JP2861807B2 - Method for manufacturing magneto-optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magneto-optical recording medium, and more particularly to a method for reading a magneto-optical effect such as a magnetic Kerr effect or a magnetic Faraday effect, which is used for a rewritable magneto-optical disk or the like. The present invention relates to a method for manufacturing a magnetic recording medium.

[0002]

2. Description of the Related Art The material of a magneto-optical recording medium mainly requires the following conditions. (A) A perpendicular magnetization film. (B) have a large coercive force; (C) The car rotation angle is large.

It is known that when heavy rare earth elements such as Tb, Gd, etc. are added to Fe, Co, etc., the magnetic anisotropy increases to form a perpendicular magnetization film. From these facts, GdTbFe, DyFe, GdCo, Gd
A heavy rare earth-3d transition metal amorphous alloy thin film of Co, TbCo, TbFeCo, or the like satisfies the above conditions, is suitable for mass production, and is considered to be promising because of its low readout noise. In particular, TbFeCo is promising and has become a practical material.

As a means for increasing the density of magneto-optical recording, there is a method of miniaturizing a recording area by narrowing a laser beam diameter. N.P. of the objective lens of the recording / reproducing head A. In order to narrow the beam diameter without changing the wavelength, it is necessary to shorten the wavelength of the laser light source. For this reason, short-wavelength light sources and short-wavelength LDs using nonlinear optical elements have been developed. However, it is known that a heavy rare earth-3d transition metal amorphous alloy thin film currently in practical use has a smaller Kerr rotation angle as the wavelength becomes shorter. Further, the quantum conversion efficiency of the photodetector also decreases due to the decrease in wavelength. Therefore, when reproduction is performed using a short-wavelength laser, the reproduction output is greatly reduced, and it is difficult to achieve a high recording density. Therefore, a new magneto-optical recording material having a large Kerr rotation angle in a short wavelength region is required.

[0005] Garnet, Pt / Co, and light rare earth-3d transition metal amorphous alloy thin films have been studied as magneto-optical recording materials for short wavelengths. However, these materials have the following disadvantages.

[0006] Garnet has a large Faraday rotation angle so that a large reproduction output can be obtained. However, in order to grow a crystal during or after film formation, heating at 600 ° C or higher is required, and a garnet must be heated on a normal glass substrate. It is difficult to make. Therefore, it is necessary to use expensive heat-resistant glass as the substrate, and there is a disadvantage that the medium becomes expensive.

Pt / Co is heavy rare earth-3d in a short wavelength region.
It has a Kerr rotation angle larger than that of the transition metal amorphous alloy, but is not large enough to compensate for a decrease in the conversion efficiency of the photodetector. In addition, since it is crystalline, medium noise is large, and there is a disadvantage that the reproduction output in a short wavelength range is reduced (Japanese Patent Laid-Open No. Hei 3-162739).

In the case of the light rare earth-3d transition metal amorphous alloy thin film, similarly to the case of Pt / Co, there is a drawback that a sufficiently large Kerr rotation angle cannot be obtained in a composition range where recording and reproduction are possible. Therefore, it is necessary to use a new material instead of these recording materials.

The MnBi compound is formed by heating and reacting a Mn—Bi laminated film in which Bi and Mn are sequentially formed on a substrate.
The C-axis orientation of Bi is preserved, resulting in a C-axis oriented MnBi compound. Since this MnBi compound has strong magnetic anisotropy in the C axis, it becomes a perpendicular magnetization film. Further, MnB
The i-compound is promising as a short-wavelength magneto-optical recording material because the Kerr rotation angle is as large as 1 degree or more between 400 nm and 900 nm.

[0010]

A method of manufacturing a MnBi magneto-optical recording medium and a noise level will be described with reference to the drawings. FIG. 15 is a sectional view showing the configuration of a conventional MnBi magneto-optical recording medium before heat treatment. On a glass substrate 1, an underlayer (silicon nitride film by sputtering) 2 has a thickness of 100 nm, a Bi layer 3 has a thickness of 20 nm by an ion cluster beam method, and a Mn layer 4 has a thickness of 8 nm by an ion cluster beam method. The thickness of the interference layer (SiN by sputtering) 5 is set to 300 nm.
The reflective layer (Al film by sputtering) 6 to a thickness of 20
Films were sequentially formed to a thickness of nm. Mn deposition rate is 0.05nm
/ S, and the degree of vacuum during film formation is 3.times.10@-6 torr. B
The film formation speed of i is 0.1 nm / s, and the degree of vacuum during film formation is 3 × 1
0-7 torr. The substrate temperature during the formation of Bi is room temperature. The slope angle between the land and groove boundary slope is 1
A 1.7 degree substrate was used.

FIG. 16 shows a noise spectrum (a) of a disk of a MnBi magneto-optical recording medium together with a noise spectrum (b) of a TbFeCo disk which is a general magneto-optical disk medium. Measurement wavelength 830nm,
The NA of the objective lens is 0.55, the linear velocity is 6 m / s, and the measurement is performed under the condition that the reproduction light amount is constant. The noise level of the MnBi disk is larger than that of the TbFeCo disk and 1 MHZ.
It is recognized that there is a difference of 20 dB near z. There is also a disadvantage that the reproduction signal noise ratio (C / N) is small.

An object of the present invention is to provide a simple method for producing a MnBi magneto-optical recording medium which has low medium noise and is practically used.

[0013]

According to the present invention, there is provided a magneto-optical device in which a base layer made of a dielectric material, a Bi layer, an Mn layer, and an interference layer made of a dielectric material are sequentially formed on a substrate, and a MnBi compound is synthesized by heat treatment. This is a method for manufacturing a recording medium, and is particularly made by considering a Bi layer.

That is, in the above-mentioned method for manufacturing a magneto-optical recording medium, the surface roughness of the Bi layer is reduced to a maximum roughness Rmax <30.
It has been found that a magneto-optical recording medium with reduced medium noise can be obtained by setting the average roughness Ra and the center plane average Ra <2.0 nm. Here, the thickness of the Bi layer is set to 12 nm or more and 1
8 nm or less, or the contact angle with molten Bi is 13
A more suitable magneto-optical recording medium can be obtained by using an underlayer at an angle of 0 ° or more.

In a similar method for manufacturing a magneto-optical recording medium, the substrate temperature during the formation of the Bi layer is set to 80 ° C. or more and 200 ° C. or less, or the film formation rate of the Bi layer is set to 0.1 nm /
It has been found that a magneto-optical recording medium with reduced medium noise can be obtained by setting the value to s or less.

In the same method for manufacturing a magneto-optical recording medium, the Bi layer is formed by dividing the Bi layer into two layers, a Bi underlayer and a Bi growth layer. More preferably, the Bi layer is formed during the formation of the Bi underlayer. Desirable magneto-optical recording media can also be obtained by lowering the substrate temperature below the substrate temperature during the formation of the Bi growth layer, or by setting the film formation rate of the Bi underlayer higher than that of the Bi growth layer.

Furthermore, when a similar magneto-optical recording medium is manufactured using a substrate with a guide groove, the inclination angle between the land and groove boundary slope of the substrate with a guide groove is set to 10 degrees or less, or Bi. The layer is divided into two layers, a Bi underlayer and a Bi growth layer, the substrate temperature during the formation of the Bi underlayer is higher than the substrate temperature during the formation of the Bi underlayer, and the film formation rate of the Bi underlayer is reduced. It has been found that a suitable magneto-optical recording medium can be obtained by lowering the film formation rate of the Bi growth layer.

[0018]

The surface morphology of the Bi thin film is very sensitive to film forming conditions (substrate temperature, film forming rate), surface energy and surface roughness of the underlayer. Therefore, under general film forming conditions, a large number of island-like protrusions having a height equal to or greater than the thickness of the recording film exist on the Bi layer.
For reading recorded information from the magneto-optical recording medium, a change in the polarization plane of the read laser light is used. M on this Bi layer
Since the recording medium is formed by heat treatment after laminating the n-layer and the protective layer, if the island-like protrusions exist on the Bi layer, the island-like protrusions are preserved in the recording layer as they are. For this reason, the polarization plane of the laser light is greatly disturbed at the island-shaped projections, and high medium noise is generated. Therefore, MnB is formed by the planarization of the Bi layer.
The medium noise of the i-disk can be reduced.

The flatness of the Bi layer strongly depends on the frequency of crystal nucleation and its growth rate. In other words, the lower the nucleation frequency and the lower the growth rate, the higher the flatness and the fewer the island-like protrusions. In order to reduce the nucleation frequency, it is effective to reduce the surface energy of the underlayer, in other words, to reduce the wettability (corresponding to a large contact angle with Bi). In addition, since the island-like projections are generated from crystal grain boundaries having a certain thickness or more, it is effective to reduce the thickness of the Bi layer. However, when the thickness is 12 nm or less, crystal growth of MnBi becomes difficult. Increasing the substrate temperature also reduces the frequency of nucleation and is effective in flattening the Bi layer. Slowing the film formation rate means reducing the growth rate of crystal nuclei,
The surface smoothness of the Bi layer is improved.

Separately, it is very effective to separately form the Bi layer into the underlayer and the growth layer because the crystal nucleus density and the growth rate can be controlled separately. The substrate temperature during the formation of the underlayer is lower than the substrate temperature of the growth layer,
The surface smoothness of the Bi layer is improved by setting the film formation rate of the underlayer higher than that of the growth layer.

To reduce the frequency of nucleation, it is also effective to increase the surface flatness of the underlayer. Since the guide groove existing in the substrate changes the inclination of the substrate surface greatly, the frequency of generation of crystal nuclei is increased. Therefore, the occurrence of island-like protrusions can be suppressed by reducing the inclination angle of the slope between the land and the groove. It is also effective to suppress the growth of island-like projections by growing a thick growth layer at a high deposition rate after forming a Bi layer having high flatness as a thin underlayer.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a MnBi magneto-optical recording medium and the recording medium will be described with reference to the drawings. FIG. 1 shows M
FIG. 3 is a cross-sectional view illustrating a configuration of an nBi magneto-optical recording medium before heat treatment.
Glass substrate 1 with grooves formed by photopolymer
An underlayer (silicon nitride film formed by sputtering) 2 is
The Bi layer 3 has a thickness of 15 nm by the ion cluster beam method, the Mn layer 4 has a thickness of 6 nm by the ion cluster beam method, and the interference layer (SiO by the ion cluster beam method) 5 has a thickness of 300 nm. A reflective layer (Al film by sputtering) 6 was sequentially formed to a thickness of 20 nm. M
The deposition rate of n is 0.2 nm / s, and the degree of vacuum during deposition is 1 × 1.
0 ^-6 torr. The Bi deposition rate is 0.045 nm /
s, the degree of vacuum during film formation is 3 × 10 ⁻⁷ torr, and the substrate temperature is 130 ° C. Heat treatment was performed at 150 ° C. for 10 hours to obtain a recording medium. The surface roughness of the Bi layer can be changed by changing the thickness of the Bi layer, the film formation conditions, and the underlayer.

FIG. 2 shows an AFM image (1 μm × 1 μm) of the Bi layer.
m) is an example. The Bi deposition rate is 0.045 nm /
s, the degree of vacuum during film formation is 3 × 10 ⁻⁷ torr, the substrate temperature is room temperature, and the layer thickness is 15 nm. A glass substrate is used.
It can be seen that island-like protrusions having a size of about 50 nm are scattered. These island-shaped protrusions cause the medium noise to increase. The Bi layer has Rmax = 15 nm and Ra = 1.73.

FIG. 3 shows the relationship between Rmax and Ra in the MnBi magneto-optical disk in which the surface roughness of the Bi layer is changed by changing the thickness of the Bi layer, the film forming conditions and the underlayer.
The medium configuration is the same as that of FIG. 1 except for the thickness of the Bi layer. Measurement wavelength 830nm, objective lens NA 0.55, linear velocity 6m
/ S and a constant reproduction light amount. This is the value of the noise level at 1 MHz. The medium noise is Rmax <3
0-35 dB or less in the range of 0 nm and Ra <2.0 nm,
Noise is lower than in the conventional example shown in FIG. This means that the surface roughness of the Bi layer is reduced to Rmax <30 nm and Ra <2.0.
This indicates that the medium noise can be reduced by setting nm.

FIG. 4 shows that the deposition rate of Bi is 0.1 nm / s,
The layer thickness and Rmax of the Bi surface when the substrate temperature is room temperature,
The relationship of Ra is shown. A glass substrate is used. 1 layer thickness
Below 8 nm, Rmax <30 nm and Ra <2.0 nm.
The medium noise of the MnBi disk can be reduced. On the other hand, when the Bi layer has a thickness of 12 nm or less, Bi
And Mn did not proceed uniformly, and a MnBi disk could not be produced. Therefore, in order to reduce the medium noise and manufacture the MnBi disk, the thickness of the Bi layer is set to 1
It is necessary to be 2 nm or more and 18 nm or less.

FIG. 5 shows the relationship between the contact angle θ between the molten Bi, the underlayer and the substrate, and Ra and Rmax. Deposition rate of 0.05
nm / s and the substrate temperature was 130 ° C. The thickness is 20 nm. The horizontal axis indicates 1 + cos θ which is proportional to the surface energy. Ra and Rmax increase with increasing 1 + cos θ. If 1 + cos θ is 0.4 or less, Rmax <
30 nm, Ra <2.0 nm, and the medium noise of the MnBi disk can be reduced. This is the contact angle θ
Corresponds to 130 degrees or more.

FIG. 6 shows the relationship between the substrate temperature and Rmax during Bi film formation. The deposition rate is 0.05 nm / s, and the film thickness is 20 nm.
It is. Rmax decreases with increasing substrate temperature.
When the substrate temperature is 80 ° C. or less, Rmax <30 nm and M
The medium noise of the nBi disk can be reduced. On the other hand, when the substrate temperature was 200 ° C. or higher, the melting point of Bi was close to that, so the C-axis orientation of the Bi layer was lost, and it could not be used for producing a MnBi disk.

FIG. 7 shows the relationship between the Bi deposition rate and Rmax. The substrate temperature is 130 ° C., and the film thickness is 20 nm. Rmax
Increases with an increase in the deposition rate. When the deposition rate is 0.
At 1 nm / s or less, Rmax <30 nm, and the medium noise of the MnBi disk can be reduced.

FIG. 8 shows an AFM image (1 .mu.m.times.1 .mu.m) of a Bi layer formed into two layers, an underlayer and a growth layer. FIG. 9 shows an AFM image (1 μm × Bi) of a Bi layer formed by normal continuous film formation.
1 μm). The conditions for forming the underlayer are as follows.
19 nm / s, substrate temperature: room temperature, layer thickness: 5 nm. The growth conditions for the growth layer are as follows: film formation rate: 0.045 nm / s, substrate temperature: 130 ° C., and layer thickness: 15 nm. The film formation conditions for the normal continuous film formation of the Bi layer are a film formation rate: 0.045 nm / s, a substrate temperature: 130 ° C., and a layer thickness: 20 nm. A glass substrate was used. As can be seen from the AFM image, the film is divided into two layers, ie, the underlayer and the growth layer.
The surface smoothness of the i-layer increases, and the medium noise of the MnBi disk can be reduced.

FIG. 10 shows an AFM image (1 μm × 1 μm) of the Bi layer in which the conditions for forming the underlayer and the growth layer are reversed.
The conditions for forming the underlayer in this case are as follows:
nm / s, substrate temperature: 130 ° C., layer thickness: 5 nm. The deposition conditions for the growth layer are as follows: deposition rate: 0.19 nm / s, substrate temperature: room temperature, and layer thickness: 15 nm. A glass substrate was used.
As can be seen from the AFM image, under these film forming conditions, the surface smoothness of the Bi layer is worse than in the normal continuous film formation, and the medium noise of the MnBi disk cannot be reduced. Therefore, the substrate temperature during the formation of the underlayer is set lower than the substrate temperature of the growth layer, and the formation rate of the underlayer is set higher than the formation rate of the growth layer. B formed
It is necessary to improve the surface smoothness of the i-layer.

FIG. 11 shows the A layer of a Bi layer grown on a substrate having a slope of 9.5 degrees between the land and the groove.
It is an FM image (10 μm × 10 μm). The film formation speed of Bi is 0.045 nm / s, and the degree of vacuum during film formation is 3 × 10 ⁻⁷ to.
rr, the substrate temperature is 100 ° C., and the layer thickness is 20 nm. A polycarbonate substrate is used. The surface flatness of the Bi layer is high, and there is no island-like projection at the boundary between the land and the groove.

FIG. 12 is an example of an AFM image (10 μm × 10 μm) of a Bi layer grown on a substrate having an inclination angle of 11.7 degrees between the land and the groove. The film formation speed of Bi is 0.045 nm / s, and the degree of vacuum during film formation is 3 × 1.
0 ^-7 torr, the substrate temperature is 100 ° C., and the layer thickness is 20 nm. A glass substrate having a guide groove made of photopolymer is used. It can be seen that island-like protrusions have grown at the boundary between the land and the groove. The height of the island-shaped protrusion from the flat portion is 64 nm.

FIG. 13 shows the relationship between the inclination angle of the slope between the land and the groove and the height of the Bi island-like projection from the flat portion. As the inclination angle increases, the height of the Bi island-shaped protrusions increases. By setting the inclination angle to 10 degrees or less , the height of the island-shaped protrusions becomes 30 nm or less, and the medium noise of the MnBi disk can be reduced.

FIG. 14 shows an AFM image (10 μm × 10 μm) of a Bi layer grown on an underlayer and a growth layer on a substrate having an inclination angle of 11.7 degrees between the land and the groove.
) Is an example. The conditions for forming the underlayer are as follows:
0.045 nm / s, substrate temperature: 130 ° C., layer thickness: 5 nm. The growth conditions for the growth layer were as follows: deposition rate: 0.19 nm /
s, substrate temperature: room temperature, layer thickness: 15 nm. The degree of vacuum during the film formation is 3 × 10 ⁻⁷ torr. A glass substrate having a guide groove made of photopolymer is used. The surface flatness of the Bi layer is high, and there is no island-like projection at the boundary between the land and the groove.

[0035]

As described above, according to the manufacturing method of the present invention, in the high-performance magneto-optical recording medium using the MnBi recording layer, the reproduction signal noise ratio can be improved by reducing the medium noise. .

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a magneto-optical recording medium according to the present invention before heat treatment.

FIG. 2 is a diagram showing an example of an AFM image (1 μm × 1 μm) of a Bi layer.

FIG. 3 shows medium noise and Rmax of a MnBi magneto-optical disk.
, Ra. FIG.

FIG. 4 is a diagram showing the relationship between the Bi layer thickness and Rmax and Ra of the Bi layer surface.

FIG. 5 is a diagram showing the relationship between Bi, the contact angle θ between the underlayer and the substrate, and Ra and Rmax on the surface of the Bi layer.

FIG. 6 shows the relationship between the substrate temperature during Bi film formation and the Bi layer surface Rmax.

FIG. 7 is a graph showing a relationship between a Bi film forming speed and a Bi layer surface Rmax.

FIG. 8 is an AFM image (1 μm) of a Bi layer formed into two layers.
m × 1 μm).

FIG. 9 is an AFM image (1 μm × Bi image) of a normal continuous film-forming Bi layer.
1 μm).

FIG. 10 is an AFM image (1 μm × 1 μm) of a Bi layer in which the film forming conditions of the underlayer and the growth layer are reversed from those of FIG.

FIG. 11 is an AFM image (10 μm × 10 μm) of a Bi layer on a substrate in which the inclination angle of the land and groove boundary slope is 9.5 degrees.
m).

FIG. 12 is an AFM image (10 μm × 10 μm) of a Bi layer on a substrate having an inclination angle of 11.7 degrees between the land and the groove boundary slope.
μm).

FIG. 13 shows the relationship between the inclination angle of the slope between the land portion and the groove portion and the height of the Bi island-like protrusion from the flat portion.

FIG. 14 is an AFM image (10 μm × 10 μm) of a Bi layer grown on an underlayer and a growth layer on a substrate having an inclination angle of 11.7 degrees between a land portion and a groove portion.

FIG. 15 is a partial cross-sectional view of a conventional magneto-optical recording medium before heat treatment.

FIG. 16 is a diagram showing a noise spectrum of a magneto-optical recording medium.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 glass substrate 1 ′ glass substrate having grooves formed by photopolymer 2 underlayer 3 Bi layer 4 Mn layer 5 interference layer 6 reflective film

Claims (10)

(57) [Claims] An underlayer made of a dielectric material, a Bi layer,
A method for manufacturing a magneto-optical recording medium in which a Mn layer and an interference layer made of a dielectric are sequentially formed and a MnBi compound is synthesized by heat treatment, wherein the surface roughness of the Bi layer is set to a maximum roughness Rmax <3.
A method for manufacturing a magneto-optical recording medium, wherein 0 nm and center plane average roughness Ra <2.0 nm. 2. The method for manufacturing a magneto-optical recording medium according to claim 1, wherein the thickness of the Bi layer is 12 nm or more and 18 nm or less. 3. The method for manufacturing a magneto-optical recording medium according to claim 1, wherein an underlayer having a contact angle with molten Bi of 130 degrees or more is used. 4. An underlayer comprising a dielectric, a Bi layer,
A method for manufacturing a magneto-optical recording medium in which a Mn layer and an interference layer made of a dielectric material are sequentially formed and a MnBi compound is synthesized by heat treatment, wherein the substrate temperature during the formation of the Bi layer is 80 ° C.
A method for producing a magneto-optical recording medium, wherein the temperature is set to 0 ° C. or lower. 5. An underlayer made of a dielectric material, a Bi layer,
A method for manufacturing a magneto-optical recording medium in which an Mn layer and an interference layer made of a dielectric material are sequentially formed and a MnBi compound is synthesized by heat treatment, wherein the film formation rate of the Bi layer is set to 0.1 nm / s or less. A method for manufacturing a magneto-optical recording medium. 6. An underlayer made of a dielectric, a Bi layer,
A method for manufacturing a magneto-optical recording medium in which an Mn layer and an interference layer made of a dielectric material are sequentially formed and a MnBi compound is synthesized by heat treatment, wherein the Bi layer is divided into two layers, a Bi underlayer and a Bi growth layer. A method for manufacturing a magneto-optical recording medium, comprising forming a film. 7. The method according to claim 6, wherein the substrate temperature during the formation of the Bi underlayer is lower than the substrate temperature during the formation of the Bi growth layer. 8. The method for manufacturing a magneto-optical recording medium according to claim 6, wherein the film formation rate of the Bi underlayer is higher than that of the Bi growth layer. 9. A method of manufacturing a magneto-optical recording medium in which a base layer made of a dielectric, a Bi layer, an Mn layer, and an interference layer made of a dielectric are sequentially formed on a substrate having a guide groove, and a MnBi compound is synthesized by heat treatment. A method of manufacturing a magneto-optical recording medium, wherein an inclination angle of a boundary slope between a land portion and a groove portion of the substrate with a guide groove is 10 degrees or less. 10. A magneto-optical recording medium wherein a base layer made of a dielectric, a Bi layer, an Mn layer, and an interference layer made of a dielectric are sequentially formed on a substrate having a guide groove, and a MnBi compound is synthesized by heat treatment. , The Bi layer is divided into two layers, a Bi underlayer and a Bi growth layer, the substrate temperature during the formation of the Bi underlayer is higher than the substrate temperature during the formation of the Bi growth layer, and the Bi underlayer is formed. A method for manufacturing a magneto-optical recording medium, wherein the speed is lower than the film forming speed of a Bi growth layer.