semiconductor lasers with such high output are not currently commercially available. First, it is necessary to specially manufacture such a semiconductor laser, and currently experiments are being conducted using semiconductor lasers that have been prototyped for research purposes.

This invention was made in view of the above circumstances, and even when the disk is rotated at high speed, information can be recorded and erased using a light beam with relatively low irradiation output.
It is an object of the present invention to provide an information recording medium having a recording layer in which recording marks are stably present and having high environmental resistance.

[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 reversible between two phases in which the atomic arrangement is different from each other depending on the irradiation conditions of the light beam. an information recording medium having a recording layer that undergoes a phase change, the recording layer having a phase change of T e +oo
-x A u x (X indicates atomic%, 1≦x≦8
It is characterized by being made of an alloy in which N is added to

(Function) Since the alloy with the above composition contains Te, which has a high crystallization rate, by forming the recording layer with this alloy, high-speed erasing becomes possible, and recording and erasing are possible even when the disk is rotated at high speed. It is possible. Furthermore, since this alloy has a relatively high crystallization temperature, amorphous recording marks are stable.

Furthermore, since this alloy itself is difficult to oxidize, it has high environmental resistance. Furthermore, this alloy can be recorded and erased by a light beam with relatively low illumination power.

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

As a result of various studies on the alloy composition of the recording layer, the inventor of the present application found that a recording layer made of a ternary alloy in which N is contained in Te+oo-x Aux (1≦x≦8) has extremely good characteristics.

The reason why such a TeAuN alloy exhibits good characteristics as a recording layer will be explained below. Since Te is a chalcogenide-based element, it easily becomes amorphous, but since the crystallization temperature is as low as 15°C, amorphous recording marks formed by irradiation with a light beam such as a laser beam can be instantly destroyed. It returns to crystal. Further, although Te has a relatively high crystallization speed, the crystallization speed is still insufficient considering the erasing speed required in recent years. On the other hand, when 1 to 8 at. can be converted into According to experiments by the inventor of the present application, when the recording layer was formed of such a TeAu alloy, recording and erasing was possible up to a rotational speed of 1200 rpm on a disc-shaped information recording medium. In this TeAu alloy, A
When the amount of u is less than 1 atomic %, the characteristics are almost the same as those of Te alone, and when it exceeds 8 atomic %, Au atoms aggregate during laser beam irradiation, resulting in phase change characteristics corresponding to recording/erasing. decreases. Therefore, Te roo-
It is preferable that x A u X is in the range of 1≦x≦8. This T e too-X A u X
(1≦x≦8), the crystallization temperature is relatively low, so the stability of amorphous recording marks is low. However, the crystallization temperature of TeAuN ternary alloy made by adding N to this alloy is about 320 to 33
The temperature is extremely high, reaching 0°C, and the stability of recorded marks is also dramatically improved. Moreover, this ternary alloy not only has a high crystal temperature, but also allows recording and erasing under high speed rotation even when the irradiation output of the light beam is low. That is, TeAu alloy can only record and erase up to 120 rpm, whereas TeAuN alloy in the above range can record and erase up to 1800 rpm.
Recording and erasing is possible even at high speed rotations of m.

This TeAuN alloy can be produced by sputtering using a TeAu alloy target or by dual simultaneous sputtering using a Te target and an Au target in a mixed atmosphere of A gas and N2 gas.

In the TeAuN alloy film prepared in this way, N cannot be quantitatively determined by ICP analysis or fluorescent X-ray analysis because N has a small atomic weight and usually exists in gaseous form. However, the presence of N can be qualitatively determined by Auger spectroscopy. can be confirmed.

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 made of Te, as described above. . -1A u X
It is formed of an alloy in which N is added to (l≦x≦8), and the irradiated portion changes phase between a crystalline phase and an amorphous phase depending on the laser beam irradiation conditions.

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 this reaction vessel 21. A cryopump (not shown) is connected to the exhaust port 22 via a valve 24, and the inside of the reaction vessel 20 is exhausted by this cryopump when the valve 24 is open. A (not shown) is connected to the gas inlet 21 via a valve 23.
The r gas supply device and the N2 gas supply device are connected, and the A gas and N2 gas are introduced into the reaction vessel 20 through the gas inlet 21 while the flow rate is adjusted by the valve 23. A disk-shaped rotary base 25 for supporting the substrate is rotatably arranged with its surface horizontally on the top of the base 25, and the substrate 11 is supported on the lower surface of this base 25. Further, within the reaction vessel 20, plate-shaped electrodes 26 and 27 are arranged below the base 25 so as to face the base 25, and each of the electrodes 26 and 27 has an RF ( A 5i02 target 28 and a TeAu alloy target 2 of a predetermined composition are connected on the electrodes 26 and 27, respectively.
9 has been installed. Furthermore, shutters 30 and 31 are provided between the targets 28 and 29 and the rotating base 25, respectively.

In such an apparatus, first, the inside of the reaction vessel 20 is evacuated to, for example, 10 Torr using a cryo bomb. Next, the valve 23 is opened and only the A gas is introduced into the reaction vessel 20 at a predetermined flow rate to bring the pressure inside the reaction vessel to a predetermined value.Then, the substrate 11 installed on the base 25 is rotated at a constant speed. 5i by opening only the shutter 30 while
02 target 28 is supplied with RF power of a predetermined power from the power supply 32 via the electrode 26 to perform sputtering, thereby forming the protective layer 12 of a predetermined thickness on the lower surface of the substrate 11. next,
N2 gas is also introduced into the reaction vessel 20 at a predetermined flow rate by adjusting the valve 23, the shutter 30 is closed, the shutter 31 is opened, and RF power of a predetermined power is supplied to the TeAu target 29 from the power source 33 via the electrode 27. Then, sputtering is performed to form a recording layer 13 made of Te and N. Thereafter, the valve 23 is adjusted to stop the supply of N2 gas, the shutter 31 is closed, and the shutter 30 is opened again to supply RF power to the 5i02 target 28 under the same conditions as when forming the protective layer 12. A protective layer 14 is formed.

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.

Note that when an information recording medium is produced in this way,
As mentioned above, the recording layer exhibits good recording/erasing characteristics even when rotated at high speed and has excellent environmental resistance, but has a short repeated recording and erasing life.

That is, in the case of the erasable method, it is preferable that recording and erasing can be repeated about 104 times, more preferably 106 times, but in the case of the above-mentioned method, the number of times recording and erasing can be repeated is about 104.
After repeated recording and erasing, recording becomes difficult.

The following reasons can be considered for the short cycle life. That is, Te formed by the method described above
In the AuN recording layer, N enters in an extremely weakly bonded state, so by repeatedly irradiating the laser beam, the irradiated area experiences a temperature cycle between several hundred degrees Celsius and room temperature, and during that time, N gradually Atoms are ejected from the recording layer.

In other words, when forming a film by sputtering in a normal Ar gas atmosphere, RF power is applied to a flat electrode placed directly above the target, so the intensity of plasma emitted by Ar+ ions is extremely high directly above the target. While there is a region where the plasma is strong, such plasma light emission does not reach the vicinity of the substrate that is slightly layered from that region, but normally the target atoms activated by the collision of the A"+ ions. Alternatively, the compound collides with the substrate with a predetermined kinetic energy and adheres to it. However, in sputtering using a mixed gas of N2 gas and Ar gas, N2 gas is a very stable gas, so N is It is thought that the N2 gas is in an activated excited state only in the area where the plasma emission intensity directly above the target is high, and that it is a neutral and stable N2 gas near the substrate.

Therefore, it is thought that in the TeAuN recording layer sputtered by simply introducing a mixed gas as described above, N exists in a weakly bonded state, or N simply physically invades while remaining neutral and stable. It will be done.

For this reason, in order to extend the repeated recording and erasing life, it is necessary to
It is thought that it would be sufficient if it could be brought into an excited state. FIG. 3 is a schematic configuration diagram showing a sputtering apparatus capable of exciting N in the vicinity of a substrate, and FIG. 4 is a sectional view taken along the line IV--IV. In FIG. 3, the same parts as in FIG. 2 are given the same reference numerals, and their explanation will be omitted. In this device, unlike the device in Fig. 2,
A discharge electrode 41 is provided directly under the base 25, and an RF power source 42 is connected to this electrode 41.
Electricity is supplied to the electrode 41 from. This electrode 41 has a ring shape as shown in FIG. 4, and is connected to a gas introduction pipe 43 through which N2 gas is introduced from a gas supply device (not shown) through a valve 45. Further, a gas discharge hole 44 is formed in this electrode 41 to discharge N2 gas toward the inside thereof. An Ar gas inlet 51 is provided below the gas inlet vibe 43 on the side wall of the reaction vessel 20, and a valve 52 is connected to an Ar gas supply device (not shown).
Ar gas is introduced through.

When forming a TeAuN recording layer using such an apparatus, first, a predetermined RF power is applied to the electrode 41 from the power source 42, and while adjusting the flow rate with the valve 45, the electrode 41 is heated through the gas introduction pipe 43. Introduce N2 gas. This excites the N2 gas and releases it from the hole 44, forming a plasma 46. At this time, the gas inlet 51
A predetermined flow rate of Ar gas is introduced from
and sputtering. In this case, since N is in an excited state near the substrate 11, N and TeAu
It can strengthen the bond with the alloy.

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

Since the initialization recording layer 13 is amorphous immediately after being formed, the recording layer 13 is continuously irradiated with a relatively weak output laser beam while rotating the optical disc at a low speed to melt and gradually cool the recording layer 13. crystallize.

The recording information recording medium is rotated at high speed and a high-power laser beam pulse 18 is irradiated to form an amorphous recording mark 19.

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 installed in the reaction container of the sputtering apparatus shown in Fig. 2, and the inside of the container was heated to 10
After evacuation to −6 Torr, Ar gas was introduced into the container at a flow rate of IOSCCM while rotating the substrate at 5 Q rpm, and the gas pressure was set to 5 m Torr. In this state, with the shutter closed, apply 400 W of RF power at 13.56 MHz to the 5i02 target for about 2 minutes through the electrode to perform bliss sputtering, then open the shutter and apply 400 W of RF power for about 10 minutes. A 5LO2 protective layer of 1000 layers was deposited on the substrate. Then, N2
Gas gas was introduced into the ISCCM, the mixing ratio of Ar gas and N2 gas was set to 1/10, and the gas pressure in the reaction vessel was set at 5 mT.
orr, and applied 600W RF'1 power to the Teg5Au5 target for about 3 minutes through an electrode, and sputtered a mixed gas of Ar gas and N2 gas in the plasma onto the protective layer. 1000 T e
A recording layer of an alloy having a composition of A u 5 containing N was formed. After that, the supply of N2 gas was stopped, and the above-mentioned 5i
A 5i02 protective layer was again formed on the recording layer by 1000 people under the same conditions as the 02 protective layer. Then, after removing the disk from the sputtering device, UV curable resin was applied onto the outer 5i02 protective layer using a spinner, and 250 mW
The resin is cured by irradiating it with ultraviolet rays for about 1 minute, and the thickness is about 10μ.
A surface protective layer of m was formed, and a disk sample was prepared.

Next, this sample was tested using a performance evaluation device according to the procedure shown below.

(a) While rotating the disk sample at 30 rpm, the recording layer of the disk sample was irradiated with a continuous laser beam of 10 mW for initial crystallization.

(b) Disk sample w While rotating at 1800 rpm, output 15 m to the track part where initial crystallization occurred.
Amorphous recording marks were formed by irradiation with a laser beam of W, pulse width of 100 nsec, and duty ratio of 50%.

(C) A continuous laser beam of 0.8 mW was irradiated onto the track on which the recording mark was formed, a signal from the recording mark was reproduced, and the magnitude of this signal was measured.

(d) While the rotational speed of the disk sample was kept at 180° rpm, the recording layer was irradiated with continuous light of 10 mW to recrystallize the recording marks and erase the information.

(e) Irradiate the erased area with 0.8 mW continuous light and measure the signal size of the amorphous recording mark? #1 was established.

As a result, a reproduced signal of the recording mark with an AC signal amplitude of about 100 mV was obtained, and the AC signal of the reproduced signal of the erased portion was OmV, and there was no remaining signal.

This disk sample was left in an environment with a temperature of 70° C. and a humidity of 90% RH and changes in reflectance were measured. As a result, the reflectance hardly changed even after 4 weeks.

Note that the gas flow rate ratio is kept constant, and only the composition of the alloy target is changed from T e ggA u 1 to T e g2A u
As a result of preparing multiple samples made by changing Au by 1 atomic % up to B and conducting similar tests, 5 results were obtained.
Good results were obtained, similar to the sample described above using the T e 95A u 5 target.

Test Example 2 In this test example, a disk sample was produced using the sputtering apparatus shown in FIG. A polycarbonate substrate similar to that in Test Example 1 was placed in a reaction vessel, and a 5i02 protective layer of 100% was coated on the substrate under the same conditions as in Test Example 1.
It was formed with a thickness of 0. Next, A "Gas 1105C
C was maintained, and N2 gas was supplied to the gas discharge electrode at a flow rate of ISCCM. That is, the flow rate ratio N 2 /A r was set to 1/10. Then, the mixed gas pressure in the reaction vessel was set to 5 m Torr, and with the shutter closed, approximately 60 W of RF power was supplied from the power source to the T e , Au 5 alloy target via the electrode, and the alloy Plasma was emitted onto the target. At the same time, RF power of 200 W was supplied from the power supply to the gas discharge electrode to cause plasma generated by N2 gas to be emitted near the gas discharge electrode, that is, near the substrate. After performing bliss sputtering for 2 minutes in this manner, the shutter was opened and sputtering was performed for about 7 minutes, and T e , 6. A recording layer of an alloy containing Au 5 and N was formed to a thickness of 1000 mm. Thereafter, the supply of N2 gas was stopped, and an outer protective layer of 1000 people was formed under the same conditions as Test Example 1, and a surface protective layer of about 10 μm was formed thereon to prepare a disk sample.

This disk sample was tested using the same performance evaluation device as Test Example 1, and the same results as Test Example 1 were obtained. Further, as a result of conducting the same environmental resistance test as in Test Example 1, the reflectance hardly changed even after 4 weeks as in Test Example 1.

Next, using this disk sample, recording and erasing were repeated under the above conditions. Each time, the reproduced signal (amplitude of the AC signal) of the recording mark and the signal remaining after erasing were fixed at n1 using a continuous laser beam of 0.8 mW. As a result, it was possible to record and erase up to about 104 times.

On the other hand, when a similar test was conducted on the disk sample prepared in Test Example 1, it became difficult to record after repeating recording and erasing approximately 100 times. As a result, it was confirmed that by using the apparatus shown in FIG. 3 in which N2 gas is excited in the vicinity of the substrate, the repeated recording and erasing life can be significantly improved.

Note that the gas flow rate ratio was kept constant, and only the composition of the alloy target was changed from T e 99A u 1 to T e 92A u
As a result of preparing multiple samples made by changing Au by 1 atomic % between T and B and conducting similar tests, T
Good results were obtained similar to the above sample using the e*5Au5 target.

In the above embodiments, the recording layer was formed by sputtering, but the recording layer is not limited to this, and may be formed by other methods such as heating vapor deposition of a TeAu alloy ingot or heating co-evaporation of a Te ingot and an Au ingot.

Further, although the N2 gas was excited with AC power from an RF power source, the same results can be obtained using DC power.

[Effects of the Invention] According to the present invention, since the recording layer contains Te, which has a high crystallization speed, by forming the recording layer with this alloy, high-speed erasing is possible, and recording is possible even when rotating at high speed. and can be erased.

Furthermore, since the alloy forming the recording layer has a relatively high crystallization temperature, amorphous recording marks are stable. Furthermore, since this recording layer itself is not easily oxidized, it has high environmental resistance. Furthermore,
This recording layer can be recorded and erased by a light beam with relatively low irradiation power. That is, 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 cross-sectional view showing an information recording medium according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic configuration diagrams showing a sputtering apparatus used for manufacturing the information recording medium according to an embodiment of the present invention. , FIG. 4 is a horizontal sectional view of the sputtering apparatus of FIG. 3. 11; Substrate, 12, 14, 15; Protective layer, 13; Recording layer, 18: Laser beam, 19; Recording mark. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] An information recording medium comprising a substrate and a recording layer whose irradiated portion reversibly undergoes a phase change between two phases in which the atomic arrangement is different depending on the irradiation conditions of a light beam, the recording layer being Te_1_0_0_-. An information recording medium characterized in that it is made of an alloy in which N is added to _xAu_x (x represents atomic % and falls within the range of 1≦x≦8).