JPH07111786B2 - Optical recording medium, protective film for optical recording medium, and manufacturing method of protective film - Google Patents

Description

The present invention relates to an optical recording medium capable of recording / reproducing and erasing information with a high density and a large capacity by a laser beam or the like, a protective film for an optical recording body, and a method for producing the protective film. It is about.

Conventional technology For optical disk memory, Te and TeO ₂ are the main components
There is a write-once disc that uses a TeO _x (0 <x <2.0) thin film. Further, an erasing disk capable of repeatedly recording and erasing is being put to practical use. This erasing disc is one in which a recording thin film is heated by laser light, melted, and rapidly cooled to be amorphous so that information can be recorded, and by heating and slowly cooling these, erasing can be performed by crystallization. However, as a material for this recording thin film, the chalcogen material Ge _{15 by} SROvshinsky et al.
Te ₈₁ Sb ₂ S ₂ etc. are known. In addition, a chalcogen element such as As ₂ S ₃ or As ₂ Se ₃ or Sb ₂ Se ₃ and Group V of the periodic table or
Thin films and the like made of a combination of group IV elements such as Ge are widely known. These thin films can be formed on a substrate provided with a groove for laser light guide and used as an optical disc. A method of recording information on these discs with laser light and erasing the information is to crystallize a thin film in advance and subject the laser light focused to about 1 μm to intensity modulation in accordance with the information. When the disk-shaped recording disk is rotated and irradiated, the peak power laser beam irradiation site is heated to a temperature equal to or higher than the melting point of the thin film and rapidly cooled,
Information can be recorded as an amorphized mark. Further, this modulated bias power laser light irradiation site has a function of erasing the recorded signal information by raising the temperature above the crystallization temperature of the thin film and can be overwritten. As described above, the recording thin film is heated to the melting point or higher and the crystallization temperature or higher by the laser beam. For this reason, a dielectric layer having excellent heat resistance is generally provided on the lower surface and the upper surface of the recording thin film as a protective layer for the substrate and the adhesive layer.
Due to the heat conduction characteristics of these protective layers, temperature rise and quenching,
Since the characteristics of slow cooling change, the characteristics of recording and erasing can be determined by selecting the material of the protective layer.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention A first problem in an information recording and erasable overwrite recording medium that uses a means of heating and heating a thin film, melt quenching amorphization and heating and temperature rising crystallization is The second issue is the cycle characteristics of recording and erasing. Regarding the erasing characteristics, the melting point of a typical amorphous film containing Te is 400
Wide temperature range from ℃ to 900 ℃. Crystallization can be performed by irradiating these thin films with a laser beam and gradually raising the temperature and cooling. This temperature is generally in the crystallization temperature range below the melting point. When the crystallized laser beam of high power level is applied and heated to a temperature higher than its melting point, that portion is melted and rapidly cooled, and is amorphized again to form a mark. If amorphization is selected as the recording mark, this mark is formed by melting and rapidly cooling the recording thin film, so the faster the cooling rate, the more uniform the amorphous state is obtained and the signal amplitude is increased. improves. When the cooling rate is slow, a difference occurs in the degree of amorphization between the center and the periphery of the mark. Next, at the time of crystallization and erasing, the amorphous mark portion already recorded by laser irradiation is heated to a temperature above the crystallization temperature to be crystallized to erase the mark. At this time, when the marks are uniformly crystallized, the erasing property is improved, but when the recording marks are not uniform, the crystallization and erasing state becomes non-uniform and the erasing property is deteriorated. Regarding the cycle characteristics of recording and erasing, there is thermal damage to the disk substrate or the protective layer due to a large number of repeated heating and cooling. When the disk substrate or the protective layer is thermally damaged, there is a problem in that noise is increased in the cycle of recording / reproducing and erasing and the cycle characteristics are deteriorated. An object of the present invention is to provide an optical disc having excellent recording / erasing characteristics and stable cycle characteristics.

Means for Solving the Problems According to the present invention, a first protective layer, a recording thin film, a second protective layer, and a reflective layer are sequentially formed on one surface of a transparent substrate and thermally recorded by irradiation with a laser beam or the like. In a medium for recording and erasing the state by changing the optical state of a thin film, a dielectric layer containing nitrogen in a mixed film of ZnS and SiO ₂ is used as the first and second protective layers.

The action, that is, by using a dielectric material containing nitrogen in a mixed film of ZnS and SiO ₂ as a protective layer, the dielectric material is ZnS and SiO ₂
It becomes a mixture of the mixed film of and the nitride of Zn, Si, etc., so that it becomes a dense and film with few released Zn, Si, etc., that is, with few defects, and the mechanical strength is improved and many times of recording / erasing are performed. Has a great effect on the repetition of. In addition, the thermal conductivity of the protective layer itself also becomes large, which has the effect of increasing the cooling rate of the recording thin film, and the thickness of the second protective layer is made thin so that the reflective layer made of a metal layer and the recording thin film are separated. Combined with the rapid cooling effect brought by approaching, the recording mark obtained by heating and quenching the recording thin film becomes a uniform amorphous state, resulting in a non-uniform state during crystallization erasing that occurs when the recording mark is non-uniform. It is possible to prevent the occurrence and improve the erasing property.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 1 denotes a disk substrate, which is made of a resin substrate such as polycarbonate. This disk substrate 1 is a resin substrate on which a groove for guiding laser light is formed in advance or
It may be a glass plate having grooves formed by the 2P method or a substrate having grooves directly formed on the glass plate. 2 is the first protective layer, ZnS-SiO
The mixed film of ₂ is composed of a dielectric pair containing nitrogen and has a film thickness of about 150 nm. A recording thin film 3 is an alloy thin film made of Te-Ge-Sb and has a film thickness of about 30 nm. The second protective layer 4 is made of the same material as the first protective layer 2 and has a thickness of about 20 nm. Reference numeral 5 is a reflective layer made of Al and has a film thickness of about 60 nm.
Is. Reference numeral 6 is a protective plate, and the disk substrate 1 is made of an adhesive material 7.
Pasted on. In the configuration shown in the drawing, recording / erasing and reproduction are performed by irradiating a laser beam whose intensity is modulated in accordance with information and detecting reflected light in the direction of arrow 8. Here, the first and second protective layers 2 and 4 are ZnS-S.
The iO ₂ mixed film has a SiO ₂ ratio of 20 mol%. The present invention is not limited to this, and a ZnS—SiO ₂ mixed film can obtain the above-mentioned effects by including nitrogen. However, if the ratio of SiO ₂ is less than 5 mol%, ZnS is
effect obtained with iO ₂ when mixed, i.e. the effect of reducing the crystal grain size becomes small, when the above 50 mol%, since those properties of the SiO ₂ film is increased, SiO ₂
It was suitable to set the ratio of 5 to 40 mol%.
As a method of forming the ZnS-SiO ₂ mixed film is generally a vacuum deposition or sputtering method is used, in this embodiment by using a sputtering method using a mixed gas of argon and nitrogen. At this time, the partial pressure of nitrogen is important in determining the film quality, but the partial pressure of nitrogen during sputtering is 1.5 × 10 ^-5 to 1.5.
A range of x10 ^-3 Torr was suitable. The reason for this is 1.5 × 10 ^-5 T
When the partial pressure of nitrogen was made smaller than that of orr, the effect of the sputtering method using the mixed gas of argon and nitrogen became smaller. That is, it is difficult to form a mixture of a ZnS-SiO ₂ mixed film and a nitride, particularly a nitride. Conversely, 1.5 × 10 ^-3 T
If the partial pressure of nitrogen is made higher than that of orr, the above-mentioned ratio is appropriate because the problem that the film formation efficiency during sputtering is lowered depending on the partial pressure of nitrogen occurs. Further, the film thickness of the second protective layer 4 is thinned to about 20 nm, but this brings the reflective layer 5 serving as a heat diffusion layer and the recording thin film 3 close to each other, and the heat of the recording thin film 3 at the time of recording / erasing rapidly. Then, it is transmitted to the reflective layer 5, and is effective in rapidly cooling the recording thin film 3. With the disk configuration of this embodiment, the outer diameter is 130 nm, 1800r
The overwrite characteristics of the f1-3.43MHz signal and the f2-1.0MHz signal were measured at pm rotation. Overwrite is the modulation between high power level of 16mW and low power level of 8mW by laser light of about 1μm with one circle spot, forms amorphized marks at high power level, and does not use low power label. The simultaneous erasure method was used to crystallize and erase the crystallized marks. As a result, the C / N ratio of the recording signal was 55 dB or more, and the overwrite erasing rate was 30 dB or more as the erasing characteristic. Regarding the overwrite cycle characteristics, the bit error rate characteristics were measured, and as a result, no deterioration was observed for more than 1000000 cycles.

As described above, Zn is used as the protective layer on both sides of the recording thin film as described above.
By including nitrogen in the mixed film of S—SiO _2, the following effects can be obtained.

(1) The dielectric becomes a mixture of ZnS and SiO ₂ mixed film and nitride such as SiN, and becomes a dense film with less liberated Si etc., that is, fewer defects, improving the mechanical strength of the protective layer. To do.

(2) The recording signal amplitude is increased and the C / N ratio is improved to 55 dB or more.

(3) Recording marks are uniform and overwrite erase rate is 30 dB
Improves above.

(4) By increasing the cooling rate during recording / erasing, thermal shock during multiple cycles can be reduced and cycle characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a partially omitted sectional view of an optical information recording medium in one embodiment of the present invention. 1 ... Disk substrate, 2 ... First protective layer, 3 ... Recording thin film, 4 ... Second protective layer, 5 ... Reflective layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsumi Kawahara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-63-276724 (JP, A)

Claims (8)

[Claims] 1. A first protective film on one surface of a transparent substrate, and when irradiated with a laser beam, the energy is absorbed to raise the temperature, melt, quench, and become amorphous. A recording thin film having a property of crystallizing by raising the temperature of a crystalline state, a second protective film, an optical recording medium in which a reflective layer is sequentially formed, wherein the first and second protective layers are ZnS. And an SiO ₂ mixed film, wherein at least one protective film contains nitrogen. 2. The second protective layer is thinner than the first protective layer,
The optical recording medium according to claim 1, wherein the film pressure is 30 nm or less. 3. The optical recording medium according to claim 1, wherein a material composed of Te, Ge and Sb is used as the recording thin film. 4. The SiO ₂ ratio of a mixed film of ZnS and SiO ₂ is 5 to 40 mol%.
The optical recording medium according to claim 1, wherein 5. A protective film for an optical recording medium, characterized in that a mixed film of ZnS and SiO ₂ contains nitrogen. 6. The SiO ₂ ratio of a mixed film of ZnS and SiO ₂ is 5 to 40 mol%.
The protective film for an optical recording medium according to claim 5, wherein 7. A method for producing a protective film for an optical recording medium, characterized in that a protective layer made of a mixed film of ZnS and SiO ₂ is formed by a sputtering method using a mixed gas of argon and nitrogen. 8. The partial pressure of nitrogen when forming the protective layer is 1.5 × 10 5.
The method for producing a protective film for an optical recording medium according to claim 7, wherein the range is from ^{-5 to} 1.5 x 10 ^-3 Torr.