JP2913521B2 - Optical recording medium, sputtering target for optical recording medium, and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording, reproducing, and erasing information at a high density and a large capacity by a laser beam or the like, a sputtering target used for producing the same, and a method for producing a sputtering target. .

[0002]

2. Description of the Related Art Optical discs as optical recording media are classified into write-once discs and rewritable discs according to the recording thin film used. The former write-once disc is capable of recording and reproduction, but once data is written, it cannot be erased, and data cannot be written again. On the other hand, the latter rewritable disc can rewrite data in the same data area many times.

The write-once disc records data on a recording thin film by irradiating a laser beam, and reproduces data by detecting a change in the amount of light reflected from the recording thin film by a photodiode.

The recording thin films used here are Te and TeO ₂
Is a thin film composed of a component of TeO _x (0 <x <2.0), whose main component is an amorphous state (amorphous state) when the film temperature is increased by irradiation with laser light.
From the crystalline state to the crystalline state. Data recording is performed using this phenomenon. On the other hand, this recording thin film cannot change from a crystalline state to an amorphous state.
Therefore, recording / reproduction is possible with a write-once disc,
It cannot be rewritten.

On the other hand, magneto-optical recording disks and phase-change recording disks are the mainstream rewritable disks.
Some magneto-optical recording disks use an amorphous alloy (amorphous alloy) composed of a rare earth transition metal as the recording thin film.
Is used. Here, in the magnetic thin film, the film temperature increases in a portion irradiated with the laser beam, and the coercive force decreases. For this reason, when a weak external magnetic field is applied to such a magnetic thin film, the portion undergoes magnetization reversal and is held as a spot-shaped magnetic domain. Therefore, data recording is performed by utilizing this phenomenon.

[0006] In reproducing, the deflection surface of the laser beam is rotated depending on the direction of magnetization. Therefore, utilizing this phenomenon, a laser beam having a lower power than that at the time of recording is applied to the magnetic thin film to deflect the laser beam. This is done by detecting the change state of

[0007] The change state of the deflection plane in the laser light is detected by using an element called an analyzer (linear polarizing plate) that changes the rotation of the polarization plane into a change in light intensity. On the other hand, the spot-shaped magnetic domain whose magnetization has been inverted can be returned to the original state by applying a strong magnetic field, and thus can be rewritten.

[0008] In the phase change recording disk, as a recording thin film material, S.T. G proposed by R Ovshinsky and others
chalcogen materials such as e ₁₅ Te ₈₁ Sb ₂ S ₂ , As ₂ S ₃ , As ₂ S
A thin film comprising a combination of a chalcogen element such as e ₃ or Sb ₂ Se ₃ and an element of Group 9 or 8 of the periodic table is known.

As a method of recording information on these thin films with a laser beam and erasing the information, a laser beam focused to about 1 μm is applied to a recording thin film which has been initialized to a crystalline state in accordance with the information. Irradiation with modulation, heating and melting above the melting point, rapid cooling to an amorphous state, recording data as a mark, and recording the amorphous thin film above its glass transition point (lower than the melting point) After heating to a temperature that is easy to crystallize, the crystal can be crystallized by maintaining a predetermined time to erase data.

[0010] At the time of reproduction, similarly to the write-once disk, a change in the amount of light reflected from the recording thin film is detected by a photodiode. Therefore, recording / reproduction and rewriting can be performed on the phase change recording disk.

FIG. 2 is a longitudinal sectional view showing the structure of a conventional rewritable optical recording medium employing a phase change recording system. The rewritable optical recording medium has a thin disk shape having a center hole 18 as a whole, and has a multilayer structure in a longitudinal section as shown in the figure. The rewritable recording medium is irradiated with laser light in the direction indicated by arrow A.

In the multilayer structure shown here, a substrate made of a transparent resin material is arranged from below in the direction indicated by arrow A in the figure.
11, a first protective film 12 made of a dielectric, a recording thin film 13, a second protective film 14 made of a dielectric, a reflective film 1 made of a metal thin film
5, the adhesive 16, and the protection plate 17 are formed in a laminated state.

Here, as the recording thin film 13, for example, Te-
When a Ge—Sb alloy thin film is used, its crystallization speed is high, so that information can be easily rewritten by a single laser beam (generally called overwriting).

Further, the formation of the recording thin film described above is performed by a vacuum evaporation method or a sputtering method.
In the vacuum deposition method, the inside of the vacuum layer is evacuated to 10-4 Torr or less,
The material is heated and evaporated therein, and deposited on a substrate to form a thin film.

On the other hand, in the sputtering method, a cathode serving as an evaporation source (this is called a sputtering target)
Then, positively charged particles are bombarded and ejected from the cathode, and such atoms are deposited on a substrate to form a thin film.

[0016]

When a rewritable disc using the phase change recording method is used, recording and erasing are repeated, so that the number of phase changes in the recording thin film becomes extremely large, which is necessary for reading information. The problem that the signal quality fluctuates occurs.

This is because a severe thermal operation in which the recording thin film 13 is rapidly heated to 400 ° C. or more and then rapidly cooled is repeated by a laser beam in a minute area of about 1 μm. This is because thermal damage to the thin film itself, and also to the protective films 12 and 14 or the substrate 11 in contact with the upper and lower surfaces of the recording thin film, may result.

In particular, in order to prevent thermal damage to the recording thin film 13, it is necessary to sufficiently cool the recording thin film heated to a high temperature in a short time. As a countermeasure, for example, it is conceivable to increase the thermal conductivity of the protective films 12 and 14 in contact with the recording thin film to enhance the cooling effect.

The protective films 12 and 14 are used as heat-resistant layers for preventing the substrate 11 or the protective plate 17 from being thermally deformed, and generally use a dielectric material. Here, as a dielectric material having high thermal conductivity, there is Ta ₂ O _5, which is promising because it can be easily formed into a thin film and has a high refractive index. When Ta ₂ O ₅ is used for the protective films 12 and 14, the thermal conductivity of the protective films is high and the recording thin film 13 can be cooled in a short time, so that it can be expected that thermal damage to the recording thin film can be prevented.

Here, the recording thin film 13 repeats heating and cooling more rapidly than recording and erasing. The protective films 12 and 14 provided on both sides of the recording thin film repeat expansion and contraction under the influence of heating and cooling of the recording thin film. The heating and cooling regions are performed only at a local portion irradiated with a laser beam narrowed down to about 1 μm. As a result, distortion occurs in the protective films 12 and 14, and T
a ₂ O ₅ in the case of using repeated resulting in increased noise damage microscopic cracks, separation and the like due to high internal stress is generated record, a problem resulting in deterioration in the reproduction characteristics.

When Ta ₂ O ₅ is used as the protective films 12 and 14, not only deterioration of the recording and erasing characteristics but also long-term storage in a high-temperature and high-humidity environment results in high internal stress. There is also a problem that peeling or the like occurs.

An object of the present invention is to solve the above-mentioned problems and to provide an optical recording medium having excellent repetition characteristics many times, a sputtering target for the optical recording medium, and a method of manufacturing the same.

[0023]

According to the present invention, information is recorded,
At least one of the recording thin films to be erased includes Ta ₂ O ₅ and Si ₃ N ₄
Wherein the sputtering target for an optical recording medium contains Ta ₂ O ₅ and Si ₃ N ₄ , and the sputtering target for the optical recording medium contains Ta ₂ O ₅ and Si.
₃ N ₄ of the powder mixture and forming by hot pressing.

[0024]

[Action] heat-resistant temperature as a protective film according to the present invention, although the thermal conductivity has a feature that high, relative to Ta ₂ O ₅ having the disadvantage of internal stress has a crystalline structure is high, Si ₃
By mixing N ₄ , a film having an amorphous structure can be formed, and the internal stress can be reduced from か ら to 1/1 as compared with a single Ta ₂ O _5.
5, and the released oxygen combines with Si to form a chemically stable film, so that thermal damage due to rapid heating and cooling accompanying repetition of recording and erasing can be suppressed.
Cracks and peeling can be prevented.

By changing the mixing ratio of Si ₃ N ₄ to Ta ₂ O _5, the thermal conductivity of the protective film can be changed, and the cooling rate of the recording thin film can be adjusted.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a longitudinal sectional view showing the configuration of the optical recording medium according to the present invention. The optical recording medium has a thin disk shape having a center hole 8 as a whole, and has a multilayer structure having a vertical section as shown in the figure.

This optical recording medium is irradiated with laser light in the direction indicated by arrow A. For the multilayer structure, a transparent resin substrate 1 made of a polycarbonate resin substrate or a glass substrate in which laser light guide grooves or pit rows are previously formed from below in the direction indicated by arrow A in the figure. This substrate 1 is made of Ta ₂ O ₅ and 20 mol of Si ₃ N ₄ .
The first protective film 2 mixed with 1% is formed to about 1500 angstroms. On this first protective film 2, Te, Ge,
A recording thin film 3 made of Sb is formed to a thickness of about 200 angstroms.

Further, a first protective film 2 is formed on the recording thin film 3.
Then, a second protective film 4 of the same material is formed to about 300 Å. To improve the recording sensitivity on the second protective film 4 by utilizing the multiple interference of laser light, Au, Al,
A reflective film 5 made of a metal such as Cu or NiCr is formed to a thickness of about 1000 angstroms. Next, a protective plate 7 is bonded with an adhesive 6 to protect these thin films.

As a method for forming each of the above thin films, a vacuum evaporation or sputtering method can be used. Where the first
As a sputtering target for forming the second protective films 2 and 4, it is preferable to use Ta ₂ O ₅ containing Si ₃ N ₄ .

In the method of manufacturing the sputtering target, powders of Ta ₂ O ₅ and Si ₃ N ₄ are weighed so as to have a target composition, and mixed with a raikai machine or a ball mill to form a uniform mixture. This mixture is put in a mold, pressurized and heated, that is, hot pressed to complete the mixture.

In the configuration of FIG. 1, recording and erasing are about 1 μm.
This is performed by irradiating the recording thin film 3 with the laser beam focused on the spot in the direction of arrow A to heat a minute area of the recording thin film 3. At this time, although the recording thin film 3 has an area of about 1 μm, the recording thin film 3 used in this embodiment has Te, Ge,
In the case of the alloy material b, for example, it is rapidly heated to 600 ° C. or higher during recording, and is rapidly cooled after recording.

With such rapid heating and cooling of the recording thin film 3, the first and second protective films 2 and 4 in contact with the recording thin film 3 are also heated and cooled. As described above, the first and second protective films repeatedly heat and cool rapidly with the repetition of recording and erasing, and cracks and peeling may occur in the heated area due to the thermal shock depending on the material of the protective film. is there. For example, when Ta ₂ O ₅ is used for the protective film, due to the property that Ta ₂ O ₅ has a large internal stress, minute cracks and peeling are likely to occur due to thermal shock accompanying repetition of recording and erasing. This is considered to be related to the large internal stress of Ta ₂ O ₅ .

On the other hand, Ta ₂ O ₅ according to the present embodiment is
₃ Repeat minute cracks and peeling in the thermal shock due to the N ₄ protective film 2 and 4 were mixed in recording and erasing does not occur. Furthermore, it was stable for long-term storage in a high-temperature, high-humidity environment.

While a thin film of Ta ₂ O ₅ alone has a crystalline structure, a thin film obtained by mixing Ta ₂ O ₅ with Si ₃ N ₄ has an amorphous structure and has an internal stress of Ta ₂ O _5. 1/2 to 1/5 of
It turned out to be smaller. It is considered that this was effective for minute cracks and peeling. By mixing Ta ₂ O ₅ with Si ₃ N ₄ , a protective film having an amorphous structure can be obtained and the internal stress can be reduced. However, when Si ₃ N ₄ is reduced to 5 mol or less. Has an internal stress close to that of Ta ₂ O ₅ alone and its effect is small.

When Si ₃ N ₄ is more than 50 mol,
Not only the deposition rate becomes slow, but the strain in the film is large, especially when a multilayer film is formed on a plastic substrate.
When subjected to an environmental test at a high temperature and a high level, peeling and the like are observed, which is not good.

From the above, it is appropriate that the amount of Si ₃ N ₄ with respect to Ta ₂ O ₅ is in the range of 5 mol% to 50 mol%. As described above, in this embodiment, the first and second protective films 2 and 4 are made of Ta ₂ O.
_{Since a} mixture of ₅ and Si ₃ N ₄ is used, a thin film having an amorphous structure is formed, and the internal stress of the thin film is reduced, so that cracks and peeling are generated even when recording and erasing are repeated many times. Therefore, the repetition characteristics are stable, and even when stored for a long period of time in a high-temperature, high-humidity environment, it is stable without peeling or the like.

The optical recording medium comprises a first protective film 2, a recording thin film 3, a second protective film 4, and a reflective film 5 on a substrate 1.
Are sequentially laminated, while the thickness of the second protective film 4 is
The thickness of the first protective film 2 is smaller than the thickness of the first protective film 2.
The stability by recording and erasing at 30 nm is secured.

[0038] The first above description, but is for the case of using the second protective film 2 and 4 sputtering target obtained by mixing Si ₃ N ₄ to Ta ₂ O ₅ as a method for forming, Ta ₂ O ₅ and Si ₃ N ₄ may be formed by sputtering together using respective targets. Alternatively, it may be formed by a reactive sputtering method of air, oxygen and nitrogen gas using a Ta target and a Si target.

[0039]

As described above, the optical recording medium of the present invention uses a sputtering target for an optical recording medium, and is made of a material obtained by mixing Ta ₂ O ₅ and Si ₃ N ₄ as protective films provided on both sides of the recording thin film. By forming a thin film on a substrate, it becomes an amorphous thin film, the internal stress of this thin film can be reduced, and cracks and peeling caused by thermal shock caused by repeated recording and erasing, and high temperature and high humidity Peeling or the like when used or stored for a long time under the above environment can be prevented.

Therefore, even if rewriting is performed many times, stable recording and erasing characteristics can be obtained without deterioration of signal quality. Further, since the quenching effect of the recording thin film is remarkably improved by reducing the thickness of the second protective film 4 between the recording thin film 3 and the reflection film 5, uniform amorphousization, that is, uniform recording marks Can be formed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a configuration of an optical recording medium according to one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing the configuration of a conventional rewritable optical recording medium employing a phase change recording method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... 1st protective film, 3 ... Recording thin film, 4
... Second protective film, 5 ... Reflective film, 6 ... Adhesive, 7 ...
Protective plate, 8 ... Center hole.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshiaki Furukawa 1006 Kazuma Kadoma, Kadoma-shi, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-3-5929 (JP, A) JP-A-4 -331759 (JP, A) JP-A-55-104972 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/24 534 C23C 14/34

Claims (7)

(57) [Claims] 1. a property of melting by heating at a temperature higher than a melting point by irradiation with a laser beam, and a property of becoming an amorphous state by further quenching; A recording thin film having a property of being changed from the amorphous state to a crystallized state by being gradually cooled, and a protective film made of a mixture of Ta ₂ O ₅ and Si ₃ N ₄ is provided on at least one of the recording thin films; An optical recording medium, characterized in that: 2. A first protective film, a recording thin film, and a recording thin film on a substrate.
2. The optical recording medium according to claim 1, wherein a second protective film made of the same material as the first protective film and a reflective film are sequentially laminated. 3. A first protective film on a substrate, a recording thin film,
A second protective film made of the same material as the first protective film and a reflective film are sequentially laminated, and the thickness of the second protective film is
2. The optical recording medium according to claim 1, wherein the thickness is smaller than the first protective film, and the thickness of the second protective film is at most 30 nm. 4. The optical recording medium according to claim 1, wherein a material made of Te, Ge, and Sb is used as the recording thin film. 5. The first protective film and the second protective film are both Ta ₂
O ₅ and Si ₃ made of a mixture of N _4, an optical recording medium according to claim 1, wherein the molar fraction the Si ₃ N ₄ is characterized in that a 5 to 50 mol%. 6. Ta ₂ O ₅ and Si ₃ to form a protective film.
Sputtering target for an optical recording medium characterized that it contained N _4. 7. A method for producing a sputtering target for an optical recording medium, comprising hot pressing a powder mixture of Ta ₂ O ₅ and Si ₃ N ₄ to form a formed body.