JP3365519B2 - Phase change optical disk - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing information at high speed by causing a phase change between a crystal and an amorphous layer in a recording layer by a difference in irradiation laser power. The present invention relates to a phase-change type optical disc which can be recorded, reproduced, and erased at high density and has excellent repetition characteristics. 2. Description of the Related Art A phase change type optical disk has a recording layer
A material that undergoes a phase change between crystal and amorphous due to the difference in irradiation laser power is provided on one surface of a transparent substrate. This has the advantage that it is possible to record important information (hereinafter referred to as “overwrite”). As a recording material of a phase-change type optical disk capable of overwriting, an In—Se alloy (App
l. Phys. Lett. 50, 667, 198
7 years) or an In-Sb-Te alloy (Appl. Phys.
Lett. 50, 16, 1987), Ge-T
Chalcogen alloys such as e-Sb alloys are mainly used. When recording / erasing is actually performed using such a chalcogen alloy as a recording layer, the substrate is prevented from being deformed by the heat generated during recording / erasing, and the recording layer is prevented from being oxidized or deformed. In order to do so, usually, one or both directly under and above the recording layer, at least one selected from oxides, carbides, nitrides, fluorides, and sulfides of metals or metalloids Is provided. Of these protective layer materials, SiO _{2 is} used for ZnS.
When a protective layer is formed by adding a glass forming material such as
It is preferable because it has excellent heat resistance and adhesion to the recording layer. [0005] A recording layer made of a chalcogen alloy, a protective layer provided immediately below and / or immediately above the recording layer, and a reflective layer (Al alloy) serving also as a cooling layer provided on the side of the recording layer opposite to the substrate side. A three- or four-layer structure having a three-layer structure consisting of a film and a film on a transparent substrate is suitable for recording and erasing characteristics, and thus has become the mainstream of phase-change optical disks.
FIG. 4 shows a conventional general four-layer phase change type optical disk.
FIG. For such a three-layer or four-layer phase change optical disk, various proposals have been made with respect to an increase in the number of overwrite repetitions and an improvement in erasing characteristics. Japanese Patent Application Laid-Open No. 4-141488 discloses that a protective layer composed of ZnS and SiO ₂ is doped with nitrogen.
It is disclosed that a recording layer made of -Te-Ge alloy containing nitrogen is disclosed. [0006] However, in the method of adding nitrogen to the protective layer, the archival characteristics (stability of amorphous pits under high temperature and high humidity) and reproduction light stability ( However, there is a problem that the stability of the amorphous pits with respect to repeated reproduction is reduced. Also, Sb-Te-G
In a method of forming a recording layer using nitrogen in an e-based alloy, usually, a film is formed by a sputtering method using an Sb-Te-Ge-based alloy as a target and using a mixed gas of Ar gas and nitrogen gas. . When forming a film by the sputtering method,
In addition to the components of the target, impurities such as residual gas components may enter the film, and the presence of such impurities may change the film quality due to repetition of overwriting and exhibit characteristics deviating from the initial design characteristics. . And Sb
In this method, in which nitrogen is present in the entire recording layer made of a Te-Ge alloy, the bonding state between nitrogen and each of the recording layer material elements of Sb, Te, and Ge is changed between the film formation (initial) and the overwriting. Is repeated, and a large difference occurs in the recording sensitivity between, for example, one-time recording and 100 times of overwriting, so that the recording / erasing is repeated about 100 times until the recording sensitivity is stabilized. There was a problem that it became necessary. The present invention has been made in view of such problems of the prior art, and it has been found that the overwrite repetition count can be reduced while ensuring archival characteristics, reproduction light stability and recording sensitivity stability. It is an object of the present invention to provide a phase-change optical disk having an increased erasing characteristic and improved erasing characteristics. In order to achieve the above object, a phase change type optical disk according to the present invention comprises a transparent substrate and an irradiating laser power formed on one surface of the substrate. A recording layer made of a material in which a phase change between a crystal and an amorphous occurs due to a difference between the recording layer and a protective layer formed on one or both of the recording layer and the substrate and outside or outside the recording layer. In the phase change optical disk, the material of the protective layer
Is selected from metal, metalloid oxides, fluorides and sulfides.
A mixture of at least one of the above and ZnS,
Wherein between the protective layer and the recording layer, the protective layer material and Ri Na <br/> from nitrogen, in which the thickness is characterized in that a following auxiliary layer 10 nm. Here, when a protective layer is provided both between the recording layer and the substrate and outside the recording layer (that is, when an upper protective layer and a lower protective layer are provided), the upper protective layer and the recording The protective layer material and nitrogen in one or both of the layers and / or between the lower protective layer and the recording layer
An auxiliary layer having a thickness of 10 nm or less is provided. FIG. 1 shows an example of the phase change optical disk of the present invention. This example is provided with both an upper protective layer and a lower protective layer. A lower protective layer 2 is provided on a transparent substrate 1, a recording layer 3 is provided thereon, and a thickness composed of a protective layer material and nitrogen is provided. An auxiliary layer 4 having a thickness of 10 nm or less ;
An upper protective layer 5, a reflective layer 6, and an ultraviolet curable resin layer 7 are sequentially laminated. Conventionally known materials can be used for forming each layer. As the transparent substrate 1, polycarbonate, glass, or the like, which has good optical characteristics, high mechanical strength, and excellent dimensional stability, is suitable. As a material of the recording layer 3,
In-Sb-Te, Ge-Te-Sb, In-Sb-T
1, Ge-Te-Sn-Au, Ge-Te-Sb-Pd
Preferred are Te or Se based alloys. [0012] Material cost of the protective layer 2 and 5, a metal or metalloid
At least one selected from oxides, fluorides, and sulfides
And ZnS, for example, SiO ₂ , Si
_{O, Ta 2 O 5, ZrO} 2 oxide such, fluorides such M gF _2, and SmS, and at least one selected from the sulfides such as SrS, a mixture of ZnS are preferred. The auxiliary layer 4 made of the protective layer material and nitrogen is formed, for example, by the following method. After forming the lower protective layer 2 and the recording layer 3 on one surface of the substrate 1 by ordinary means, a mixture of Ar gas (a general film forming gas) and nitrogen gas is used as a target for the protective layer material. A film (auxiliary layer 4) made of a protective layer material and nitrogen is formed by a sputtering method using a gas. At this time,
Nitrogen gas may be introduced into the apparatus from a gas line of a different system from Ar gas, or may be introduced as a mixture with Ar gas. Then, after that, the upper protective layer 5 is formed to have a predetermined thickness by performing sputtering using only the Ar gas that does not contain nitrogen gas, using the protective layer material as a target. When an auxiliary layer is provided between the lower protective layer 2 and the recording layer 3, the same operation as described above is performed after the lower protective layer 2 is formed and before the recording layer 3 is formed. In the above-mentioned method, the nitrogen content in the formed auxiliary layer 4 is determined by the partial pressure of nitrogen gas in the film forming gas. A suitable value for the nitrogen content in the auxiliary layer 4 slightly varies depending on the target composition and the film forming conditions of the recording layer 3 and the protective layers 2 and 5, but is preferably 10 to 80 μto
rr Ru Der. Further, the film thickness of the auxiliary layer consisting of a protective layer material and nitrogen, and 10nm or less. If the film thickness exceeds 10 nm, the same problem as in the case where nitrogen is contained in the entire protective layer will occur. In the present invention, the protective layer is formed of a metal or a semimetal.
At least one selected from oxides, fluorides and sulfides of
A mixture of a seed and ZnS, and a protective layer material and nitrogen having a thickness of 1 between the protective layer and the recording layer.
By providing an auxiliary layer of 0 nm or less , that is, by allowing nitrogen to be present only on the interface between the protective layer and the recording layer, not on the entire protective layer adjacent to the recording layer, archival characteristics and reproduction light stability can be improved. Character can be secured,
If the stability of the recording sensitivity with repeated overwriting cannot be ensured as in the method of including nitrogen in the entire recording layer
Needless to say , stable amorphous pits can be formed. Hereinafter, the present invention will be described in detail with reference to examples. Example 1 A phase-change optical disk having a layer structure shown in FIG. 1 was manufactured by the following procedure. First, 130 mm in diameter and 1.
A polycarbonate substrate 1 having a diameter of 2 mm and a groove having a pitch of 1.6 μm formed on one side is placed in a chamber, and a Zn (Zn) is formed on the groove side by RF (high frequency) sputtering.
Consisting of S and SiO ₂ (ZnS: SiO = 80: 2
0) A 180 nm protective layer 2 was formed using a target. Next, on the protective layer 2, to form a recording layer 3 of 25nm by targeting Sb-Te-Ge-based alloy. The recording layer 3 has a partial pressure of Ar gas of 10 m on the recording layer 3.
Sputtering was performed using a target composed of ZnS and SiO ₂ (ZnS: SiO = 80: 20) at a torr and a nitrogen partial pressure of 20 μtorr to form auxiliary layers 4 containing 3, 5, 10, and 15 nm of nitrogen, respectively. Thereafter, the protective layer 5 made of ZnS and SiO ₂ is removed by completely removing nitrogen to form a 20.
nm. Then, either Al alloy on the protective layer 5
A reflective layer 6 having a thickness of 150 nm was formed. UV on this
A line-curing resin is applied by spin coating to a thickness of 5 μm.
The resin layer 7 was formed by irradiating the resin with ultraviolet rays to cure the resin layer 7 . In addition, as a comparative example, a supplement as shown in FIG.
Without forming the auxiliary layer 4, the partial pressure of Ar gas was
10mtorr, ZnS and SiO ₂ in the nitrogen partial pressure 20μtorr
(ZnS: SiO = 80: 20) target
Sputtering is performed using a 20 nm protective layer 5a.
Was also prepared. Each sample of the phase-change optical disk obtained in this manner is applied to a driving device and rotated at a linear velocity of about 5 m / s. After overwriting the signal 100 times, the read power (1.
8mW), and after measuring the CNR, irradiating the laser with the read power was repeated.
FIG. 3 is a graph showing the results obtained by measuring the CNR even after 100,000 times and examining the amount of CNR reduction. Further, the same measurement for the disc of Comparative Example, also shown in FIG. 3 also result. As can be seen from the graph, the disk having the auxiliary layer 4 has a smaller decrease in CNR than the disk without the auxiliary layer 4 and has excellent reproduction light stability.
In particular, the effect is high when the thickness of the auxiliary layer 4 is 10 nm or less. As described above, according to the present invention, the protective layer is formed of a metal or metalloid oxide, fluoride or sulfur.
Of ZnS with at least one selected from oxides
And an auxiliary layer having a thickness of 10 nm or less made of a protective layer material and nitrogen is provided between the protective layer and the recording layer, that is, instead of the entire protective layer adjacent to the recording layer, The presence of nitrogen only on the interface between the protective layer and the recording layer enables archival characteristics and reproduction light stability .
Improvements have been made, yet is contained nitrogen throughout the recording layer
Recording sensitivity with repeated overwriting as in the method
A phase change optical disk which does not cause deterioration of the stability of the optical disk can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of a layer structure of a phase change optical disc according to the present invention. FIG. 2 was prepared as a comparative example in <Example 1>.
FIG. 3 is a cross-sectional view illustrating a layer structure of a phase change optical disc. FIG. 3 shows the CNR reduction amount and the reproduction light illumination in <Example 1>.
It is a graph which shows the relationship with the number of shots. FIG. 4 is a layer structure of a conventional general phase-change optical disc.
It is sectional drawing which shows (four-layer structure). [Description of Signs] 1 Substrate 2 Protective layer 3 Recording layer 4 Auxiliary layer 5 Protective layer 5a Protective layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-14635 (JP, A) JP-A-3-232133 (JP, A) JP-A-3-168945 (JP, A) JP-A-63-1988 166046 (JP, A) JP-A-62-298037 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24

Claims (1)

(57) [Claim 1] A transparent substrate and a material formed on one surface of the substrate, which undergoes a phase change between crystal and amorphous due to a difference in irradiated laser power. In a phase change optical disc comprising a recording layer consisting of: and a protective layer formed between the recording layer and the substrate and / or outside the recording layer, the material of the protective layer is metal. Or semi-metal oxide, fluoride
And at least one selected from sulfides, ZnS,
A mixture of, between the protective layer and the recording layer, the protective layer material and the nitrogen and Ri Na <br/> from a phase change type optical disk, wherein the thickness is provided below the auxiliary layer 10nm .