JP2002190137A - Laminated body and optical disc using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated body with small residual stress by thermal expansion and an optical disc using it. SOLUTION: 1) The laminated body is one having a substrate and a functional membrane and is characteristic of a stress relaxing layer having a thermal expansion coefficient that is a mean between the thermal expansion coefficient of the substrate and the thermal expansion coefficient of the functional membrane between the substrate and the functional membrane. 2) The disc is one including the laminated body shown in 1) as a part of layer components. 3) The disc is one laminating a phase change recording layer, an upper dielectric layer, and a reflex radiating layer in addition to a lower dielectric layer of the functional membrane, followed by the substrate and the stress relaxing layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminate having a small residual stress due to thermal expansion, and an optical disk including the laminate as a part of a layer structure.

[0002]

2. Description of the Related Art Optical disks having a phase change recording layer have already been manufactured or sold for recording digital signals. For example, a CD-RW (rewritable), a DVD (digital versatile disk) -RW, and a RAM (random access memory) correspond thereto. They generally have a film structure of a four-layer structure such as a plastic substrate / ZnS · SiO ₂ / chalcogen-based phase-change recording medium / ZnS · _SiO 2 / Al alloy. An optical disc having a phase change type recording layer performs recording by irradiating a crystal layer of a recording material with light to change a light irradiation part to an amorphous layer. Therefore, the recording layer must be a “crystal layer” in an initial state (a state where optical recording is possible). Since this recording layer is generally formed at a temperature of about 100 ° C. by sputtering or the like, it is an “amorphous layer” at the time of manufacture, and “initial crystallization” for crystallizing the entire recording layer is necessary. It is.

In the manufacturing process of an optical disk, the entire surface of the substrate is brought to a temperature of about 100 ° C. during the film formation by sputtering. The temperature rises. In the case of an optical disk using an inexpensive plastic substrate, the substrate is greatly warped due to the temperature difference between the front and back surfaces of the substrate during sputtering film formation and the high temperature treatment during the initial crystallization process in the phase change optical disk. In the case of a DVD-RW substrate having a high recording density, the thickness is 0.6 mm, which is half the thickness of a conventional CD-RW, which poses a more serious problem.

[0004] As a conventional technique for relieving residual stress due to thermal expansion, for example, Japanese Unexamined Patent Publication No. 07-240570 discloses a hybrid IC in which an alumina thin film is formed on a metal substrate as an intermediate layer. It is also disclosed that a thin film having a small coefficient of thermal expansion and a larger coefficient of thermal expansion than alumina is provided to prevent peeling of the alumina thin film. However, this technique is not applicable when the substrate is limited to a metal and the thin film is a ceramic material, and when the coefficient of thermal expansion of the substrate is smaller than the coefficient of thermal expansion of the thin film. In the field of optical discs, thermal expansion of the recording layer during phase change recording has been regarded as a problem, but no invention has been found that proposes a solution to the problem of residual stress after the manufacturing process that the present invention is trying to solve.
JP-A-5-3252 discloses a method for alleviating thermal expansion during recording.
No. 61 discloses that a thin film made of a metal material having a smaller coefficient of thermal expansion than the reflective layer is provided as an intermediate layer between the upper dielectric layer and the reflective layer. However, this method has the opposite effect if the coefficient of thermal expansion of the intermediate layer is even smaller than that of the upper dielectric layer.

[0005] In the first place, the warpage is caused by a difference in thermal expansion coefficient between the substrate and the functional thin film. Since there is a difference in thermal expansion coefficient between the two, a residual stress always occurs when the substrate is cooled from a high temperature to room temperature, and the substrate warps due to the stress. For example, in the case of mass-produced phase change optical disks, the cause of warpage is that the elongation of the polycarbonate substrate at a high temperature is greater than the elongation of the lower dielectric thin film.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a laminated body having a small residual stress due to thermal expansion and an optical disk using the laminated body.

[0007]

According to the present invention, a residual stress due to thermal expansion is provided between a substrate and a functional thin film (for example, a lower dielectric layer) by providing a stress relaxation layer having a thermal expansion coefficient intermediate between the two. Can be reduced. That is, the above problems are solved by the following inventions 1) to 7) (hereinafter, referred to as inventions 1 to 7). 1) A laminate having two or more functional thin films on a substrate, wherein the thermal expansion coefficient of the functional thin film (stress relaxation layer) in contact with the substrate is the same as the thermal expansion coefficient of the substrate and the stress relaxation layer. A laminate having an intermediate value of the coefficient of thermal expansion of a functional thin film to be subsequently laminated. 2) An optical disk including the laminate according to 1) as a part of a layer structure. 3) The functional thin film following the substrate and the stress relaxation layer is a lower dielectric layer, and further thereon a phase change recording layer / upper dielectric layer /
The optical disc according to 2), wherein the reflective heat dissipation layer is laminated. 4) The optical disc according to 3), wherein the lower dielectric layer also serves as a stress relaxation layer. 5) The optical disc according to 4), wherein the lower dielectric layer is composed of two layers, and a layer closer to the substrate also serves as a stress relaxation layer. 6) The stress relaxation layer or the portion also serving as the stress relaxation layer is made of Zn.
The optical disc according to any one of 3) to 5), wherein S and SiO ₂ are main components and at least one element selected from boron, phosphorus, and arsenic. 7) The optical disc according to 6), wherein the main component of the lower dielectric layer is also ZnS and SiO ₂ .

Hereinafter, the present invention will be described in detail. Book
In the invention, a transparent substrate is usually used. As an example of that material
Are polycarbonate, polymethyl methacrylate,
Examples include polyolefins and various glasses. Stress relaxation
The material of the layer includes the coefficient of thermal expansion of the substrate and the functional thin film (eg,
For example, the lower coefficient of thermal expansion of the lower dielectric layer)
You can choose from various things that you have. As an example
The MgF₂, PbS, TeO₂, TiO₂, Mg
O, In₂O ₃, TiN, CeO₂, ZnS, SiO₂
And the like. Among them, ZnS and SiO₂The main
And doped with elements such as boron, phosphorus and arsenic
Preferably, ZnS.SiO₂Some of the Si inside is ho
Replacement with elementary weakens the bond at that part
Then, ZnS · SiO of the lower dielectric layer₂Thermal expansion coefficient than
Can be increased. As the dope material,
Not only elements but also generally have higher electronegativity than Si
Material is more or less effective.
You.

As a material for the lower dielectric layer, for example, Zn
A metal sulfide such as S, SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ , ZnSe, a metal oxide, a metal nitride, a metal selenide, or a mixture thereof can be used. The recording layer is not particularly limited, but various alloys are preferably used. As a specific example, In-
Sb-Te, Ag-In-Sb-Te, Se-Sb-T
e, In-Se-Te, Sn-Se-Te, In-Sb
-Se, Bi-Sb-Se, Ge-Sb-Te, In-
Ge-Sb-Te, Pd-Ge-Sb-Te, Ni-G
e-Sb-Te, Co-Ge-Sb-Te, Ge-Te
-Bi, Ge-Te-Bi-Se, Ge-Te-Sn,
Ge-Te-Sn-Au may be mentioned, but Ag-In-Sb-Te suitable for high-density recording is particularly preferable because the erased portion is a crystal formed by melt recrystallization. It is preferable that the upper dielectric layer also functions as a protective layer, and the same material as that of the lower dielectric layer can be used. Al, Au, Ag,
Metals such as Cu and alloys thereof are preferably used, but are not particularly limited thereto. Further, if necessary, a protective layer may be provided on the reflective heat dissipation layer. As the material, an ultraviolet curable resin or the like is used.

[0010]

EXAMPLES The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 First, a polycarbonate substrate having a diameter of 120 cm and a thickness of 0.6 mm was prepared by injection molding. Next, the following layers were formed on this substrate by a sputtering apparatus whose top view was shown in FIG. The film formation in this case was performed using an apparatus having six chambers. However, the number of chambers is not limited to six, and production can be performed with four or more chambers. Next, the breakdown of the material of each layer in each film forming chamber is shown. Film forming chamber 1: ZnS · SiO ₂ (B, P, As doped)
(Stress relaxation layer) Film forming chamber 2: ZnS.SiO ₂ (lower dielectric layer) Film forming chamber 3: ZnS.SiO ₂ (lower dielectric layer) Film forming chamber 4: AgInSbTe (recording layer) Film forming chamber 5: ZnS.SiO ₂ (upper dielectric layer) Film forming chamber 6: Al (reflective heat dissipation layer) Next, sputtering conditions in each film forming chamber will be described. In the film forming chamber 1,
Under the following conditions, a ZnS.SiO ₂ (B-doped) film was formed by a sputtering method. Target material: SiO ₂ (19.5 mol%), ZnS
(79.5 mol%), B (1.0 mol%) Input power: RF 4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 90 nm In the film forming chamber 2 and the film forming chamber 3, the following conditions were satisfied. By ZnS ・ S
An iO ₂ film was formed. Target material: SiO ₂ (20.5 mol%), ZnS
(79.5 mol%) Input power: RF 4 kW / 8 inch target, gas pressure: 2 mTorr Gas type: Ar Film thickness: 50 nm In the film forming chamber 4, an AgInSbTe film was formed under the following conditions. Input power: DC 0.4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 20 nm In the film forming chamber 5, a ZnS.SiO ₂ film was formed under the following conditions. Input power: RF 4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 20 nm In the film forming chamber 6, an Al film was formed under the following conditions. Input power: DC 5 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 140 nm Finally, after applying an ultraviolet curable resin, a protective layer was formed by irradiating ultraviolet light to obtain an optical disk. The optical disk was irradiated with a laser beam focused at a size of 1 μm × 96 μm under the following conditions to crystallize the AgInSbTe recording layer. Crystallization conditions (rotational linear velocity: 4 m / s, laser feed rate:
50 μm / rotation, laser input power 800 mW)

Comparative Example 1 An optical disk according to the prior art was manufactured as follows. First, diameter 120cm, thickness 0.6m by injection molding
m of the polycarbonate substrate was formed. Next, a ZnS.SiO ₂ film was formed on the substrate in the film forming chambers 2 and 3 under the following conditions. Input power: RF 4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 63 nm In the film forming chamber 4, an AgInSbTe film was formed under the following conditions. Input power: DC 0.4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 20 nm In the film forming chamber 5, a ZnS.SiO ₂ film was formed under the following conditions. Input power: RF 4 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 20 nm In the film forming chamber 6, an Al film was formed under the following conditions. Input power: DC 5 kW / 8 inch target Gas pressure: 2 mTorr Gas type: Ar Film thickness: 140 nm Finally, after applying an ultraviolet curable resin, a protective layer was formed by irradiating ultraviolet light to obtain an optical disk. This optical disk was irradiated with a laser beam focused at a size of 1 μm × 96 μm under the following conditions to crystallize the AgInSbTe recording layer. Crystallization conditions (rotational linear velocity: 4 m / s,
(Laser feed speed: 50 μm / rotation, laser input power 800 mW)

In the stress relaxation layer of the first embodiment, ZnS.
SiO₂By replacing some of the Si inside with B
Since the coupling becomes weaker at the portion, the ZnS.S
iO ₂The thermal expansion coefficient becomes larger than that. That is, stress relaxation
The coefficient of thermal expansion of the layer is based on the polycarbonate substrate and the lower dielectric
The size between the layers. At this time, the material to be doped is B
Besides, the same effect can be obtained with P or As. Example 1
Of the 0.6 mm polycarbonate substrate in 1.
5 deg, and the warpage of Comparative Example 1 was 2.2 deg.
And B-doped ZnS / SiO₂In the comparative example 1
Is 2.2 deg and B-doped ZnS · SiO₂
Example 1 in which is provided as a stress relieving layer,
ZnS / SiO directly on the substrate₂From the comparative example
Is clearly superior. Here, "deg" refers to the figure
As shown in Fig. 2, when the recording medium is held horizontally,
Is the maximum value of the angle between the tangent and the horizontal.

[0014]

According to the first aspect of the present invention, a laminate having a small residual stress due to thermal expansion can be provided. Invention 2,
According to 3, an optical disk with small residual stress due to thermal expansion can be provided. According to the fourth aspect, since the lower dielectric layer is a stress relaxation layer, it is possible to provide an optical disk having small residual stress due to thermal expansion after a high-temperature process in manufacturing. According to the fifth aspect of the present invention, it is possible to provide an optical disk having small residual stress due to thermal expansion by including a stress relaxation portion in the dielectric layer. According to the present inventions 6 and 7, by replacing a part of the silicon atom with one of boron, phosphorus and arsenic, the bond of the part is weakened.
An optical disk with small residual stress due to thermal expansion can be provided.

[Brief description of the drawings]

FIG. 1 is a top view of a sputtering film forming apparatus.

FIG. 2 is a diagram for explaining “deg”.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H111 FA01 FA11 FA12 FA21 FB08 FB20 FB25 FB27 4K029 AA11 AA24 BA03 BA21 BA64 BB02 BD00 CA05 DC02 5D029 JA01 LA13 LA17 LB02 LB07 LB11 LC19 NA07 NA08 NA09

Claims (7)

[Claims] 1. A laminate having two or more functional thin films on a substrate, wherein a functional thin film (stress relaxation layer) in contact with the substrate has a coefficient of thermal expansion that is equal to the coefficient of thermal expansion of the substrate and the stress of the substrate. A laminate having an intermediate value of the coefficient of thermal expansion of a functional thin film laminated after the relaxation layer. 2. An optical disc comprising the laminate according to claim 1 as a part of a layer structure. 3. The functional thin film following the substrate and the stress relaxation layer is a lower dielectric layer, on which a phase-change recording layer / upper dielectric layer / reflective heat dissipation layer is laminated. optical disk. 4. The optical disk according to claim 3, wherein the lower dielectric layer also functions as a stress relaxation layer. 5. The optical disk according to claim 4, wherein the lower dielectric layer comprises two layers, and a layer closer to the substrate also serves as a stress relaxation layer. 6. A stress relaxation layer or a portion which also serves as a stress relaxation layer contains ZnS and SiO ₂ as main components, and contains boron, phosphorus,
4. The composition according to claim 3, comprising at least one element selected from arsenic.
6. The optical disc according to any one of claims 1 to 5, 7. The lower dielectric layer is mainly composed of ZnS and Si.
O ₂ The optical disc of claim 6, wherein.