JP3146219B2 - 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 magneto-optical recording medium such as a magneto-optical disk capable of recording, reproducing, and erasing various information such as numerical values, documents, images, music, etc. by irradiating a laser beam or the like.
In particular, the present invention relates to a method for manufacturing a magneto-optical recording medium in which the recording / reproducing characteristics are unlikely to be deteriorated even when erasing, recording, and reproducing are repeated one million times or more.

[0002]

2. Description of the Related Art A magneto-optical recording medium capable of recording, reproducing, and erasing information by using a light beam such as a laser beam enables high-density information recording. It has excellent information processing ability such as being able to do it.

A configuration example of this magneto-optical recording medium will be described below with reference to the drawings. As shown in FIG. 9, a transparent substrate 10 made of glass or plastic, and a magneto-optical effect formed on the transparent substrate 10 are formed. A dielectric interference film 20 for increasing the magnetic field, a magneto-optical recording film 30 formed on the dielectric interference film 20 and having an easy axis of magnetization perpendicular to the film surface, and a magneto-optical recording film 30 formed on the magneto-optical recording film 30. The dielectric protection film 40 for protecting the magneto-optical recording film 30 forms a main part. In FIG. 9, reference numeral 50 denotes a reflection film that reflects laser light.

In order to record information using this magneto-optical recording medium, the magneto-optical recording medium is irradiated with a light beam such as a laser beam to partially heat the magneto-optical recording film 30 so that the magnetization is reduced. When the temperature approaches the disappearing Curie temperature, a bias magnetic field is applied to invert the magnetization of the site.On the other hand, to erase the recorded information, a bias magnetic field in the opposite direction to that during recording is applied to reverse the magnetization of the site. To do this.

[0005]

By the way, in a conventional magneto-optical recording medium, erasing, recording, and reproducing are continuously performed for one time.
When it is repeated about one million times, the thermal sensitivity and the magnetic field sensitivity are liable to change with time.
There is a disadvantage that the reproduction characteristics are deteriorated, and there is a problem that the CNR (carrier noise ratio) of a newly recorded signal is lower than that of an initially recorded signal.

[0006] In particular, in a magneto-optical recording medium, there are an area where recording and erasing are performed frequently and an area where rewriting is not so often performed. There is a problem that a plurality of different recording areas coexist and the CNR of a recorded signal varies depending on the area.

The present invention has been made in view of such a problem, and it is an object of the present invention that the deterioration of the recording / reproducing characteristics is not caused even when erasing, recording, and reproducing are repeated more than 1,000,000 times continuously. An object of the present invention is to provide a method of manufacturing a magneto-optical recording medium which is unlikely to occur.

[0008]

Under the above technical background, the present inventors have conducted intensive analysis on the cause of the temporal change in the thermal sensitivity and the magnetic field sensitivity. Irradiation of a light beam such as light heats the magneto-optical recording film of the magneto-optical recording medium, and the amorphous structure changes due to the temperature rise (annealing), and the magnetic characteristics, especially the coercive force, decrease with this structural change. It is thought that the cause is the decrease in the domain wall coercive force, which is substantially proportional to the coercive force.

Therefore, the present inventors have repeatedly performed erasure, recording, and reproduction for one track one million times continuously using a laser beam whose beam spot diameter corresponds to one track width (hereinafter referred to as erasure, recording, and reproduction). (A test in which E is continuously repeated is referred to as an E / W / R cycle test.) A magneto-optical recording medium whose thermal sensitivity and magnetic field sensitivity have changed is determined, and 600 tracks (about 1 mm width) of this magneto-optical recording medium are further determined. When the E / W / R cycle test was performed 10,000 times, and the Kerr rotation angle of the test portion was measured by a Kerr rotation angle measuring device having a laser spot diameter of 0.1 mm, the coercive force decreased as expected. I was able to confirm that.

[0010] The deterioration of the magnetic characteristics due to the temperature rise (annealing) is hereinafter referred to as annealing deterioration.

The decrease in the coercive force adversely affects the thermal sensitivity of the magneto-optical recording medium and the reproduction stability of the recording magnetic domain, and the decrease in the domain wall coercive force deteriorates the reproduction stability and changes the magnetic field sensitivity. Conceivable.

On the basis of such technical viewpoints, the present inventors conducted detailed studies on a magneto-optical recording film which is unlikely to undergo annealing deterioration, and found that the rare earth-transition metal alloy film constituting the magneto-optical recording film was sputtered. It has been found that when forming a film, a magneto-optical recording film that does not easily undergo annealing deterioration by heating the substrate temperature to 80 ° C. or higher is required. This is because increasing the film forming temperature of the magneto-optical recording film to 80 ° C. or higher increases the density of the formed magneto-optical recording film, and accordingly, the structure of the magneto-optical recording film is stabilized and E / W / R
It is considered that the movement of atoms due to the cycle becomes difficult to occur.

As described above, the film forming temperature of the magneto-optical recording film is set to 80 ° C.
By raising the above, a magneto-optical recording film was obtained in which annealing degradation hardly occurred. On the other hand, as the substrate temperature when forming the magneto-optical recording film was increased, the magneto-optical recording film was maintained during the film formation. When the magnetic force decreases and the substrate temperature is set to 80 ° C. or higher, the coercive force decreases from 1 kOe to several kOe as compared with the case where the film is formed at room temperature. As a result, the recording magnetic domain is easily erased and the recording magnetic domain becomes It has also been found that there is an adverse effect that the reproduction stability decreases with time.

It has been confirmed from a composition analysis of the formed magneto-optical recording film that this decrease in coercive force is not a chemical change such as oxidation. In addition, it has been confirmed from the measurement of the anisotropic magnetic field in the magneto-optical recording film that the anisotropic magnetic field has been reduced. From these analyses, it is considered that the coercive force was reduced due to mechanical causes such as structural or stress of the magneto-optical recording film.

Therefore, when heating the film forming temperature of the above-mentioned magneto-optical recording film to 80 ° C. or more, the present inventors, when forming the magneto-optical recording film and the dielectric interference film adjacent thereto, The inventors have found that a decrease in the coercive force of the magneto-optical recording film can be prevented by positively generating a stress due to a difference in coefficient of thermal expansion between the dielectric protective film and the present invention, and have completed the present invention. is there.

That is, according to the first aspect of the present invention, a dielectric interference film and a rare earth-transition metal alloy formed on the dielectric interference film and having an easy axis of magnetization perpendicular to the film surface are main components. Assuming a method for manufacturing a magneto-optical recording medium and a magneto-optical recording medium having a dielectric protective film formed on the magneto-optical recording film on a substrate, a material having a higher coefficient of thermal expansion than the dielectric interference film After forming the dielectric interference film on the substrate by the sputtering method, the substrate is heated to 80 ° C. or more, and magneto-optical recording is performed on the dielectric interference film under the temperature conditions. A film and a dielectric protection film are sequentially formed by a sputtering method.

In the invention according to the first aspect, the dielectric interference film and the dielectric protection film are made of a material which is transparent and protects the magneto-optical recording film from deterioration such as oxidation. For example, SiNx, AlN , SiO ₂ , SiO, Ta ₂ O ₅ ,
Dielectric materials such as AlO ₃ , SiAlN, and SiAlON are exemplified.

On the other hand, the above-mentioned magneto-optical recording material is, as in the prior art,
An amorphous alloy of a rare earth element such as gadolinium (Gd), terbium (Tb) or dysprosium (Dy) and a transition metal element such as iron (Fe) or cobalt (Co) is applied. For example, GdTbFe, TbDyFe, TbFeC
o, ternary alloys such as DyFeCo, GdTbFeC
quaternary alloys such as o, TbDyFeCo and GdDyFeCo.

In the invention according to claim 1, the substrate is heated to 80 ° C. or higher after forming a dielectric interference film on the substrate, and the substrate is heated at the time of forming the dielectric interference film. Therefore, even if a substrate having a higher coefficient of thermal expansion than the above-mentioned dielectric interference film such as a polycarbonate substrate is applied, the adhesion between the substrate and the dielectric interference film formed thereon becomes weaker, and The resulting stress also has a small value.

After forming the dielectric interference film, the substrate is heated to 80 ° C. or higher, and a magneto-optical recording film and a dielectric protection film are sequentially formed on the dielectric interference film under the temperature condition. Therefore, it is possible to prevent annealing deterioration of the magneto-optical recording film. The coefficient of thermal expansion of the magneto-optical recording material that forms the magneto-optical recording film and contains a rare earth-transition metal alloy as a main component is higher than that of the dielectric material that forms the dielectric interference film and the dielectric protection film. Since a stress (film stress) is generated between the dielectric interference film and the magneto-optical recording film and between the magneto-optical recording film and the dielectric protective film due to a difference in coefficient of thermal expansion, The substrate temperature at which the magneto-optical recording film is formed is 8
The coercive force of the magneto-optical recording film is prevented from decreasing due to the action of the stress despite the temperature being set to 0 ° C. or higher (the coercive force is reduced).
(It becomes possible to increase about 1 kOe or more) . In the present invention, the film forming temperatures of the dielectric interference film and the dielectric protective film are different, and the difference in film density caused by the difference in film forming temperature, that is, the difference in the average interatomic distance, causes the dielectric interference. It is considered that the stress acting between the film and the magneto-optical recording film is not the same as the stress acting between the magneto-optical recording film and the dielectric protective film. There was no problem in increasing the coercive force.

Further, the film formation temperature of the magneto-optical recording film 80
It was confirmed that the reduction of the coercive force in the magneto-optical recording film could not be prevented when the film was formed at a temperature of about ℃ or more and the dielectric protective film was formed by sputtering at a temperature of about room temperature. This is because the dielectric protective film was formed by sputtering on the magneto-optical recording film under a temperature condition of about room temperature.
This is probably because the adhesion between the dielectric protective film and the magneto-optical recording film was weakened and the internal stress of the dielectric protective film was not sufficiently transmitted to the magneto-optical recording film. The magneto-optical recording medium manufactured under such conditions has a film forming temperature of 8 for the magneto-optical recording film.
Since the temperature is set to 0 ° C. or higher, it is possible to prevent annealing deterioration. Even if erasing, recording, and reproducing are repeated more than 1,000,000 times, the recording / reproducing characteristics are hardly deteriorated. Since the decrease cannot be prevented, when the reproduction of the recorded information is repeated about 1 million times continuously, the reproduced signal is deteriorated with time. Therefore, in the present invention, each of these films is successively formed by a sputtering method under a temperature condition at which an internal stress occurs between the dielectric interference film and the magneto-optical recording film and between the magneto-optical recording film and the dielectric protective film. It is necessary to form a film.

In the present invention, the substrate is
A material with a higher coefficient of thermal expansion than the dielectric interference film is applied.
Because, when the sputtering film forming a dielectric interference film on the substrate at this temperature condition heated above 80 ° C. the substrate,
An internal stress opposite to the effect of increasing the coercive force of the magneto-optical recording film may be generated between the substrate and the dielectric interference film, making it impossible to increase the coercive force of the magneto-optical recording film. Therefore, in the present invention, the above dielectric interference film is formed.
After that, it is necessary to heat the substrate to 80 ° C. or higher.

As described above, according to the first aspect of the present invention, it is possible to prevent the annealing deterioration of the magneto-optical recording film and effectively prevent the coercive force of the magneto-optical recording film from decreasing.

In order to prevent the magneto-optical recording film from being degraded by annealing, the film forming temperature of the magneto-optical recording film is set to 80 ° C.
The above setting is sufficient. Therefore, if the film forming temperature of the dielectric protective film is 80 ° C. or more, it is not necessary to set the same as the film forming temperature of the magneto-optical recording film.

The upper limit of the film forming temperature for preventing the above-mentioned annealing deterioration depends on the type of the substrate material to be applied. For example, in the case of a polycarbonate substrate, the substrate is deformed when the temperature exceeds the glass transition temperature (about 120 ° C.). It is preferable that the temperature be up to about 110 ° C. because of the fear.

[0026] Here, as a material that can be applied to the substrate of the magneto-optical recording medium in the invention according to claim 1, as is conventional polycarbonate wells, epoxy resins, polyolefin resins, and the like.

The magneto-optical recording film may contain about 4 atomic% or less of Cr, Ti, or the like in order to improve environmental resistance. Further, on the dielectric protective film on the opposite side of the light beam irradiation side of the magneto-optical recording film, there is effectively formed a metal such as Al, Au, Cu or the like and an alloy film of these metals and Cr, Ti or the like. A reflective film for increasing the car rotation angle may be provided.

It is not necessary to set the substrate temperature at 80 ° C. or higher when forming this reflective film.

The substrate may be provided with guide grooves for facilitating tracking, pits used for reading signals (preformat signal pits), a ROM area, and the like.

[0030]

According to the first aspect of the present invention, after forming the substrate with a material having a higher coefficient of thermal expansion than the dielectric interference film, and forming the dielectric interference film on the substrate by sputtering. Then, the substrate is heated to 80 ° C. or more, and under this temperature condition, a magneto-optical recording film and a dielectric protective film are sequentially formed on the dielectric interference film by a sputtering method.

In the present invention, the substrate is heated to 80 ° C. or higher after forming the dielectric interference film on the substrate, and the substrate is not heated at the time of forming the dielectric interference film. Even if a substrate having a higher coefficient of thermal expansion than the above-mentioned dielectric interference film such as a polycarbonate substrate is applied, the adhesion between the substrate and the dielectric interference film formed thereon is weakened, and the stress generated therebetween is small. Value.

After forming the dielectric interference film, the substrate is heated to 80 ° C. or higher, and a magneto-optical recording film and a dielectric protection film are sequentially formed on the dielectric interference film under this temperature condition. ing. Therefore, it is possible to prevent the magneto-optical recording film from being annealed and deteriorated. Further, the coefficient of thermal expansion of the magneto-optical recording material constituting the magneto-optical recording film and containing a rare earth-transition metal alloy as a main component is a dielectric interference film. And the thermal expansion coefficient of the dielectric material constituting the dielectric protective film is higher than that between the dielectric interference film and the magneto-optical recording film and between the magneto-optical recording film and the dielectric protective film. Due to the stress caused by the difference in the rate,
Even though the substrate temperature at which the magneto-optical recording film is formed is set to 80 ° C. or higher, it is possible to prevent a decrease in the coercive force of the magneto-optical recording film by the action of the stress.

[0033]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[0034] [Example 1] dielectric interference film of silicon amorphous nitride film thickness 1200 Å (SiNx) by a sputtering method at 35-40 ° C. under conditions on polycarbonate wells made of transparent substrate 11 as shown in FIG. 1 After the transparent substrate 11 on which the dielectric interference film 21 is formed is heated to 90 ° C. by a resistance heating method, the dielectric interference film 21 is formed under this temperature condition.
A magneto-optical recording film 31 made of Tb _19.5 Fe ₇₁ Co _9.5 and having a thickness of 200 °, a dielectric protection film 41 made of amorphous silicon nitride (SiNx) having a thickness of 300 °, and a film made of Al ₉₇ Ti ₃ A 500 ° reflective film 51 was continuously formed by a sputtering method, and an overcoat layer 61 made of an ultraviolet curable resin was provided on the reflective film 51 to manufacture a magneto-optical recording medium.

As shown in FIG. 4, a magnetization curve (MH loop) indicating the relationship between the magnetization and the external magnetic field of the magneto-optical recording medium was determined. The coercive force showed a value of about 4.5 kOe, confirming that the squareness of the hysteresis loop was good.

In order to confirm the performance of this magneto-optical recording medium, a Nakamichi magneto-optical recording medium inspection apparatus (trade name: OM)
1 million E / W / R cycle tests were performed using the same method (S2000) to measure the thermal sensitivity and the magnetic field sensitivity.

The conditions of the E / W / R cycle test are as follows.

That is, the rotation speed of the recording medium is 1800 r.
pm, the measurement position on the recording medium is a part having a radius of 30 mm, and the ERASE power (erase power): 10 m
W, WRITE power (recording power): 6 mW, REA
D power (reproducing power): Irradiation conditions of 2 mW were used.

FIG. 2 shows the change in the thermal sensitivity, and FIG. 3 shows the change in the magnetic field sensitivity.

From the results shown in FIGS. 2 and 3, the magneto-optical recording medium according to the embodiment does not deteriorate in recording / reproducing characteristics even after repeating erasing, recording, and reproducing 1,000,000 times, and records data in the initial stage. It was confirmed that there was almost no difference in CNR between the signal (indicated by □ in the figure) and the signal recorded after repeating 1 million times (indicated by △ in the figure).

On the other hand, even if signal information recorded at the beginning is repeatedly reproduced one million times continuously under the condition of READ power (reproduction power): 2 mW, the CNR is reduced by 0.1.
It was only about 3 dB.

Comparative Example 1 The above-mentioned transparent substrate 1 made of polycarbonate at 35 to 40 ° C.
1 except that a dielectric interference film 21, a magneto-optical recording film 31, a dielectric protection film 41, and a reflection film 51 were successively formed in this order on FIG. A recording medium was manufactured.

As shown in FIG. 7, a magnetization curve (MH loop) indicating the relationship between the magnetization and the external magnetic field of the magneto-optical recording medium was determined. The coercive force was about 5.4 kOe, and it was confirmed that the squareness of the hysteresis loop was poor.

Then, in order to compare the performance with the magneto-optical recording medium according to the embodiment, 1,000,000 E / W / R cycle tests were performed under the same conditions as in the embodiment 1, and the thermal sensitivity and the magnetic field sensitivity were measured. . FIG. 5 shows a change in thermal sensitivity, and FIG. 6 shows a change in magnetic field sensitivity.

From the results shown in these figures, in the magneto-optical recording medium according to Comparative Example 1, the thermal sensitivity was higher than the initial state by repeating erasing, recording, and reproducing 1 million times, and the magnetic field sensitivity was also higher. The CNR of the signal recorded at the beginning (shown by □ in the figure) and the signal recorded after repeating 1 million times (shown by △ in the figure) Was also found to be significantly different.

Further, the signal information recorded at the beginning was repeatedly reproduced 1 million times continuously under the condition of READ power (reproduction power): 2 mW.
The CNR of the reproduced signal after 0.8000 times was reduced by 0.8 dB.

Comparative Example 2 The polycarbonate transparent substrate 11 was heated to 90 ° C. only under the film forming temperature conditions of the magneto-optical recording film 31, and the other dielectric interference film 21, dielectric protection film 41 and reflection film 51 were formed. The magneto-optical recording medium shown in FIG. 1 was manufactured under substantially the same conditions as in Example 1 except that films were sequentially formed at 35 to 40 ° C.

As shown in FIG. 8, a magnetization curve (MH loop) indicating the relationship between the magnetization and the external magnetic field of the manufactured magneto-optical recording medium was obtained. The coercive force showed a value of about 3.3 kOe, and it was confirmed that the squareness of the hysteresis loop was good.

Then, the signal information recorded initially using this magneto-optical recording medium was continuously and repeatedly reproduced 1 million times under the condition of READ power (reproduction power): 2 mW. Of the reproduction signal of
R was reduced by 2.1 dB, and it was confirmed that the reproduced signal was degraded.

The thermal sensitivity and the magnetic field sensitivity were measured by performing an E / W / R cycle test 1 million times under the same conditions as in Example 1. The results were almost the same as those of the magneto-optical recording medium of Example 1. was gotten.

[0051]

According to the first aspect of the present invention, the stress generated between the substrate made of a material having a higher coefficient of thermal expansion than the dielectric interference film and the dielectric interference film formed thereon is suppressed. In addition, since the magneto-optical recording film is formed in a state where the substrate is heated to 80 ° C. or higher, it is possible to prevent the magneto-optical recording film from being deteriorated by annealing. Since stress is generated between the magnetic recording film and the magneto-optical recording film and the dielectric protective film due to the difference in thermal expansion coefficient, the substrate temperature when forming the magneto-optical recording film is reduced. 80
Despite the temperature being set to not less than ° C., it is also possible to prevent a decrease in the coercive force of the magneto-optical recording film by the action of the stress.

Therefore, erasure, recording, and reproduction are continuously performed for 10 times.
The effect of being able to provide a magneto-optical recording medium in which the recording / reproducing characteristics are unlikely to be degraded even when repeated over 100,000 times, and the reproduced signal is unlikely to be degraded even when the reproduction of the recorded information is continuously repeated about 1,000,000 times. have.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a magneto-optical recording medium according to an embodiment.

FIG. 2 is a graph showing the relationship between the initial recording laser power and the CNR of the magneto-optical recording medium according to the first embodiment, and the relationship between the recording laser power and the CNR after one million E / W / R cycle tests. It is a graph which shows a relationship.

FIG. 3 is a graph showing the relationship between the initial recording magnetic field and the CNR of the magneto-optical recording medium according to the first embodiment, and FIG.
Recording magnetic field and CNR after 10,000 E / W / R cycle tests
FIG. 6 is a graph showing the relationship between

FIG. 4 is a magnetization curve (MH loop) showing the relationship between the magnetization and the external magnetic field of the magneto-optical recording medium according to the first embodiment.
FIG.

FIG. 5 is a graph showing the relationship between the initial recording laser power and the CNR of the magneto-optical recording medium according to Comparative Example 1, and the relationship between the recording laser power and the CNR after one million E / W / R cycle tests. It is a graph which shows a relationship.

6 is a graph showing the relationship between the initial recording magnetic field and the CNR of the magneto-optical recording medium according to Comparative Example 1, and FIG.
Recording magnetic field and CNR after 10,000 E / W / R cycle tests
FIG. 6 is a graph showing the relationship between

FIG. 7 is a magnetization curve (MH loop) showing the relationship between the magnetization and the external magnetic field of the magneto-optical recording medium according to Comparative Example 1.
FIG.

FIG. 8 is a magnetization curve (MH loop) showing the relationship between the magnetization and the external magnetic field of the magneto-optical recording medium according to Comparative Example 2.
FIG.

FIG. 9 is a sectional view showing the configuration of a magneto-optical recording medium according to a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transparent substrate 21 Dielectric interference film 31 Magneto-optical recording film 41 Dielectric protection film 51 Reflection film 61 Overcoat layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-62-159363 (JP, A) JP-A-6-124489 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 11/105

Claims (1)

(57) [Claims] 1. A dielectric interference film, a magneto-optical recording film formed on the dielectric interference film and mainly composed of a rare earth-transition metal alloy whose easy axis of magnetization is perpendicular to the film surface; In a method for manufacturing a magneto-optical recording medium including a dielectric protective film formed on a magnetic recording film on a substrate, the substrate is made of a material having a higher coefficient of thermal expansion than the dielectric interference film, and After forming a dielectric interference film on the substrate by sputtering, the substrate is heated to 80 ° C. or higher, and under this temperature condition, a magneto-optical recording film and a dielectric protection film are formed on the dielectric interference film by sputtering. A method for manufacturing a magneto-optical recording medium, comprising sequentially forming a film.