JPH07105070B2 - Information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to information for erasing information by causing a phase change in a recording layer by irradiating a light beam such as a laser beam. Recording medium

(Prior Art) Conventionally, a phase change type optical disc has been known as an erasable optical disc. In this phase change type optical disc, information is recorded / erased by irradiating the recording layer with a laser beam to reversibly change the phase of the recording layer between crystalline and amorphous. .

Examples of such phase change materials include Te, Ge, Te
There are semiconductors such as Ge, InSe, SbSe, and SbTe, semiconductor compounds, and intermetallic compounds. These selectively take two states, a crystalline phase and an amorphous phase, depending on the temperature, and in each state, the complex refractive index expressed by N = n-ik is different,
Information is recorded and erased by reversibly changing these two states by heat treatment with a laser beam (SROvshinsky Meta
llurgical Transactions 2 641 1971).

A method of recording and erasing information by this technique will be described. At the time of recording, after the recording layer is initially crystallized, the recording layer is irradiated with a high-energy laser beam, and the recording layer is melted and rapidly cooled to amorphize that portion to form a recording pit. At the time of erasing, the recording pit is irradiated with a laser beam having a relatively low energy with a relatively long pulse width, and the irradiated portion is gradually cooled to crystallize the once-amorphized recording pit.

An optical disc of the type in which information is recorded and erased by such a phase change between crystalline and amorphous has, for example, the layer structure shown in FIG. That is, a protective layer 2 made of a chemically and thermally stable dielectric material is formed on a transparent substrate 1 made of glass or an organic resin.
The recording layer 3 is formed on the recording layer 3, and the protective layer 2 is formed on the recording layer 3.
A protective layer 4 made of the same material as above is formed, and further a protective layer 5 made of an ultraviolet curable resin is formed on the protective layer 4 in order to prevent scratches caused in handling.

Among these, the protective layers 2 and 4 have the following roles.

When the recording layer 3 is irradiated with the laser beam, the recording layer 3 is prevented from being heated and evaporated to form a hole, and deformation of the recording layer 3 due to repeated recording and erasing is prevented.

It has an enhancement effect of increasing the signal at the time of reproduction by utilizing optical interference.

It functions as a temperature control layer that facilitates heat release from the recording layer 3 during laser beam irradiation and facilitates rapid amorphization.

Among them, it is preferable that the protective layer is made of a dielectric material having a relatively high thermal diffusivity in order to function as the temperature control layer. Materials that fulfill these two roles as well as the role of the temperature control layer include SiO ₂ , SiN _4, and Al ₂ O ₃ .

(Problems to be Solved by the Invention) However, in an optical disc of a type in which information is recorded and erased by changing the phase of the recording layer between a crystalline phase and an amorphous phase, the recording layer is made amorphous. Therefore, the quenching rate depends on the material forming the recording layer, and the appropriate thermal diffusivity of the protective layer depends on the material of the recording layer. Therefore, depending on the combination of these, there may be a case where an amorphous recording pit is not formed in the recording layer. For example, as the recording layer 3, Sb
In the optical disc using Te and Si ₃ N ₄ as the protective layers 2 and 4, the cooling pits do not become amorphous due to insufficient cooling with the laser beam with high energy and short pulse width as described above. , Unable to record information. When the protective layers 2 and 4 are formed of Al ₂ O ₃ having a thermal diffusivity larger than Si ₃ N ₄ , the heat of the portion irradiated with the laser beam is
Since it was transiently emitted from 4, the portion of the SbTe beam irradiation was not melted, and as a result, information could not be recorded.

The present invention has been made in view of such circumstances,
When the recording layer irradiated with the laser beam is made amorphous and the recording pitch is formed, the recording layer can be cooled at an appropriate cooling rate, and the portion irradiated with the light beam can be made amorphous with high efficiency. It is an object of the present invention to provide an information recording medium capable of achieving the above.

[Structure of the Invention] (Means for Solving Problems) An information recording medium according to the present invention includes a substrate, a recording layer on which information is recorded and erased by being phase-changed by irradiation of a light beam, and a substrate. An information recording medium having a first protective layer formed between a recording layer and a recording layer, and a second protective layer formed on the recording layer, wherein the first protective layer and the recording layer And an interface between the recording layer and the second protective layer have an uneven portion.

(Operation) In the present invention, the interface between the first protective layer and the recording layer,
In addition, an uneven portion is formed at the interface between the recording layer and the second protective layer. When the recording layer is irradiated with a light beam and recording pits are formed in the irradiated portion, the unevenness is formed by changing the shape of the unevenness according to the combination of the material of the recording layer and the material of the protective layer. The amount of heat radiation of the protective layer can be finely adjusted so that the cooling rate of the layer is appropriate. In this case, this uneven portion can be formed by sputter etching,
The height of the uneven portion is preferably 10 to 200Å.

(Example) Hereinafter, the Example of this invention is described concretely.

An information recording medium according to this embodiment is, for example, FIG. 1 (a).
It is configured as shown in. The substrate 11 is made of a material that is transparent and does not easily change with time, such as glass or polycarbonate resin. On the substrate 11, a protective layer 12, a recording layer 13 and a protective layer 14 are formed in this order. The protective layers 12 and 14 are arranged so as to sandwich the recording layer 13, and prevent the recording layer 13 from being melted and damaged by the irradiation of the laser beam, and adjust the heat radiation amount from the recording layer 13 to prevent The cooling rate of the laser beam irradiation portion is adjusted. The protective layers 12 and 14 are made of SiO ₂ , Si ₃ N ₄ and Al ₂ O.
_It is made of a material with a relatively high thermal diffusivity such as ₃ and assists in heat dissipation from the laser beam irradiation portion of the recording layer. As a result, the light beam irradiation portion of the recording layer 13 can be rapidly cooled to be amorphized, and recording pits can be formed. The recording layer 13 is formed of, for example, an Sb-Te alloy, and this alloy changes its phase between a crystalline phase and an amorphous phase due to the difference in laser beam irradiation conditions. In addition,
As shown in FIG. 1 (b), SiO ₂ , Si ₃ N is formed on the recording layer 13.
₄ and a protective layer 15 composed of a main layer 16 formed of Al ₂ O _{3 and the} like and an auxiliary layer 17 may be formed. In this case, the recording layer
A main layer 16 is formed on 13 and an auxiliary layer 17 is formed thereon.
The auxiliary layer 17 is formed of, for example, an ultraviolet curable resin, and has a role of preventing a scratch or the like from being generated on the surface in handling the disc.

Further, the interface between the protective layer 12 and the recording layer 13 and the interface between the recording layer 13 and the protective layer 14 or the protective layer 16 are uneven,
The contact area between the recording layer 13 and each protective layer is increased to increase the amount of heat radiation from the recording layer.

An apparatus for forming such an optical disk will be described with reference to FIG. 2 by taking as an example a case where a protective layer sandwiching a recording layer is formed of Si ₃ N ₄ . Reference numeral 21 in the figure denotes a reaction vessel, and an exhaust port 31 and a gas introduction port are provided on the peripheral wall of the reaction vessel 21.
30 are provided. A cryopump (not shown) is connected to the exhaust port 31, so that the inside of the reaction vessel 21 is exhausted. An argon gas supply device (not shown) is connected to the gas inlet port 30,
Argon gas is introduced into the reaction vessel 21 via 30. Further, a flow rate adjusting valve 39 is attached to the gas inlet 30. The disk-shaped substrate 11 is supported by a rotating base 22 in the upper part of the reaction vessel 21 with its surface horizontal, and is supported by a motor (not shown).
The substrate 11 is rotated by rotating 22. In addition, plate-shaped electrodes 26, 27, 28 are arranged in the reaction vessel 21 so as to face the substrate 11, and these electrodes 26, 27, 28 are respectively provided with an RF (radio frequency) power source 3
It is connected to 5,36,37. On this electrode 26, 27, 28,
An Sb target 23, a Si ₃ N ₄ target 24, and a Te target 25 are installed respectively. Further, shutters 32, 33, 34 are arranged between the targets 23, 24, 25 and the substrate 11, respectively. Further, an RF power source 40 is connected to the rotary base 22.

In this film forming apparatus, first, the inside of the reaction vessel 21 is evacuated to a vacuum of, for example, 10 ⁻⁶ Torr by a Clion pump. Then, the valve 39 is opened to supply argon gas and nitrogen gas.
It is introduced into the reaction vessel 21 at a ratio of 1: 1 and the gas pressure in the reaction vessel is adjusted to a predetermined value. The substrate 11, for example, while rotating at 60 rpm, the electrode from the Si ₃ N ₄ RF power source 36 to the target 24 27
RF power is supplied through the protective layer of a predetermined thickness on the substrate 11.
Forming twelve. In this case, the shutter 33 is opened and the shutters 32 and 34 are closed. Then, the supply of nitrogen gas was stopped, the reaction vessel 21 was filled with argon gas only, and the valve 39
To adjust the argon gas pressure again. And RF
RF power is supplied from the power supply 39 to the rotary base 22 to sputter-etch the surface of the protective layer 12. As a result, the surface of the protective layer 12 becomes uneven.

After that, the power supply 40 is turned off, the shutter 33 is closed, the shutters 32, 34 are opened, and RF power is supplied from the power supplies 35, 37 to the targets 23, 25 via the electrodes 26, 28, for example, Sb ₆₀ Te ₄₀ A recording layer 13 having a predetermined thickness is formed on the protective layer 12.
In this case, the power supplied to the targets 23 and 25 and the recording layer 1
The relationship with the composition of 3 is already known.

Next, RF power is supplied from the RF power source 39 to the rotary base 22 again to sputter-etch the surface of the recording layer 13. Power 40
After turning off, the nitrogen gas is again introduced into the reaction vessel 21, the supply ratio of the argon gas and the nitrogen gas is set to 1: 1 to bring the inside of the reaction vessel 21 to a predetermined pressure, and the RF power supply 36 is turned on again to protect it. The protective layer 14 is formed under the same conditions as the layer 12. Protective layer 15
When forming, the main layer 16 made of Teflon is formed by the same operation, then the substrate is removed from the sputtering apparatus, the ultraviolet curing resin is applied on the main layer 16 by spin coating, Ultraviolet rays are irradiated to form the auxiliary layer 17.

Next, the operation of such an optical disc will be described.

Initialization Since the recording layer 13 is amorphous immediately after film formation, the recording layer 13 is continuously irradiated with a laser beam, and the recording layer 13 is melted and gradually cooled to be solidified to change its phase to crystalline.

Recording A short pulsed laser beam 18 on the initialized recording layer 13
Is irradiated, and the irradiated region is once melted and then rapidly cooled to change the phase to an amorphous phase to form the recording pit 19. In this case, if the thermal diffusion coefficients of the protective layers 12 and 14 are slightly small and the interface between the recording layer 13 and each protective layer is smooth, the recording layer 13
Even when it is impossible to cool the beam irradiation portion of the recording layer 13 at a sufficient cooling rate, by improving the heat dissipation of the recording layer 13 by making the interface between the recording layer 13 and each protective layer uneven. The beam-irradiated portion of the recording layer 13 can be rapidly cooled to be made amorphous. Further, by changing the shape of the unevenness, the heat radiation amount of the recording layer 13 can be adjusted,
The amount of heat radiation can be finely adjusted so that the cooling rate is optimum according to the constituent material of the recording layer 13.

Information is read by irradiating the reproducing / recording layer 13 with a relatively weak laser beam and detecting the intensity of the reflected light of the recording pit.

The erasing laser beam is irradiated to the recording pit 19 basically in the same condition as the condition for initialization. Recording pit
As in the case of initialization, 19 is melted and gradually cooled to solidify and crystallize.

Next, a test example in which the information recording medium according to the present invention is manufactured and the characteristics are tested will be described.

Test Example The inside of the reaction vessel was adjusted to about 10 ⁻⁶ torr, and argon gas and nitrogen gas were introduced into the reaction vessel on a 1: 1 day, and the gas pressure in the vessel was adjusted to 5 mtorr. Under these conditions Si ₃ N ₄
RF power of 13.56 MHz was supplied to the target at an output of 300 W, and a Si ₃ N ₄ protective layer of about 1000 Å was formed on a polycarbonate substrate. Then, the supply of nitrogen gas was stopped, the gas pressure of argon gas was adjusted to 5 mtorr, and the RF power of 500 W was applied.
The surface of the Si ₃ N ₄ protective layer was sputter etched for about 2 minutes. In this case, the relationship between the magnitude of RF power and the surface roughness was previously known. Under these conditions, the surface roughness of the protective layer was about 80Å on average. Then, RF powers of 100 W and 30 W were supplied to the Sb target and the Te target, respectively, to deposit an Sb ₆₀ Te ₄₀ recording layer of about 800 Å on the Si ₃ N ₄ protective layer. Then, the surface of the recording layer was sputter-etched for about 2 minutes by RF power of 100 W, and the surface roughness was set to 100 Å on average. On top of this recording layer, under the same conditions as the protective layer described above, Si ₃ N
_{The four} main layers were formed to a thickness of 1000Å. This sample is taken out of the container 21, and after applying a UV curable resin on the main layer by a spinner, the resin is irradiated with UV rays to about 10 μm.
An auxiliary layer of m was formed to obtain an optical disc sample (this is referred to as sample A). By the same method, a sample in which each layer was formed in the same layer configuration as sample A without sputter etching treatment was prepared (this is referred to as sample B). The characteristics of these samples were evaluated by a dynamic characteristics evaluation device. A semiconductor laser with a wavelength of 830 nm was used, and during initialization, continuous light irradiation with an output of 5 mW was performed to crystallize the entire surface of the disk. The rotation speed of the disk at this time was 600 rpm. When recording, the rotation speed of the disk is 600 rpm as well.
Output is 10mW, pulse width is 100ns, duty ratio is 5
The recording layer was pulse-irradiated with 0% laser beam. During reproduction, the recording pit was irradiated with a laser having an output of 0.4 mW. In this case, sample A could obtain an AC signal with an amplitude of 70 mW. The degree of modulation at this time was 50%. On the other hand, in the case of sample B, a signal was not obtained at all as a result of irradiation with a laser beam of 0.4 mW. After this dynamic characteristic test, the laser beam irradiated portions of these samples A and B were cut out, only the recording layer was peeled off, and the structure was observed with a transmission electron microscope (TEM). Although the recording pits could be observed, in the sample B, only the crystallized track could be observed.

In this way, by making the interface between the recording layer and each protective layer uneven, the recording layer can be appropriately cooled, and the laser beam irradiation portion can be made amorphous.

In this example, the recording layer formed of SbTe was used, and the case where the protective layer formed of Si ₃ N ₄ was used was shown, but the thermal diffusion of the protective layer is not limited to this. It can be applied when the laser beam irradiation portion of the recording layer can be made amorphous by a slight adjustment. Further, not only the case of a recording layer that records and erases information by a phase change between a crystalline phase and an amorphous phase such as SbTe, but a recording that erases and records information by changing the phase between different crystalline phases. It can also be applied in the case of layers.

EFFECTS OF THE INVENTION According to the present invention, in the case of an information recording medium having a recording layer in which information is recorded and erased by being phase-changed by irradiation of a light beam, it is arranged so as to sandwich the recording layer. Since the interface with two protective layers is made uneven, the cooling rate of the recording layer becomes appropriate by changing the shape of the uneven portion according to the combination of the material of the recording layer and the material of the protective layer. Thus, the heat radiation amount of the protective layer can be finely adjusted. Therefore,
Even if the recording pit cannot be formed in the laser beam irradiation portion of the recording layer only by selecting the material for forming the protective layer, the recording pit can be effectively adjusted by finely adjusting the heat radiation amount of the recording layer in this way. Will be able to be formed.

[Brief description of drawings]

1 (a) and 1 (b) are sectional views showing an information recording medium according to an embodiment of the present invention, FIG. 2 is a schematic view showing a film forming apparatus for an optical disc, and FIG. 3 is a conventional information recording medium. FIG. 11; substrate, 12, 14, 15; protective layer, 13; recording layer, 18; laser beam, 19; recording pit

Claims (4)

[Claims] 1. A substrate, a recording layer in which information is recorded and erased by being phase-changed by irradiation with a light beam, a first protective layer formed between the substrate and the recording layer, and a recording layer. In an information recording medium having a second protective layer formed on the above, the interface between the first protective layer and the recording layer and the interface between the recording layer and the second protective layer are uneven. An information recording medium having a part. 2. The information recording medium according to claim 1, wherein the uneven portion has a height of 10 to 200Å. 3. The uneven portion is formed by sputter etching the surface of the first protective layer on the recording layer side and the surface of the recording layer on the second protective layer side. The information recording medium according to claim 1 or 2. 4. The second protective layer is a two-layer body comprising a main layer and an organic resin auxiliary layer formed thereon, and the second protective layer is a two-layer body. Any one of 3
The information recording medium described in the item.