JPH08190741A - Method for manufacturing magneto-optical recording medium - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for manufacturing a low noise garnet magneto-optical recording medium on a glass substrate. [Structure] A garnet magneto-optical recording medium composed of an underlayer and a recording layer is formed on a glass substrate, and a heating rate is set to 3 ° C./sec or more and 50 ° C./sec or less when heat-treating and crystallizing the recording layer. . [Effect] A fine-grained garnet film with low medium noise can be uniformly formed on a glass substrate in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high density magneto-optical recording medium using a polycrystalline garnet film and a method for manufacturing a disk.

[0002]

2. Description of the Related Art In a current magneto-optical storage device, an amorphous rare earth transition metal alloy is used as a medium, a semiconductor laser having a wavelength of about 800 nm is used as a light source, and a capacity of about 300 MB on one side of 5.25 inches. Has been realized. However, in order to record and reproduce a large-capacity file such as an image, it is necessary to further increase the density. There are various methods for increasing the density, but the most effective method is to record / reproduce smaller bits with a short wavelength laser beam near 500 nm.

Current amorphous rare earth transition metal alloy materials are
Since the magneto-optical effect used for reproduction decreases at a short wavelength, the reproduction signal becomes small, which is extremely disadvantageous for use in high density magneto-optical recording using a short wavelength laser. on the other hand,
The Bi-substituted rare earth iron garnet film in which the rare earth element is replaced with Bi has a magneto-optical effect that is an order of magnitude larger than that of the existing material at a short wavelength, and has been regarded as one of the promising media for high density magneto-optical recording.

The composition of the Bi-substituted rare earth iron garnet is
It is represented by a general formula of (BiR) ₃ (FeM) ₅ O ₁₂ . Here, R is a rare earth element containing Y, and M is
It is a trivalent metal that can replace Fe. The role of Bi is to increase the magneto-optical effect. Further, the Curie temperature is adjusted by substituting the iron site with Ga or Al so that thermomagnetic writing can be performed. The garnet according to the present invention is represented by the above composition.

The garnet film formed on the glass substrate is
A polycrystalline body composed of large crystal grains of several μm has a problem that medium noise caused by the grain boundaries is large. To overcome this medium noise, laser wavelength (500 nm)
It was necessary to make the crystal grains finer than in the above, so that the grain boundaries could not be recognized by the resolution of the laser beam.

As a method for refining the crystal grains of the garnet film formed on the glass substrate, a high temperature heating method (T. Suzuk
i: J. Appl. Phys., 69 (8), 4756 (1991)), a method of adding Rb (A. Itoh and K. Nakagawa: Jpn. J. Appl. Phy.
s., 31L790 (1992)) and a method of forming a two-layered structure (Japanese Patent Laid-Open No. 5 (1994)
No. 101935).

In order to further reduce the noise of the garnet film which has been made into two layers and has been miniaturized, the film thickness of the underlying layer is 100 nm.
The following is effective (Japanese Patent Application No. 5-60884).
issue). Further, noise can be reduced by setting the Curie temperature to room temperature or lower and photomagnetizing at room temperature (Japanese Patent Application No. 5-96).
718). Furthermore, if Cu is added to the recording layer having a two-layer structure to increase the coercive force, it is possible to write a minute bit of 1 μm or less (JP-A-3-178105).

As described above, various methods have been proposed for reducing the noise by miniaturizing the crystal grains and improving it. However, a method for uniformly forming a low noise garnet film made of the fine crystal grains in a short time is proposed. It has been an issue that has not been examined until now.

Recently, a method has been disclosed in which an amorphous film is formed on a glass substrate or on a glass substrate, and a garnet film is uniformly heat-treated on the glass substrate and crystallized within 60 seconds (Japanese Patent Application Laid-Open No. Hei 5 (1993) -58). Japanese Patent No. 347039, JP-A-6
-20317). However, the garnet film thus formed is composed of large crystal grains and cannot be applied to a magneto-optical recording medium by itself. Therefore, it has been proposed to form a recording layer composed of fine crystal grains on the substrate while keeping it at a high temperature and crystallizing it during film formation.

However, it is extremely burdensome for an industrial production apparatus to carry out film formation while keeping the substrate temperature high. Therefore, it is desirable to produce the medium in a short time by heat treatment crystallization, which is the same manufacturing method as for the base. However, a method for uniformly producing a garnet recording layer made of fine crystal grains on a polycrystalline garnet underlayer by heat treatment crystallization in a short time has not yet been studied.

[0011]

SUMMARY OF THE INVENTION In order to improve the industrial productivity of a garnet magneto-optical recording medium, the present invention provides a recording layer garnet film consisting of fine crystal grains on a garnet underlayer by heat treatment crystallization in a short time, In addition, it is an object of the present invention to provide a manufacturing method for uniformly forming.

[0012]

The present invention is characterized by the following items. A method for manufacturing a magneto-optical recording medium, comprising a garnet underlayer on a glass substrate and a garnet recording layer formed thereon having a grain size of 100 nm or less, wherein a garnet recording layer is laminated in an amorphous state on the garnet underlayer. And 3 ℃
A method for producing a magneto-optical recording medium, which is formed by heat treatment and crystallization at a temperature rising rate of not less than / sec and not more than 50 ° C / sec. The method for producing a magneto-optical recording medium as described above, wherein a garnet recording layer is formed on a garnet underlayer having a lattice constant different by ± 0.3% or more. The above-mentioned method of forming a garnet recording layer on a garnet underlayer having a lattice constant of ± 0.3% or more and a film thickness of 100 nm or less. The garnet recording layer has a lattice constant of ± 0.3.
%, The film thickness is 100 nm or less, and the Curie temperature is room temperature or less, the garnet recording layer is formed on the garnet underlayer. A method for manufacturing a magneto-optical recording medium, which comprises forming a garnet recording layer containing Cu at 5 at% or less with the remaining composition excluding oxygen by any one of the above methods.

The present invention will be described in detail below. The present inventors set the temperature rising rate to a specific range,
We have experimentally found a method for producing a garnet recording layer on a crystallized garnet substrate by heat treatment crystallization within an extremely short time. That is, as a result of trying various heating rates, for example, when the recording layer is crystallized at a heating rate of 20 ° C./second, the time required to completely crystallize the recording layer is about 20 seconds, which is extremely short. It was time (Figure 1). When the temperature rising rate was 3 ° C./sec or more, the crystallization of the recording layer on the underlayer suddenly started, and at the temperature rising rate of 5 ° C./sec or more, the recording layer was completely crystallized by the heat treatment within 30 minutes ( (Figure 3). Normally, it takes a few hours, but the manufacturing time by heat treatment crystallization of the recording layer becomes extremely short by selecting a temperature rising rate of 3 ° C./sec or more on the crystallization base.

Further, the present inventors have experimentally found that when heat-treating and crystallizing a garnet recording layer on a garnet base, the uniformity of the crystal grains of this recording layer also sensitively depends on the temperature rising rate. It was That is, when the recording layer is crystallized at various heating rates, in order to uniformly form a recording layer made of fine particles having a particle diameter of 100 nm on the crystallization base by heat treatment, the heat treatment of the recording layer is crystallized. The rate of temperature rise is 1
It was necessary to set it to ℃ / sec or more.

Therefore, in order to produce a garnet recording layer consisting of crystal grains of 100 nm or less uniformly on a crystallized garnet underlayer formed on a large area substrate by heat treatment crystallization in a short time, at least a temperature rising rate of 3 ° C. It is necessary to set it to / seconds or more.

In the present invention, if the heating rate is 3 ° C./sec or more, the garnet recording layer can be formed uniformly and in a short time on the crystallized garnet base. In fact, 100 ° C /
This was confirmed by the heating rate up to seconds. However,
Considering industrial productivity, the upper limit of the heating rate is 50 ° C.
/ Sec. That is, according to the present invention, by setting the heating rate to 3 ° C./sec or more and 50 ° C./sec or less, a fine-grained recording layer having a grain size of 100 nm or less is uniformly formed on the crystallization base by heat treatment crystallization. It can be manufactured in a short time.

Various crystallized garnet bases can be used to form the garnet recording layer composed of fine grains.
When Rb is added as described above, or when an underlayer made fine by high-speed heating is used, the lattice constant of the recording layer is not limited. When an underlayer having a grain size of several μm prepared by a normal method is used, a difference of ± 0.3% or more is required between the underlayer and the recording layer in order to miniaturize the recording layer. is there. In any case, by setting the heating rate to 3 ° C./sec or more and 50 ° C./sec or less, a recording layer having a grain size of 100 nm or less can be uniformly produced in a short time on the crystallization base by heat treatment crystallization. it can.

In a magneto-optical recording medium using a garnet underlayer composed of large crystal grains, noise due to the underlying crystal grains becomes a problem. In order to eliminate this noise, it is necessary to make the underlayer film thickness 100 μm or less to render the underlayer crystal grain boundaries harmless. When the underlayer exhibits magnetism, the magnetic properties of the two-layer film are a superposition of the underlayer and the garnet recording layer. In the magneto-optical recording medium composed of such a two-layer film, the shape of the written bit may be disturbed and the write noise may increase. In such a case, it is effective to adjust the composition of the underlayer so that the Curie temperature is room temperature or lower to render it non-magnetic.

It is advantageous that the coercive force of the recording layer is large in order to write a minute bit of 1 μm or less. The coercive force can be increased by adding Cu to the recording layer in a composition other than oxygen in an amount of 5 at% or less. In either case, by setting the rate of temperature rise to 3 ° C./sec or more and 50 ° C./sec or less, a recording layer having a grain size of 100 nm or less is uniformly formed in a short time on the crystallization base by heat treatment crystallization. A magneto-optical recording medium with low medium noise can be manufactured with high productivity.

The range of heat treatment temperature in the present invention is 40.
It is 0-750 degreeC. The crystallization temperature of the Bi-substituted garnet film depends on the composition, but the lower limit was 400 ° C. Further, in order to use a heat-resistant glass substrate such as non-alkali glass, it is necessary to set the temperature to 750 ° C. or lower at which the glass substrate does not soften and deform. It is known that when a garnet film is formed by sputtering or the like, the composition becomes a non-stoichiometric composition deviating from the stoichiometric composition of garnet described above. The present invention is also applicable to such a non-stoichiometric garnet film.

[0021]

The present invention will be described in more detail based on the following examples. The film formation was performed by high frequency magnetron sputtering. Sputtering conditions are argon gas pressure: 2 to 10 mT
orr, high frequency power: 3 to 6 W / cm ² . The substrate was rotated during film formation to ensure the uniformity of film thickness. The garnet film was formed in an amorphous state and was heat-treated and crystallized in an atmosphere of argon or a mixture of nitrogen and oxygen.
The oxygen concentration at that time was 20 to 100%, and an infrared lamp heating furnace was used for the heat treatment. Place the glass substrate or the disc on which the film is formed on the support table to measure 400 to 750.
It heat-processed in the temperature range of (degreeC).

An amorphous underlayer was first formed on a glass substrate and heat-treated for crystallization. A recording layer in an amorphous state was laminated on the crystallized underlayer, and heat-treated to crystallize to form a two-layer film. When evaluating the recording / reproducing, C is further added on the recording layer.
A reflective film such as r or Al was laminated. An amorphous film having a garnet composition is nonmagnetic and has a Faraday rotation angle of zero. Since the Faraday rotation angle increases in proportion to crystallization, the crystallization rate can be estimated from the rotation angle. The crystal grain size is an electron microscope,
The presence or absence of a different phase was examined by X-ray diffraction.

Example 1 A two-layer film of combination pattern A shown in Table 1 was examined. The difference between the lattice constants of the underlayer and the recording layer is 1.2%,
The Curie temperature of the underlayer is set to room temperature or lower. A two-layer film in which a recording layer is formed in an amorphous state on a crystallization base,
A single layer film in which only the same recording layer was formed in an amorphous state on a glass substrate was heat-treated and crystallized under the same conditions. The heat treatment conditions are a heating rate of 20 ° C./sec and a heat treatment temperature of 550 ° C. Under this condition, the heat treatment time is 5 seconds to 4 hours (7200
Second) and the Faraday rotation angle was measured. In the case of a two-layer film, the underlayer is nonmagnetic, so the rotation angle is due to the contribution of only the recording layer. The result is shown in FIG.

[0024]

[Table 1]

As shown in FIG. 1, the recording layer in the case of the two-layer film is saturated at the Faraday rotation angle of 1.0 ° in about 20 seconds. At this time, the recording layer consisted only of the garnet phase, and the crystallized recording layer on the garnet base was completely crystallized in about 20 seconds (crystallization rate 100%). On the other hand, the recording layer of the same composition formed directly on the glass substrate had a small rotation angle of 0.25 ° even after 4 hours. Here, when the crystallization rate is estimated from the ratio with the saturation value of the Faraday rotation angle, it is 25
%.

FIG. 2 shows a photograph of a metal structure observed with an optical microscope at 2800 times. Crystal grains of several μm were clearly observed in the recording layer on the glass substrate (FIG. 2A). On the other hand, in the two-layer film, the recording layer is miniaturized to 50 μm, which is less than the resolution of the microscope, and crystal grains cannot be observed (FIG. 2 (b)). At a heating rate of 250 ° C./sec, which is a typical high-speed heating method, the recording layer of the two-layer film was 100% crystallized with fine crystal grains as in FIG. In the case of the single-layer film in which only the recording layer was formed on the substrate, the crystallization rate was low as in the case of FIG. 2A, and the film was not miniaturized.

Example 2 A two-layer film of combination pattern A shown in Table 1 was examined. A recording layer was formed in an amorphous state on a crystallization base 2
The Faraday rotation angle of the single layer film in which only the same recording layer is formed on the glass substrate in an amorphous state on the glass substrate has a Faraday rotation angle of 0.5 ° C./sec.
The comparison was made at a heating rate of 20 ° C./sec. The heat treatment conditions are a heat treatment temperature of 550 ° C. and a heat treatment time of 30 minutes. The result is shown in FIG.

In the recording layer of the two-layer film, crystallization rapidly progresses at a temperature rising rate of 3 ° C./sec or more, and a crystallization rate of 1 at 5 ° C./sec or more.
00%. On the other hand, the recording layer of the single-layer film was hardly crystallized.

Example 3 A magneto-optical disk (5 inches) composed of a two-layer film of combination pattern A shown in Table 1 was prepared. An amorphous recording layer was formed on the crystallization base, and 100% crystallization was performed within 1 minute.
The heat treatment conditions are a heating rate of 30 ° C./sec and a heat treatment temperature of 5
50 ° C. In order to evaluate the recording / reproducing characteristics, a 100 nm Cr reflective layer was laminated on this recording layer. The recording / reproducing characteristics of this disk were examined by an evaluation device equipped with a short wavelength laser (wavelength 488 nm). As a result, 0.5μ
The C / N at a bit length of m is 45 dB or more, which is a sufficient characteristic for high-density digital recording / reproduction.

Example 4 A two-layer film of combination pattern B shown in Table 1 was examined. The lattice constant difference between the underlayer and the recording layer is 0.6%. 100% by forming an amorphous recording layer on the crystallization base
It was crystallized and the homogeneity of the fine grains was investigated. Temperature rising rate is 0.1
˜50 ° C./sec, heat treatment temperature is 560 ° C. When the rate of temperature rise is 0.2 ° C./sec (FIG. 4 (a)), crystal grains of several μm are also observed, which is non-uniform, but when it is 30 ° C./sec (FIG. 4).
In (b), since the recording layer is made of uniform fine particles of 100 nm or less, no structure is observed by an optical microscope.

Example 5 In addition to the composition of the garnet film described above, garnet in which other rare earth elements such as Y, Gd and Tb are substituted for Dy, and garnet in which A and In are substituted for Ga Examined. In any case, when the temperature rising rate was set to 3 ° C./sec or more and 50 ° C./sec or less, the garnet recording layer composed of fine crystal grains could be uniformly formed on the crystallization base in a short time.

[0032]

According to the method of the present invention, a low noise garnet recording layer composed of fine crystal grains can be manufactured on a glass substrate. That is, an amorphous recording layer is formed on a crystallized underlayer, and heat treatment is performed at a temperature rising rate of 3 ° C./sec or more and 50 ° C./sec or less to crystallize the grains from 100 nm or less in a short time. The garnet recording layer can be formed.

[Brief description of drawings]

FIG. 1 is a diagram showing a heat treatment time dependency of a Faraday rotation angle.

FIG. 2 shows the recording layer garnet 2800 of the present invention after heat treatment.
It is a metal crystal structure photograph observed with a 2 times optical microscope.

FIG. 3 is a diagram showing a temperature rise rate dependency of a Faraday rotation angle.

FIG. 4 is a photograph of a metal crystal structure of a recording layer garnet of the present invention which was heat-treated while changing the temperature rising rate, which was observed with an optical microscope at 2800 times.

[Procedure amendment]

[Submission date] March 10, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 4

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

As a method for refining the crystal grains of the garnet film formed on the glass substrate, a high-speed temperature rising method (T. Su.
zuki: J. Appl. Phys. , 69 (8), 4
756 (1991)), a method of adding Rb (A. It.
oh and K. Nakagawa: Jpn. J. A
ppl. Phys. , 31, L790 (1992)) and a method of forming two layers (Japanese Patent Laid-Open No. 5-101935).
There is.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

The present invention is characterized by the following items. A method for manufacturing a magneto-optical recording medium, comprising a garnet underlayer on a glass substrate and a garnet recording layer formed thereon having a grain size of 100 nm or less, wherein a garnet recording layer is laminated in an amorphous state on the garnet underlayer. And 3 ℃
A method for producing a magneto-optical recording medium, which is formed by heat treatment and crystallization at a temperature rising rate of not less than / sec and not more than 50 ° C / sec. The method for producing a magneto-optical recording medium as described above, wherein a garnet recording layer is formed on a garnet underlayer having a lattice constant different by ± 0.3% or more. The above-mentioned method of forming a garnet recording layer on a garnet underlayer having a lattice constant of ± 0.3% or more and a film thickness of 100 nm or less. The garnet recording layer has a lattice constant of ± 0.3.
%, The film thickness is 100 nm or less, and the Curie temperature is room temperature or less. A method for manufacturing a magneto-optical recording medium, which comprises forming a garnet recording layer containing Cu at 5 at% or less with the remaining composition excluding oxygen by any one of the above methods.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

In a magneto-optical recording medium using a garnet underlayer composed of large crystal grains, noise due to the underlying crystal grains becomes a problem. In order to eliminate this noise, it is necessary to make the underlayer film thickness 100 nm or less to render the underlayer crystal grain boundaries harmless. When the underlayer exhibits magnetism, the magnetic properties of the two-layer film are a superposition of the underlayer and the garnet recording layer. In the magneto-optical recording medium composed of such a two-layer film, the shape of the written bit may be disturbed and the write noise may increase. In such a case, it is effective to adjust the composition of the underlayer so that the Curie temperature is room temperature or lower to render it non-magnetic.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction content]

FIG. 2 shows a photograph of a metal structure observed with an optical microscope at 2800 times. Crystal grains of several μm were clearly observed in the recording layer on the glass substrate (FIG. 2A). On the other hand, in the two-layer film, the recording layer is miniaturized to 50 nm, which is less than the resolution of the microscope, and crystal grains cannot be observed (FIG. 2 (b)). At a heating rate of 50 ° C./sec, which is a typical high-speed heating method, the recording layer of the two-layer film was 100% crystallized with fine crystal grains as in FIG. In the case of the single-layer film in which only the recording layer was formed on the substrate, the crystallization rate was low as in the case of FIG. 2A, and the film was not miniaturized.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

Example 5 In addition to the composition of the garnet film described above, a garnet in which other rare earth elements such as Y, Gd and Tb are substituted for Dy, and a garnet in which Al or ln is substituted for Ga are also used. Examined. In any case, when the temperature rising rate was set to 3 ° C./sec or more and 50 ° C./sec or less, the garnet recording layer composed of fine crystal grains could be uniformly formed on the crystallization base in a short time.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a diagram showing a heat treatment time dependency of a Faraday rotation angle.

FIG. 2 shows the recording layer garnet 2800 of the present invention after heat treatment.
It is a crystal structure photograph observed with a double optical microscope.

FIG. 3 is a diagram showing a temperature rise rate dependency of a Faraday rotation angle.

FIG. 4 is a crystal structure photograph of a garnet of the recording layer of the present invention, which was heat-treated while changing the temperature rising rate, observed with an optical microscope at 2800 times.

Claims (5)

[Claims] 1. A method for manufacturing a magneto-optical recording medium comprising a garnet underlayer on a glass substrate and a garnet recording layer formed thereon having a grain size of 100 nm or less as a constituent unit. A method for manufacturing a magneto-optical recording medium, which is characterized in that the magneto-optical recording medium is laminated on a garnet base and heat-treated and crystallized at a heating rate of 3 ° C./sec or more and 50 ° C./sec or less. 2. The method of manufacturing a magneto-optical recording medium according to claim 1, wherein a garnet recording layer is formed on a garnet underlayer having a lattice constant different by ± 0.3% or more. 3. The method of manufacturing a magneto-optical recording medium according to claim 1, wherein a garnet recording layer is formed on a garnet underlayer having a lattice constant different by ± 0.3% or more and a film thickness of 100 nm or less. 4. The garnet recording layer according to claim 1, which has a lattice constant different by ± 0.3% or more, a film thickness of 100 nm or less, and a Curie temperature of room temperature or less. The method of manufacturing a magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is formed. 5. A method of manufacturing a magneto-optical recording medium, which comprises forming a garnet recording layer containing Cu at 5 at% or less with the remaining composition excluding oxygen by any one of claims 1 to 4.