JPS62139156A - Optical recording device - Google Patents

Abstract

PURPOSE:To obtain the titled optical recording device having plural antireflection layers capable of accomplishing sufficient antireflection functions by providing the plural antireflection layers between a recording medium and a substrate. CONSTITUTION:The plastic substrate is formed with glass, polycarbonate, acrylic resin, epoxy resin, etc. A silicon nitride film 2 having 2.3 refractive index and 850Kt thickness, a silicon nitride film 3 having 2.0 refractive index and 970Kt thickness, a silicon nitride film 4 having 2.3 refractive index and 650Kt thickness, a TbFeCo amorphous alloy film 5 having 1,000Kt thickness, and a silicon nitride film 6 having 2.0 refractive index and 500Kt thickness are formed on the substrate 1. The silicon nitride film having 2.3 refractive index and that having 2.0 refractive index can be formed by respectively setting the partial pressures of nitrogen to 3.75X10<-4>Torr and 1.5X10<-3>Torr. Consequently, plural dielectric films, namely the antireflection layers, having different refractive indexes and contg. no oxygen can be formed, and the reproducing performance and reliability of the optical recording device can be remarkably improved.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is an optical recording device that reads information using light. The present invention relates to an optical recording device that reads information using light.

<Conventional technology> Conventionally, rare earth transition metal alloys (TbFe, GdTbFe.

In magneto-optical recording using recording media such as TbFeCo, TI+Co, 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, 5i02 and A
Efforts have been made to form a nitride such as IN or 5ishL, a sulfide such as ZnS, or a fluoride such as MgF on a recording medium to serve 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 a recording method in which the above dielectric layer is formed on the recording medium, the ratio of reflectance between the amorphous part and the upper part of the crystal f is small and the S/N ratio is poor. Efforts have been made to increase the reflectance ratio as an antireflection layer in the amorphous portion and to increase the S/N 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 used as a perfect anti-reflection layer and has 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,
An example in which the Kerr rotation angle was sufficiently increased has been reported (Y
, To+n1ta, T, Yoshino.

J, Opt, Soc, A+n, Vol, 1, No,
8. (1984), 809).

However, when laminating the above-mentioned antireflection layer, at least two types of dielectric materials with different refractive indexes are required, and it is difficult to form dielectric materials with different refractive indexes with excellent reliability. When using this method, an apparatus equipped with multiple evaporation sources and targets is required, leading to an increase in the size and cost of the apparatus, making it unsuitable for practical use.

In addition, since silicon nitride film is a dense nitride film that does not contain oxygen, it has been reported that it is an excellent film as a protective film to prevent oxidation of magneto-optical recording media (Arisui, Maeda et al. , IEEJ Study Group Material MA G-85-81 (19
85) l.

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 with the aim 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 object described in item 1, the optical recording device of the present invention is provided with a plurality of antireflection layers between the recording medium and the substrate.

<Example> Hereinafter, a detailed explanation will be given based on an illustrated embodiment.

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 (101ycarbonaLe; PC) or acrylic acid resin (for example, methyl methacrylate polymer). Union (Iol
ymethyl metl+acrylate;PMM
A)), a substrate such as an epoxy resin or other plastic substrate, 2 is a silicon nitride film with a refractive index of 23 and a film thickness of 850 [in], and 3 is a silicon nitride film with a refractive index of 2.0 and a film thickness of 970 [in]. Film 4 is a silicon nitride film with a refractive index of 2.3 and a thickness of 650.
The amorphous alloy film 6 is a silicon nitride film with a refractive index of 2.0 and a thickness of 500 U.

Here, the silicon nitride 2.3.4.6 is formed by =4- sputtering in a nitrogen atmosphere using a silicon (Si) target. 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,
Incident power 1 [ku+], reaction chamber gas pressure 2 6 [m
When reactive sputtering was performed by varying the nitrogen partial pressure while maintaining the silicon nitride film at a constant pressure of 1.5 Torr, the results 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 irradiated with a laser beam with a wavelength of 780 [nm], and the nitrogen partial pressure is 3
Torr] or less, light absorption appeared for laser light with a wavelength of 780 [nm]. Here, the material that can be used as the antireflection layer of the optical recording device needs to be transparent to the light used for recording and reading information. On the other hand, considering a transparent film, as can be seen from Figure 2, by setting the nitrogen partial pressure to 3.75X10-' [Torr] and 1.5X10-' [Torr],
Silicon nitride films with refractive indexes of 2.3 and 2.0 can be created.

As in the above embodiment, when the antireflection layer is formed by reactive sputtering using a Si target, only one target is required to form two types of silicon nitride films with different refractive indexes, that is, dielectric layers. This prevents the sputtering equipment from increasing in size and reduces costs, and compared to using the sintered body of nitrous hydricone Targetera 1, there is no risk of oxygen being taken in, making it more reliable as a protective film. It has the advantage that a high silicon nitride film can be formed.

In this example, TbF (IC) is used as the recording medium.
o Although an amorphous alloy film was used, transfer metal alloys (TbFe, GdTl) Fe, TbCo, GdTbCo with other rare earth 3
etc.) and recording media that perform recording and reproduction using reflectance changes (TeGe, AsTeGe, 5nTeSe, TeO
x, etc.), and the silicon nitride film may be formed using other methods such as vapor deposition. Furthermore, the film thickness, refractive index, formation conditions, etc. of each film of the optical recording device of the present invention are not limited to those shown in the above embodiments, and as shown in FIG. By having a configuration like the optical recording device of the invention, it is possible to form a plurality of oxygen-free dielectric films, that is, antireflection layers with different refractive indexes, using a single target laser or vapor deposition source. Therefore, a significant improvement in the reproduction performance and reliability of optical recording devices can be expected.

[Brief explanation of drawings]

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-TbPeCo amorphous metal amorphous deposited film Sharp Corporation

Claims (4)

[Claims] (1) In an optical recording device that includes a recording medium on which information is recorded by irradiation with a predetermined amount or more of recording radiant energy on a predetermined substrate, a plurality of antireflection layers are provided between the recording medium and the substrate. An optical recording device characterized by: (2) The optical recording device according to claim 1, wherein the antireflection layer is formed of Si nitride. (3) In an atmosphere of N_2 or A with Si as a target
2. The optical recording device according to claim 1, wherein the antireflection layer is formed of Si nitride prepared by reactive sputtering in an atmosphere of a mixed gas of r and N_2. (4) The optical thickness of each anti-reflection layer is set to 1/4 of the wavelength of the readout light, and the anti-reflection layer is formed by two or more layers having different refractive indexes. 1
The optical recording device according to items 1 to 3.