JPH02226528A - Optical disk - Google Patents

Abstract

PURPOSE:To reduce noise in a regenerated signal by providing a mixed dielectric film having almost the same refractive index as that of a substrate on the substrate, and forming a prescribed irregular pattern on the film. CONSTITUTION:A mixed transparent dielectric film 2 having almost the same refractive index as that of a glass substrate 1 is formed on the substrate 1. Next, a pattern corresponding to encoded recording information is formed on the film 2. Next, a reflection film 3 is formed on the pattern, and a protection film 4 is provided on the film 3. Thereby, the double refraction of a readout laser beam generated by difference between the substrate 1 and the film 2 can be eliminated, and the noise in the regenerated signal can be reduced.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an optical disc.

(Prior Art) As an optical disk in which a transparent dielectric film is formed on a conventional glass substrate, and bits consisting of a concavo-convex pattern corresponding to recorded information encoded on the transparent dielectric film are formed, for example, There is a structure disclosed in Japanese Patent No. 59-210547, and the structure is as shown in FIG. That is, a silicon oxide film 9 is provided on a glass substrate 1, a concavo-convex pattern for an optical memory element is provided on the silicon oxide film 9, and an optical memory medium 8 (reflective film for compact discs, etc.) is provided on the upper surface. It has a structure in which the upper surface is covered with a protective film.

Next, the manufacturing method will be explained with reference to the drawings. Note that FIGS. 4(a) to 4(d) are radial cross-sectional views of the optical disk shown in the order of steps.

First, as shown in FIG. 4(a), a silicon oxide film 9 is formed on a glass substrate 1, a photoresist film 5 is applied on the silicon oxide film 9, and the photoresist film 5 is exposed and developed. Pattern lines or discontinuous lines with the same width as the grooves for the optical memory element.

Next, as shown in Figure 4(b), CF, CHF3
Etching is performed in a reactive gas plasma 6 such as the like to form uneven grooves on the silicon oxide film 9.

Next, as shown in FIG. 4(e), the photoresist film 5 is coated with a solvent such as acetone or oxygen gas plasma 7.
The silicon oxide film 9 is removed by sputtering to leave a groove on the silicon oxide film 9.

Next, as shown in FIG. 4(d), an optical memory medium 8 is formed on the silicon oxide film 9 in which the grooves have been formed, and its upper surface is covered with a protective film 4 to form an optical disk. Instead of the optical memory medium 8, a reflective film may be formed on a compact disk or the like.

(Problems to be Solved by the Invention) In the conventional optical disc described above, a silicon oxide film is formed on a glass substrate. This structure prevents the alkali metal in the glass from diffusing into the reflective film or optical memory medium and suppresses the resulting corrosion, so it is an effective structure for increasing the long-term reliability of the optical disk. However, research by the present inventors has revealed that when actually reading information from an optical disk, there is a problem in that noise in the reproduced signal becomes extremely large due to birefringence of the read laser beam. This is the above-mentioned known example (Japanese Unexamined Patent Publication No. 5
The same results were obtained when other dielectric films (for example, Si3N4, AIN, and MgF films) described in Japanese Patent No. 9-210547 were used.

The object of the present invention is caused by the difference in refractive index between a transparent substrate and a transparent dielectric film. An object of the present invention is to provide an optical disc that can eliminate birefringence of a read laser beam and reduce noise in a reproduced signal.

(Means for Solving the Problems) The optical disc of the present invention has a mixed transparent dielectric film on a substrate having approximately the same refractive index as the substrate, and encoded recording information is provided on the mixed transparent film. It has a structure in which a corresponding pattern or a pattern for recording information is formed, a reflective film or an optical memory medium is provided on the pattern, and a protective film is provided on the reflective film or the optical memory medium. There is. Here, as the transparent dielectric film, titanium oxide, aluminum oxide, titanium nitride, silicon nitride, magnesium oxide, tin oxide, lanthanum oxide, indium oxide, zirconium oxide, bismuth oxide, or A mixed transparent dielectric film formed by mixing silicon oxide with at least one of cerium or antimony oxide can also be used.

(Function) In the optical disk having the structure of the present invention, since there is no difference in refractive index between the substrate material and the mixed transparent dielectric film formed on the upper surface thereof, birefringence of the read laser beam due to the difference in refractive index is reduced. This is less likely to occur, and the noise in the reproduced signal is reduced compared to conventional products.

(Example) Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a radial cross-sectional view of an embodiment of an optical disc according to the invention. The optical disc according to the present invention has a thickness of 1.
A width of 0.5 pm and a length of 0.5 pm are formed on the top surface of a 2 mm glass substrate 1.
It has a mixed transparent dielectric film 2 with a thickness of 0.3 μm made of silicon oxide and titanium oxide and has a pattern of predetermined encoded recording information of 9 to 3.3 pm and a depth of 0.11 pm. It has a structure in which it has a reflective film 3 with a thickness of 0.15 pm, and its upper surface is covered with a protective film 4 with a thickness of 2 pm.

Hereinafter, the above-described optical disc according to the present invention will be explained in more detail using FIGS. 2(a) to (D).
) to (0 are radial cross-sectional views of an optical disk shown in the order of steps for detailed explanation of the present invention.

First, as shown in FIG. 2(a), a mixed transparent dielectric film 2 made of silicon oxide and titanium oxide is placed on a glass substrate 1.
A film with a thickness of 0.3 pm is formed. At that time, mixed transparent dielectric film 2
By changing the mixing ratio of silicon oxide and titanium oxide therein, the refractive index of the formed mixed transparent dielectric film 2 was adjusted to be approximately the same as the refractive index of the glass substrate. The refractive index of the glass substrate in this example is 1.6 at a wavelength of 0.5911 m, and the refractive index of silicon oxide and titanium oxide is
31 Committee, “Thin Film Handbook”, Ohmsha, 19
As disclosed in 1983, page 824, wavelength 0.5
At 5 pm, they are 1.45 and 2.0-2.7, respectively. To form the mixed transparent dielectric film 2, a co-evaporation method is performed using an electron beam evaporation apparatus capable of simultaneously irradiating silicon oxide and titanium oxide with two electron beams. The deposition conditions were an ultimate vacuum of 3 x 10 Pa, and an emission charge for silicon oxide! 80mA, emission current for titanium oxide 30mA, substrate temperature during deposition 70°C
It is. As a result of film formation, the weight ratio of silicon oxide and titanium oxide is approximately 7=3, and the refractive index of the film is 1.
．． It is 59.

In addition, when performing the co-sputtering method, the argon pressure is 0.
．． Titanium oxide is placed on the silicon oxide target at 4 Pa. At this time, the area ratio of the silicon oxide exposed part and the titanium oxide installed part is set to 7=3. The mixed transparent dielectric film produced has approximately the same refractive index and composition ratio as that obtained by co-evaporation.

Next, as shown in FIG. 2(b), the mixed transparent dielectric film 2
On top of this, a photoresist (based on novolak resin) is applied.
For example, a photoresist film made by diluting AZ1350 (manufactured by Hoechst Co., Ltd.) with thinner is coated to a thickness of 0.1 to 0.2 μm, and this is exposed and developed to produce a photoresist film having a pattern corresponding to the encoded information to be recorded. A film 5 is formed.

Next, as shown in FIG. 2C, reactive ion etching is performed using plasma 6 of reactive gas to etch the mixed transparent dielectric film 2 to a predetermined depth. When using CF as the reactive gas, the etching conditions are as follows: CF
4 gas pressure was 4.5 Pa, and input power was 100 W.

Next, as shown in FIG. 2(d), oxygen gas plasma 7
The photoresist film 5 is incinerated and peeled off using the following method.

Ashing conditions are oxygen gas pressure 4.0 Pa, input power 100
It is W.

Next, as shown in FIG. 2(e), a reflective film 3 made of aluminum is formed to a thickness of 0.1511 m. Electron beam evaporation was used to form the aluminum film, and the evaporation conditions were an ultimate vacuum of 3 x 10 Pa and an emission current of 8.
5 mA, and the substrate temperature during vapor deposition was 70°C.

Next, as shown in FIG. A sputtering method was used to form the protective film 4, and the conditions were an argon pressure of 0.5 Pa and an input power of 400 W.

According to research conducted by the present inventor, the noise of optical discs manufactured using the above-mentioned procedure of the present invention is reduced by approximately 5 dB compared to optical discs manufactured using conventional techniques, demonstrating the effectiveness of the present invention. Ta.

In this embodiment, an example was described in which a glass substrate was used as the substrate, but in that case, the composition of the glass is arbitrary, and any transparent glass substrate may be used. It is also possible to use a silicon oxide substrate. Furthermore, it is also possible to use a transparent resin substrate as the substrate. In that case, it is desirable to apply the present invention after coating the entire surface of the transparent resin substrate with a mixed transparent dielectric film having the same composition as the mixed transparent dielectric film 2. However, no matter which substrate is used, the composition of the mixed transparent dielectric film 2 must be determined to be approximately equal to the refractive index of the substrate used. Using various transparent substrates,
The mixing weight ratio when silicon oxide and titanium oxide are used as raw materials for the mixed transparent dielectric film 2 is shown in a table.

・Reinforced glass substrate ・Resin substrate Also, in this example, an example was described in which silicon oxide and titanium oxide were used as the composition of the mixed transparent dielectric film 2 having almost the same refractive index as the glass substrate 1, but other dielectrics other than these were described. (for example, at least one of aluminum, tantalum oxide, silicon nitride, aluminum nitride, magnesium oxide, tin oxide, lanthanum oxide, indium oxide, zirconium oxide, bismuth oxide, cerium oxide, and antimony oxide) and silicon oxide. You may. The mixing weight ratio when silicon nitride (having a refractive index of 1.85) is used as the dielectric material to be mixed is shown in a table.

Further, the weight ratio of silicon oxide and titanium oxide in this example is not limited to this value since the refractive index may change depending on the film forming conditions and film forming method. The same applies when silicon oxide and silicon nitride are used. In the above example,
Although silicon oxide and one type of dielectric are mixed, it is also effective to mix two or more types. Furthermore, although CF was used as the reactive gas of the reactive gas plasma 6 in this example, CHF3, SF6, CI□, CCl4, CO,
CO2 or the like may also be used. Further, in this embodiment, an example was described in which aluminum was used as the reflective film 3, but other materials with high reflectance (for example, steel, stainless steel, nickel, titanium nitride, etc.) may be used. Furthermore, an optical memory medium may be formed on the mixed transparent dielectric film 2 to record and reproduce information using the magneto-optic effect, or to record and reproduce information by utilizing the phase change of the material. The structure of the optical disc of the present invention, which reduces noise, is effective.

(Effects of the Invention) As described above, according to the optical disk configuration of the present invention, a predetermined uneven pattern is formed on a mixed transparent dielectric film having a refractive index almost equal to that of the substrate, so that it is possible to form a predetermined uneven pattern using a conventional manufacturing method. An optical disc can be realized in which the noise in the reproduced signal is greatly reduced without sacrificing the advantage of preventing the diffusion of alkali metals.

[Brief explanation of the drawing]

FIG. 1 is a radial cross-sectional view of an optical disc for explaining the structure of the optical disc of the present invention. FIGS. 2(a) to (0) are radial cross-sectional views of an optical disc shown in the order of steps to explain the present invention in detail. FIG. 3 is a diagram illustrating the structure of an optical disc according to a conventional technique. Fig. 4(a) to (d) are new views of the optical disc in the radial direction shown in the order of steps for explaining the conventional optical disc manufacturing method. In the figure, 1... Glass substrate, 2... Mixed transparent dielectric film, 3... Reflective film, 4... Protective film, 5... Photoresist film, 6... Reactive gas plasma. , 7... Oxygen gas plasma, 8... Optical memory medium, 9... Silicon oxide film.

Claims (2)

[Claims] (1) A mixed transparent dielectric film having approximately the same refractive index as the substrate is provided on the substrate, and a pattern corresponding to encoded recording information or a pattern for information recording is formed on the mixed transparent dielectric film. What is claimed is: 1. An optical disc comprising: a reflective film or an optical memory medium on the pattern; and a protective film on the reflective film or the optical memory medium. (2) The mixed transparent dielectric film described in claim (1) may be made of titanium oxide, aluminum oxide, titanium nitride, silicon nitride, magnesium oxide, tin oxide, lanthanum oxide, or An optical disk using a mixed transparent dielectric film formed by mixing at least one of indium, zirconium oxide, bismuth oxide, cerium oxide, or antimony oxide with silicon oxide.