JPH0518187B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is an optical recording device that reads information using light, in which information is recorded by causing some kind of change in the recording medium. , relates to a method of manufacturing an optical recording device that reads information using reflected light.

<Conventional technology> Conventionally, rare earth transition metal alloys (TbFe, GdTbFe,
In magneto-optical recording using recording media of TbFeCo, TbCo, GdTbCo, GdCo, etc., it has been difficult to increase the signal-to-noise ratio (S/N ratio) because the Kerr rotation angle is small. For this reason, oxides such as SiO and SiO ₂
AlN, nitride of Si ₃ N ₄ , sulfide such as ZnS, or
Efforts have been made to form a fluoride such as MgF ₂ on the recording medium as an antireflection layer to increase the Kerr rotation angle and improve reproduction performance.

In addition, by irradiating an amorphous semiconductor such as As-Te-Ge with laser light and crystallizing the irradiated part of the amorphous semiconductor, the difference in reflectance between the amorphous part and the crystallized part is utilized. Even in the case of the recording method, the ratio of the reflectance between the amorphous part and the crystallized part is small, and the S/
Since the N ratio is poor, efforts have been made to increase the S/N ratio by forming the above-mentioned dielectric layer on the recording medium and using it as an antireflection layer for the amorphous portion to increase the reflectance ratio.

<Problems to be Solved by the Invention> However, the refractive index of the dielectric layer that is actually formed takes a value specific to the substance, so it cannot be a perfect anti-reflection layer and cannot provide sufficient contrast. It was difficult to increase it.

Therefore, the antireflection function is enhanced by laminating multiple antireflection layers whose optical thickness is 1/4 of the wavelength of the readout light on the recording medium, for example.
In the case of magneto-optical recording, examples of sufficiently increasing the Kerr rotation angle have been reported {Y. Tomita, T. Yoshino,
J.Opt.Soc.Am.Vol.1, No.8, (1984), 809}.

However, when laminating the above-mentioned antireflection layer, at least two types of dielectric layers with different refractive indexes are required, and it is difficult to form dielectric layers with different refractive indexes with excellent reliability, as well as vacuum evaporation method. When the sputtering method is used, an apparatus equipped with multiple deposition sources and targets is required, which leads to an increase in the size and cost of the apparatus and is not suitable for practical use.

In addition, silicon nitride film is a dense nitride film that does not contain oxygen, so it has been reported that it is an excellent protective film for preventing oxidation of magneto-optical recording media {Arimune, Maeda et al. , Institute of Electrical Engineers of Japan study group materials
MAG-85-81 (1985)}.

However, when forming a silicon nitride film by sputtering, the conventional method of using a sintered body of silicon nitride as a target has the problem that oxygen contained in the sintered body target is released during sputtering and oxidizes the recording medium. There was a problem that it was not very desirable.

The present invention has been made in view of these points, and has been made for the purpose of providing an optical recording device in which a plurality of antireflection layers are formed that can sufficiently perform an antireflection function.

<Means for Solving the Problems> In order to achieve the above object, the present invention performs sputtering using a silicon target in a nitrogen atmosphere and changes the nitrogen partial pressure at the time. We decided to adjust the refractive index of the antireflection layer.

<Example> Hereinafter, a detailed description will be given based on an example shown in the drawings.

FIG. 1 shows the structure of an embodiment of the optical recording device of the present invention, in which 1 is made of glass or polycarbonate polymer (PC).
or acrylic acid resin {for example , methyl methacrylate polymer ( polymethylmethacrylate ;
PMMA)}, substrate such as epoxy resin or other plastic substrate, 2 has a refractive index of 2.3 and a film thickness of 850 [Å]
Silicon nitride film 3 has a refractive index of 2.0 and a film thickness of 970.
[Å] silicon nitride film, 4 has a refractive index of 2.3 and a film thickness
650 [Å] silicon nitride film, 5 is film thickness 1000 [Å]
The TbFeCo amorphous alloy film 6 is a silicon nitride film with a refractive index of 2.0 and a thickness of 500 [Å].

Here, the silicon nitride 2, 3, 4, 6 is
It is formed by sputtering using a silicon (Si) target in a nitrogen atmosphere. At this time, the refractive index of the silicon nitride film is changed by changing the nitrogen partial pressure during sputtering. For example, in a high-frequency bipolar magnetron sputtering device using a Si target, in an argon and nitrogen atmosphere, the nitrogen partial pressure is varied while maintaining the incident power at 1 [kW] and the gas pressure in the reaction chamber at 6 [mTorr]. When reactive sputtering was performed, results as shown in FIG. 2 were obtained regarding the real part of the refractive index of the silicon nitride film. However, the refractive index is the value when laser light with a wavelength of 780 [nm] is irradiated, and when the nitrogen partial pressure is 3 × 10 ^-4 [Torr] or less, the refractive index is the value when laser light with a wavelength of 780 [nm] is applied. Absorption appeared. Here, the material that can be used as the antireflection layer of an optical recording device must be transparent to the light used for recording and reading information. On the other hand, if we consider a transparent membrane, the nitrogen partial pressure is 3.75×10 -4 [Torr] and 3.75×10 ^-4 [Torr] and
By setting 1.5×10 ^-3 [Torr], the refractive index
2.3 and 2.0 silicon nitride films can be formed.

When the antireflection layer is formed by reactive sputtering using a Si target as in the above embodiment, only one target is required to form two types of silicon nitride films with different refractive indexes, that is, dielectric layers. The silicon nitride film is highly reliable as a protective film because it prevents the sputtering equipment from becoming larger and reduces costs, and there is no risk of oxygen being taken in compared to using a sintered silicon nitride target. It has the advantage of being able to form

In this example, as a recording medium,
Although TbFeCo amorphous alloy film was used, other rare earth transition metal alloys (TbFe, GdTbFe, TbCo, GdTbCo)
etc.) and recording media that perform recording and playback using changes in reflectance (TeGe, AsTeGe, SnTeSe, TeOx)
etc.) is also applicable. Furthermore, the film thickness, refractive index, formation conditions, etc. of each film of the optical recording device of the present invention are as follows:
It is not limited to those shown in the above embodiments, and may be selected as appropriate.

<Effects of the Invention> As described above, in the method for manufacturing an optical recording device of the present invention, a dielectric layer made of nitride having an optimal refractive index can be easily formed using a single target. Furthermore, it becomes possible to form a plurality of oxygen-free dielectric films having different refractive indexes, that is, antireflection layers, and a significant improvement in the reproduction performance and reliability of optical recording devices can be expected.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing the structure of an embodiment of the optical recording device of the present invention, and FIG. It is a figure showing the relationship with partial pressure. 1... Glass substrate, 2, 3, 4, 6... Silicon nitride film, 5... TbFeCo amorphous alloy film.

Claims (1)

[Claims] 1. In a method for manufacturing an optical recording device comprising a substrate, a dielectric layer made of nitride, and a recording medium layer, when forming the dielectric layer made of nitride by sputtering, nitrogen content during sputtering is A method for manufacturing an optical recording device, characterized in that the refractive index of the dielectric layer made of nitride is adjusted by changing the pressure.