JPH073707B2 - Magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a magneto-optical recording medium, particularly excellent in chemical stability, a large Kerr rotation angle, and excellent light transmittance.
The C / N ratio is also good, and the present invention relates to a magneto-optical recording medium capable of improving the recording density.

[Prior Art] In recent years, rewritable magneto-optical memory has attracted attention as the information-oriented society advances, and rare earth element-transition metal element film such as TbFeCo is used as a magnetic film for the magneto-optical memory. However, this has the disadvantage that the C / N of the reproduced signal is not sufficient because the Kerr rotation angle obtained is not so large.

[Problems to be Solved by the Invention] Therefore, in this type of magneto-optical recording medium, a dielectric layer (film) such as SiO, SiN, or AlN is formed on the surface of a conventionally known amorphous magnetic film, and By increasing the film thickness to λ / 4n (where λ is the laser wavelength and n is the refractive index), the apparent Kerr rotation angle is increased and C / N is increased (enhancement effect). The improvement of the characteristics is still insufficient, and the dielectric layer is required to have a higher refractive index and good transparency.

Further, the amorphous magnetic film used here contains a rare earth metal. However, since this rare earth metal is extremely easily oxidized, it has a magnetic property easily under high temperature and high humidity. There is a problem that it deteriorates, and there is a proposal that the above dielectric layer plays a role as a protective film.
In the case of oxides such as, on the contrary, the effect is not sufficient because the rare earth element causes an oxidation reaction with O in SiO, and nitrides such as SiN and AlN have such a small reactivity. Although it is suitable for the purpose of improving the corrosion resistance, it has a problem in mechanical strength because cracks easily occur when a film is formed on a resin substrate or the like.

It is also proposed to use BN for this dielectric film [M.Asano et al, IEEE.Trans.Magn.MAG-23,2
620, (1987)], which has a large refractive index, is transparent, and has excellent characteristics as a dielectric film, but it must be formed in a completely amorphous state even if it is formed by sputtering. However, the composition is non-uniform and unevenness occurs on the surface, which is problematic in terms of durability.

[Means for Solving the Problems] The present invention relates to a magneto-optical recording medium capable of solving the above problems, which includes a dielectric layer and a magnetic film on a transparent substrate placed on the light incident side. In a magneto-optical recording medium provided with a reflective film, the dielectric layer is made of an amorphous material made of BN containing H.

That is, the present inventors have conducted various studies to develop a magneto-optical recording medium having a large Kerr rotation angle, excellent light transmittance, good C / N, and improved recording density. When the body layer is made of an amorphous material made of BN containing H (hereinafter abbreviated as amorphous BN: H film material), 1) this film material contains H. Compared to the conventionally used SiO, SiN, AlN, etc., which have a refractive index of 1.4 to 1.8, this amorphous film is more likely to become amorphous and has a uniform composition and a smooth surface The BN: H film has a refractive index of 1.75 to 2.
Since it is 15, it has a great enhancement effect,
It also has a high light-transmitting property and has a very high light-transmitting property especially in the visible to infrared region, which gives a magneto-optical recording medium with a large C / N. 3) The amorphous BN: H film has a low thermal conductivity. Since the thermal diffusion of the laser irradiating the surface is small and the spread of the recording bit diameter can be suppressed, it is possible to improve the recording density. 4) In terms of durability and mechanical strength compared to conventional protective films Since it is excellent, it was found that the effect of protecting the magnetic film can be obtained, and the present invention was completed by conducting research on the method of forming this amorphous BN: H film.

This will be described in more detail below.

[Operation] The magneto-optical recording medium of the present invention has an amorphous BN: H film as the dielectric layer in the magneto-optical recording medium in which the dielectric layer, the magnetic film and the reflective film are provided on the transparent substrate.

The structure of this magneto-optical recording medium is known, and as shown in FIG. 1, for example, it is made of glass, quartz glass, polycarbonate resin, polymethylmethacrylate resin, etc. on which tracking guide groups are formed. A dielectric film 2, a magnetic film 3, a dielectric film 4 of the same quality as the dielectric film 2 and a reflective film 5 are sequentially laminated on a substrate 1, which is a transparent substrate as shown in FIG. 7 may have a three-layer structure in which a dielectric film 8, a magnetic film 9, and a dielectric film 10 are sequentially laminated on the transparent substrate 1, 7 from the light incident side of the transparent substrate 1, 7. When 11 is incident, the light 6 is reflected by the reflective film 5, and in the case of FIG. 2 in which the thickness of the magnetic film is thick, the incident light 11 is reflected by the magnetic film 9.

In the magneto-optical recording medium of the present invention, the dielectric films 2, 8 and / or
Alternatively, 4,10 are formed by the above-mentioned amorphous BN: H film, but this dielectric film is formed by boron trichloride (BC
l ₃ ), boron halides such as boron trifluoride (BF ₃ ) and boron hydrides such as diborane (B ₂ H ₆ ), and ammonia (NH ₃ ) and amines, etc. A nitrogen source composed of a nitrogen-containing gas such as that described above may be introduced into the reaction apparatus and a chemical vapor deposition method (hereinafter abbreviated as a CVD method) may be used.
For this CVD method, introducing a reaction gas into the vacuum device,
The plasma CVD method, in which plasma is excited and decomposed to form a film on the substrate, enables film formation even at a low temperature of 400 ° C or less, which is advantageous in the case of a resin substrate where heat resistance is a problem. Is given. In this case, when neither the boron source nor the nitrogen source described above has hydrogen atoms, it is necessary to use H ₂ gas or hydrogen-containing gas as the fourth component, but the availability of raw material gas It is preferable to use B ₂ H ₆ and NH _{3 as the} raw material gas from the viewpoint of easy handling.

The formation of this dielectric film can also be performed by a sputtering method. In this case, BN or B is used as a target, and the inside of the vacuum apparatus is set to a mixed gas atmosphere such as Ar-H ₂ or Ar-H ₂ -N _2. A high frequency may be applied to this to form a dielectric film on the substrate by reactive sputtering.

The dielectric film thus obtained is made of amorphous BN and H and has a thickness of 500 to 1,000 Å, but the composition ratio of each element is not particularly limited. However, this one has a refractive index
If it is less than 1.75, the apparent increase of θ _K (enhancing effect) due to the multiple reflection of light on the medium surface cannot be expected, and conversely 2.
If you try to make it larger than 15, the film quality deteriorates and the mechanical strength and durability are adversely affected, so the refractive index (n) is 1.
It is desirable that the composition is 75 to 2.15, but this composition is preferably such that the weight ratio is such that the nitrogen element is 10 to 30 and the hydrogen atom is 5 to 15 with respect to 100 boron element. The composition ratio of each element may be adjusted according to the film forming conditions to form a film.

In the magneto-optical recording medium of the present invention, a magnetic film and a reflective film are formed on this dielectric layer formed on a substrate. These may be known ones. Comprising a rare earth-transition metal element film, therefore
Consisting of rare earth elements such as Tb, Dy, Gd, Nd and transition metal elements such as Fe, Co, Ni, for example TbFe, TbFeCo, GdTbFe, GdDyFeCo
Amorphous metal film consisting of
0-500Å, in the case of the structure shown in FIG. 2, it may be formed by a sputtering method with a thickness of about 800-1,000Å. This reflective layer is a metal film of Al, Cu, Au, Ag, etc. with a thickness of 200-1,000. It should be set at about Å.

[Examples] Next, examples and comparative examples of the present invention will be described.

Examples 1 to 4 and Comparative Examples 1 to 2 A glass substrate was set in a plasma CVD apparatus and heated to 100 ° C., and B ₂ H ₆ and NH ₃ gases having a molar ratio shown in Table 1 were introduced into the apparatus. Then, the pressure inside the device was maintained at 2.5 Torr and a high frequency of 200 W was applied to the amorphous BN:
The H film was formed, the composition ratio of B and N of this film was measured by ESCA and AES, the analysis of H was measured by RBS and HFS, and the refractive index and transmittance of this film were measured. The result as shown in was obtained (Examples 1 to 3).

In addition, this amorphous BN: H film was formed by a sputtering method, put a glass substrate and BN as a target in a vacuum device, Ar gas 80% in the device,
A mixed gas atmosphere consisting of 5% H ₂ gas and 15% N ₂ gas,
Amorphous on the substrate by sputtering by applying a high frequency of 300 W with a pressure of 10 × 10 ^-3 Torr.
When a BN: H film was formed and the composition, refractive index and transmittance of this film were examined, the results as shown in Table 1 were obtained (Example 4), but this sputtering method was used for comparison. When a BN or SiO film containing no H was prepared, the refractive index and transmittance of the obtained dielectric film were inferior to those of Example 4 as shown in Table 1.

Next, Ar was formed on the amorphous BN: H film obtained in Example 1.
A 200 Å thick TbFe magnetic film is formed under the conditions of gas pressure of 7 × 10 ^-3 Torr and high frequency output of 300 W, and an amorphous BN: H film is formed on the TbFe magnetic film by the same plasma CVD method as above. A 400 Å-thick aluminum reflective film was formed by the sputtering method under the same conditions as the magnetic film formation described above to create a magneto-optical recording medium, and the Kerr rotation for a laser with a wavelength of 633 nm when the thickness of this dielectric film was changed When the change in the angle was examined, the results shown in Fig. 3 were obtained, and in order to examine the durability of this product, 85 ° C, 85% R
When the relationship between the holding time and the coercive force under the condition of H was investigated, the results shown in FIG. 4 were obtained.

For the sake of comparison, when this dielectric layer was formed of BN or SiO containing no H, the results as shown in FIGS. 3 and 4 were obtained. In Example 1, the film thickness d is d = λ / 4n 8
It has been shown that θ _K has a maximum value of 2.0 at around 0 nm, so that it has a sufficient enhancement effect. However, BN and SiO are inferior to this, and in Example 1, the coercive force is almost constant even after 500 hours. It was confirmed that this did not decrease much, whereas that of BN and SiO decreased considerably.

[Effects of the Invention] The present invention relates to a magneto-optical recording medium, which is a magneto-optical recording medium having a substrate provided with a dielectric film, a magnetic film and a reflective film as described above. According to this, since this dielectric film has a refractive index of 1.75 to 2.15, it has a large enhancing effect, and the Kerr rotation angle can be increased. Has excellent transparency, so that C / N is increased, and since this amorphous film contains H, the film surface becomes smooth and the thermal conductivity is low, so the thermal diffusion of the laser is small. As a result, the expansion of the diameter of the recording bit is suppressed, so that there is an advantage that the recording density is improved.

[Brief description of drawings]

1 and 2 are configuration diagrams of a magneto-optical recording medium, FIG. 3 is a relationship graph between the Kerr rotation angle and the film thickness of a dielectric film in Examples and Comparative Examples, and FIG. 4 is Examples and Comparative Examples. 3 is a graph showing the relationship between the holding time and the coercive force in FIG. Symbols in the figure: 1,7 …… Transparent substrate 2,4,8,10 …… Dielectric film (layer) 3,9 …… Magnetic film 5 …… Reflective film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tadao Nomura 100-1 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa Shin-Etsu Chemical Co., Ltd. Corporate Research Center (72) Inventor Yoshimasa Shimizu 100 Sakado, Takatsu-ku, Kawasaki-shi, Kanagawa 1 Shin-Etsu Chemical Co., Ltd. Corporate Research Center (72) Inventor Yoshihiro Kubota 2-13-1 Isobe, Annaka-shi, Gunma Shin-Etsu Chemical Co., Ltd. Precision Materials Research Laboratory (72) Inventor Shu Kashida Gunma 2-13-1 Isobe, Annaka-shi, Japan Shin-Etsu Kagaku Kogyo Co., Ltd., Institute for Precision Functional Materials (56) References JP-A-63-18546 (JP, A) JP-A-62-67750 (JP, A) Kai 61-39955 (JP, A) JP 60-191449 (JP, A) JP 3-105744 (JP, A)

Claims (7)

[Claims] 1. A magneto-optical recording medium comprising a dielectric layer, a magnetic film, and a reflective film provided on a transparent substrate placed on the light incident side, wherein the dielectric layer is an amorphous material made of BN containing H. A magneto-optical recording medium characterized by being made of. 2. The amorphous material has a weight composition ratio of B: N: H of 100: 10.
The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium comprises: -30: 5-15. 3. The magneto-optical recording medium according to claim 1, wherein the amorphous material has a refractive index (n) = 1.75 to 2.15. 4. The magneto-optical recording medium according to claim 1, wherein the dielectric layer is formed by a plasma CVD method or a sputtering method. 5. The magneto-optical recording medium according to claim 1, wherein the dielectric layer is formed by a plasma CVD method using ammonia and diborane as raw materials. 6. The magneto-optical device according to claim 1, wherein the dielectric layer is formed by sputtering using BN as a target in an Ar-H ₂ mixed gas atmosphere or an Ar-N ₂ -H ₂ mixed gas atmosphere. recoding media. 7. The dielectric layer targets B, and Ar—N ₂ —H ₂
The magneto-optical recording medium according to claim 1, which is formed by a sputtering method in a mixed gas atmosphere.