JP2001291291A - Method for manufacturing optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an optical recording medium having low noise and a high signal level (carrier level). SOLUTION: The optical recording medium has at least an inorganic thin film on a substrate and is used for recording and reproduction by allowing light to enter the inorganic thin film from the direction opposite to the substrate. The inorganic thin film is formed by sputtering while an AC bias voltage is applied on the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an optical recording medium used for recording information.

[0002]

2. Description of the Related Art Optical recording media can be broadly divided into a read-only type and a recordable type (including a rewritable type). The read-only type has already been put into practical use as a video disk, an audio disk, and a disk memory for a large-capacity computer. Have been. In the reproduction-only type, information data is usually recorded by a row of concave and convex pits formed on a substrate, and reproduction is performed by detecting a change in reflectance due to the presence or absence of pits. Usually, a reflective layer or the like is provided on a substrate.
Typical recordable types include a magneto-optical type, a phase change type, an organic dye type, and a perforated / deformed type.

The magneto-optical type performs recording and erasing according to the direction of magnetization of the recording layer, and performs reproduction using the magneto-optical effect. Usually, an inorganic protective layer, a magnetic layer (recording layer), a reflective layer and the like are provided on a substrate. The magneto-optical recording medium is a large-capacity, low-cost rewritable information recording medium, and includes a magneto-optical (MO) disk used for an external storage device of a computer,
It is widely used as an MD (Mini Disk) used for recording music and the like. The phase change type utilizes the fact that the reflectance or the phase of the reflected light changes before and after the phase change, and does not require an external magnetic field to detect the difference in the amount of reflected light and perform reproduction.
Usually, an inorganic protective layer, an inorganic recording layer, a reflective layer and the like are provided on a substrate. Compared to the magneto-optical type, the phase-change type is advantageous in that the drive can be easily manufactured due to the fact that a magnet is not required and the optical system is simple, and that the size and cost can be reduced. Further, there is an advantage that recording / erasing can be performed only by modulating the power of the laser beam, and one-beam overwriting, in which erasing and re-recording are performed simultaneously with a single beam, is also possible. A typical phase change recording medium is a CD-R
W (CD-Rewritable), rewritable DVD, and the like.

As the organic dye type, a recording layer made of a dye or a polymer containing the dye is used. The reflectance (refractive index) changes before and after recording, and the difference in the amount of reflected light is detected to perform reproduction. Usually, an organic dye recording layer, a reflection layer and the like are provided on a substrate. CD-R which is a typical dye type recording medium
(CD-Recordable) is now widespread. Drilling
As the deformation type, a recording layer of a low melting point metal such as Te or a dye is used, and locally heated by laser beam irradiation,
Holes or irregularities are formed. The recording methods of these optical recording media include a mode in which a transparent substrate such as a polycarbonate resin is used and light is incident on the recording layer via the substrate (substrate surface incidence method), and a method in which light is incident on the recording layer without passing through the substrate. Form (film surface incidence type). In a recording apparatus using the latter method, for example, an optical system is formed on a flying head or a contact type head, and recording and reproduction are performed by irradiating light from the recording layer side.

An advantage of the film surface incidence method is that good signal characteristics can be obtained because incident light is not subjected to distortion due to birefringence of the substrate. Further, compared to the case where the light passes through the substrate, the aberration of the light due to the disk tilt is small, and the margin for the tilt is large. Further, for the same reason, the NA (numerical aperture) of the objective lens can be increased, so that the beam spot becomes smaller and the density can be increased. By bringing the recording film and the objective lens closer to a distance of several tens of nm, near-field light recording using so-called evanescent light becomes possible. This will be described in more detail. In order to perform high-density reproduction, it is necessary to reduce the spot diameter of the reproduction light.
If the reproduction wavelength is the same, the spot diameter is inversely proportional to the NA, so that using a lens with a high NA enables high-density recording. However, when light with a high NA is incident through the substrate, there is a problem that a large aberration occurs even if the substrate has a slight inclination. This is due to the difference in the refractive index between air and the substrate. As the numerical aperture (NA) of the lens increases and the thickness of the substrate increases, the allowable range of the substrate inclination becomes significantly smaller.

In the film surface incidence method, a high NA lens can be used by irradiating light directly from a thin film surface without passing through a substrate or through a transparent resin layer having a thickness of several μm to several hundred μm. . In this method, since there is no or extremely thin layer corresponding to a conventional substrate having a refractive index different from that of air, the allowable range of the substrate inclination can be widened even if a lens with a high NA is used. SIL (Solid Imme)
rsion Lens), a remarkably high NA can be obtained. If near-field light is used, NA exceeding 1 can be obtained. In this case, since the objective lens and the medium need to be extremely close to each other, a floating head is usually used in the recording apparatus. By mounting a magnetic coil on the flying head and simultaneously generating a light beam and a magnetic field, magnetic field modulation recording can be performed on a magneto-optical recording medium, and direct overwriting becomes possible.

[0007]

In any of the above-described optical recording media, information data is arranged along a recording track, and is sequentially recorded and reproduced by a recording / reproducing system moving along the track. For recordable optical discs,
Usually, a spiral or concentric concave and convex groove is provided so that the recording / reproducing light can follow the recording track. Such an uneven groove is provided on a substrate, and a recording layer, a protective layer, a reflective layer, and the like are formed on the substrate. For forming each layer, a vacuum process such as sputtering or vacuum deposition, or application by spin coating is used. In the case of inorganic layers, usually sputtering or vacuum evaporation (electron beam evaporation, thermal evaporation, etc.)
Is used. Since dense and good film quality can be obtained, sputtering is often used.

According to the study of the present inventors, it has been found that when the same medium is reproduced by incidence on the film surface and incidence on the substrate surface, the noise on the film surface is slightly higher than that on the substrate surface. Among the reproduced signals, a noise rise is particularly large at a low frequency corresponding to a size of several μm. The reason is explained as follows. At the time of incidence on the substrate surface, the reproduction light is reflected by the thin film at the interface between the substrate and the thin film or at a position close thereto. Therefore, if the surface roughness of the substrate is small, the generation of noise due to the roughness can be extremely reduced. On the other hand, when the light is incident on the film surface, the reproduction light is reflected on the outermost surface of the film laminated on the substrate. However, the outermost surface of the film has greater roughness than the substrate surface. This may be due to the growth of film defects during film growth, which typically extends to several hundred nm during sputtering. At the incidence on the film surface, there is a problem that noise is generated at the time of reproduction due to the roughness of the film surface. Further, there is also a problem that light is scattered due to the film surface roughness, the light reflection efficiency is reduced, and the signal level is reduced.

The present invention has been made to solve this problem. An optical recording medium having a flat outermost surface even with a thick inorganic thin film, extremely low noise, and a high signal level (carrier level) has been developed. The purpose is to gain.

[0010]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a recording / reproducing method in which at least an inorganic thin film is provided on a substrate and light is incident on the inorganic thin film from a direction opposite to the substrate to perform recording or reproduction. A method for producing an optical recording medium, wherein the inorganic thin film is produced by sputtering with an AC bias applied to the substrate. In addition, the inorganic thin film referred to in the present invention is a recording layer for recording information, an inorganic protective layer such as a dielectric layer for the purpose of protecting the recording layer and improving recording / reproducing characteristics, and a reflective layer made of metal or alloy. Etc. are included. All of these inorganic thin films may be produced by sputtering with an AC bias applied to the substrate, or one or a part of the inorganic thin film may be produced as such.

In the optical recording medium manufactured by using the manufacturing method of the present invention, since the outermost surface of the thick inorganic thin film is flattened, signal noise during reproduction is significantly reduced. Further, since the light reflection efficiency is also improved, there is also an effect of increasing the signal level especially in a magneto-optical recording medium. The present invention has a great effect of applying an AC bias when the entire inorganic thin film is thick. This is because the larger the film thickness is, the more easily a film defect grows. Above all, when a reflective layer is provided, it is preferable to apply an AC bias during the formation of the reflective layer because the effects of noise reduction and reflectance improvement are large. Most of the light is reflected by the outermost surface of the reflective layer,
This is because roughness on the film surface of the reflective layer generates a particularly large noise as compared with other layers, and roughness on the film surface irregularly reflects light, thereby lowering the reflectance.

When the recording layer is an inorganic thin film, it is preferable to apply an AC bias during the formation of the recording layer because the noise reduction effect is large. This is because the roughness of the film surface of the recording layer generates large noise. In a configuration in which the recording layer is thick and the reflective layer is not provided, the degree of reflection at the recording layer is large, so that the effect is high. It is particularly preferable that the recording layer is a magnetic layer that is reproduced using the magneto-optical effect. This is because roughness on the surface of the magnetic layer leads to disturbance of magnetic anisotropy and generates large noise. The magneto-optical signal intensity can be represented by the product R · θk of the reflectance R of the magnetic layer and the Kerr rotation angle θk. That is, there is also an effect that the signal intensity is increased if the reflectance R is increased by reducing the surface roughness. Among them,
It is preferable that the recording layer includes a magnetic layer composed of a multilayer film, and a film farthest from the substrate among the magnetic layers is formed by sputtering with an AC bias applied to the substrate. This is because most of the reproduced signal is generated from the outermost magnetic film farthest from the substrate. Further, in order to further smooth the roughness of the film surface, it is preferable that the inorganic thin film is manufactured in a state where an AC bias is applied, and then the surface of the inorganic thin film is exposed to plasma (or excited gas particles) such as Ar.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. When an inorganic thin film is sputter-deposited on a substrate, once a concave or convex defect is generated, it is difficult for diagonally flying particles to enter the concave defect, while a variety of flying particles are detected in the convex defect. Adheres from different angles of incidence. Thus, concave defects grow deeper and convex defects grow higher. Therefore, even if it is a minute defect at first, the defect grows and the surface becomes rough while the film is formed up to several hundred nm. This is the process of occurrence of the roughening of the outermost surface of the film described above. Conventionally, it has been known that the roughness of the surface is reduced by exposing the film surface to plasma (or excited gas particles) such as Ar and etching after forming the thin film. If the film damage due to one collision of plasma (or excited gas particles) is sufficiently weak, the effects of the collision are averaged over the entire surface and become uniform, and the film surface can be flattened. However, the weakness of a single collision damage means that the etching rate is low. Therefore, in this method, it is difficult to remove only the defect in a thick film after the defect has grown to a large extent. If possible, very long etching is required, which is not practical. Conversely, if a strong etching is performed so that a large projection is removed in a short time, the damage of one collision is large, so that the damage is not averaged and the film surface is rather roughened. Therefore, in the plasma treatment after the film formation, defects of a thick thin film cannot be sufficiently reduced.

In the present invention, an AC bias is applied to the substrate during the formation of the thin film by sputtering. Bias is typically applied between ground and the metal substrate holder. As a result, a plasma of a sputtering gas is generated near the substrate, and the film deposited on the substrate is resputtered.
At this time, the concave defect on the film surface is difficult to be etched because the sputter gas particles flying obliquely cannot enter the inside. On the other hand, the convex defects are etched from various incident angles by the flying sputter gas particles. Therefore, the etching rate of the concave portion is low, the etching speed of the convex portion is high, and the film is flattened. As a result, the defects disappear during a short period before the growth, and finally the outermost surface of the film is significantly flattened. Using an AC bias also has the effect of making sputtered particles finer. During the flight, the particles sputtered from the target are decomposed by collision with sputter gas ions and become finer particles and reach the substrate.
As a result, variations in film thickness are reduced, and large film defects are less likely to occur. To obtain the effect as an AC bias, the frequency is preferably 10 Hz or more. More preferably, it is 30 Hz or more. If the frequency is too high, the movement of ions does not follow. Therefore, the frequency is preferably 100 MHz or less. More preferably, it is 50 MHz or less.

The maximum value of the AC bias voltage is 5
0 V or more is preferable, and 300 V or less is preferable. The input power to the substrate holder is preferably 0.1 W / cm ² or more and 1 W / cm ² or less. More preferably a 0.15 W / cm ² or more, and 0.7 cm ² or less. Substrate etching of sputter gas particles also occurs by applying a negative DC bias instead of an AC bias to the substrate. However, in the case of a DC bias, most of the sputter gas particles enter the substrate in a direction perpendicular to the substrate according to the electric field distribution. For this reason, the effect of preferentially shaving the above-mentioned convex portion is small. Depending on conditions, there is a possibility that the surface may be roughened. In the case of an AC bias, the direction of the sputter gas ions changes with the time change of the electric field. For this reason, collisions between ions easily occur, and the sputtering gas particles enter the substrate from all directions. Therefore, the effect of preferentially removing the convex portion is great.

When the substrate is made of a nonconductive material such as resin or glass, if a direct current bias is applied, the attracted positive charges accumulate on the substrate surface, so that the effect of the bias is immediately lost. With an AC bias, the potential swings positively and negatively, so that the accumulated positive charges are canceled by the electrons. Therefore, by using the AC bias, any substrate including not only a conductor but also a nonconductor can be used.
Note that a negative DC bias may be superimposed on the AC bias. This is more preferable because more ions of the sputtering gas having a positive charge enter the substrate and enhance the etching effect. Briefly, by inserting a capacitor in series between the power supply (and the matching circuit) and the substrate holder, a negative self bias can be obtained. Of course, a DC voltage can be superimposed on the power supply side.
The superimposed negative potential is preferably 20 V or more, more preferably 40 V or more. If the voltage is too low, the effect is small. The negative potential is preferably 200 V or lower, more preferably 150 V or lower. If the voltage is too high, the effect as an AC bias is reduced. When the substrate is non-conductive, it is preferable that the maximum AC voltage is higher than the DC voltage on which the AC voltage is superimposed in order to cancel the accumulation of the positive charges by the electrons.

As a sputtering gas, an inert gas can be used. For example, Ar, Xe, Kr, and Ne are used.
Ar is most preferably used in terms of sputtering efficiency and cost. In the production of the dielectric layer, etc., the inert gas is oxygen,
Reactive sputtering may be performed by mixing nitrogen, hydrogen, and the like. As a sputtering method when using an AC bias, high-frequency sputtering and DC sputtering can be used. For DC sputtering,
It is more preferable that the high-energy sputtering gas particles rebounding from the target have an effect of etching the film. In order to increase the energy of the rebound, it is preferable that the input power at the time of performing the sputtering be 400 W or more for a 5-inch target. More preferably, it is 500 W or more. However, if it is too large, there are problems such as heating of the substrate and cracking of the target. More preferably, it is 1.2 kW or less.
When a target of another size is used, the input power may be changed in proportion to the area. Further, after the inorganic thin film is manufactured with an AC bias applied, the surface of the inorganic thin film is exposed to plasma (or excited gas particles) such as Ar,
The roughness of the film surface can be further smoothed. By preparing the inorganic thin film in this manner, the film surface becomes flat, and the average roughness Ra of the outermost surface of the inorganic thin film is 0.9 nm.
The following optical recording medium can be obtained. It is more preferably 0.8 nm or less. The maximum roughness Rmax is preferably set to 10 nm or less. More preferably, it is 8 nm or less. Here, Ra and Rmax are values when the surface is measured by an atomic force microscope (AFM).

The present invention is preferably used for producing a magneto-optical recording medium and a phase change recording medium. The configuration of the magneto-optical recording medium is usually a substrate / inorganic protective layer / recording layer / inorganic protective layer, or a substrate / reflective layer / inorganic protective layer / recording layer / inorganic protective layer,
It is. The structure of the phase change recording medium is usually a substrate / reflective layer /
Inorganic protective layer / recording layer / inorganic protective layer. Each layer may be composed of a plurality of films. Further, another film may be further formed as necessary. As the substrate, a substrate obtained by injection molding a resin such as polycarbonate or PMMA using a stamper having irregularities is preferable from the viewpoint of cost and productivity.
There is also a method in which an ultraviolet-curing resin, a thermosetting resin, or the like is applied on glass, metal, or the like, and the resin is cured with a stamper adhered thereto. Alternatively, a method of casting a metal such as glass or an aluminum alloy can also be used.

The concavities and convexities formed on the substrate by such a method include those representing recording data, those for generating a servo signal for following a recording track, those showing an address of a recording area, and those for reproducing a clock. There are things to generate. The servo signal can be generated by a method of generating a continuous groove (continuous groove method) or a method of generating a servo signal from pits formed at intervals (sample servo method). Alternatively, a substrate without the above unevenness may be used. As the recording layer of the magneto-optical recording medium,
Any magnetic layer that can be reproduced using the magneto-optical effect may be used.
For example, TbFe, TbFeCo, TbCo, GdFeC
o, an amorphous magnetic film of a rare earth such as DyTbFeCo and a transition metal, a polycrystalline perpendicular magnetic film such as MnBi or MnCuBi, or a Pt / Co multilayer film is used. The magneto-optical recording layer may be a single layer, or two or more magnetic layers such as GdTbFe / TbFe may be used in order to enable overwriting and super-resolution. The recording layer configuration of the medium using the super-resolution technique will be described later in detail.

The recording layer of the phase-change recording medium may be any material whose reflectivity changes depending on the crystal state. Examples thereof include GeSbTe, InSbTe, and AgSbT.
Compounds such as e, AgInSbTe and InGeSbTe can be used. The material of the inorganic protective layer is determined in consideration of thermal conductivity, chemical stability, mechanical strength, adhesion, refractive index, and the like. Generally, a dielectric can be used. A simple substance such as Si oxide, Al oxide, Ta oxide, Ti oxide, Si nitride, Al nitride, Si carbide, or a mixture thereof is preferably used. In particular, Si nitride, Si oxide, T oxide
a, ZnS—SiO _{2 and the} like are preferable. The reflection layer is made of a metal or an alloy.
Metals such as Ag, Cu, Au, and Pt or alloys containing these as main components can be used. The high reflectance is, for example, a reflectance of 90% or more.

When a flying head is used for recording and reproduction, a hard layer such as a carbon film, a hydrogenated carbon film and a nitrogenated carbon film may be provided on the outermost surface. Particularly, a hydrogenated carbon film is preferable. The hydrogenated carbon film may be any film containing hydrogen and carbon, for example, using a carbon target,
It can be formed by sputtering in a plasma containing a sputtering gas and a hydrogen gas. The content of hydrogen in the sputtering atmosphere is usually 2 to 20% by volume. When a flying head is used, it is preferable to further apply a lubricant thereon. As a lubricant, perfluoropolyether having an ester bond, dialkylamide carboxylic acid, perchloropolyether, stearic acid,
Sodium stearate, phosphate esters and the like are preferred. The ester bond may be located anywhere in the molecule, but it is more preferable to have an ester bond functional group at the end, since the movable portion in the molecule becomes longer and lubricity is easily obtained. Particularly -C _a F _2a O- units (wherein, a is an integer of 1 to 4) in the main chain has a perfluoropolyether having a functional group of the terminal ester bond.

For example, Fomblin manufactured by Ausimont Co., Ltd.
-Z-DEAL is a polymer of CF ₂ CF ₂ O and CF ₂ O and has a linear structure, and has an ester group —COOR (both in which
R represents an alkyl group which may be substituted by fluorine. ). In addition, demnum manufactured by Daikin Industries, Ltd.
The type (SP or SY) is a homopolymer of hexafluoropropylene oxide, and has an ester group -CO at one end.
OR (where R represents an alkyl group which may be substituted with fluorine). The molecular weight of the lubricant is 100-1
It is preferably in the range of 0000. If the molecular weight is low, the vapor pressure is generally high, evaporates little by little after coating, and moves away from the desired film thickness with time. Conversely, when the molecular weight is high, the viscosity is generally high, and the desired lubricity may not be obtained.

Examples of the solvent for dissolving them include chlorofluorocarbons, alcohols, hydrocarbons, ketones, and the like.
Ether type, fluorine type, aromatic type and the like are used. The coating thickness of the lubricant is preferably in the range of 1 to 20 nm. If the thickness is out of this range, that is, if the thickness is too small, desired lubricity cannot be obtained, but even if the thickness is too large, a certain level of lubricity cannot be obtained, and excess lubricant moves to the outer peripheral side with rotation of the disk. The film thickness distribution in the periphery is likely to occur. A transparent organic thin film may be provided as a protective film on the inorganic thin film. The organic protective layer has an effect of protecting the recording film from damage and corrosion. There are a method of applying an ultraviolet curable resin and a thermosetting resin by spin coating or a dipping method, followed by curing, and a method of bonding a resin sheet. The thickness of the organic thin film is 1μ
m or more, and preferably 200 μm or less.
More preferably, it is 3 μm or more and 150 μm or less. When a flying head is used and it is necessary to bring the head close to the recording film by about 1 μm or less, the thickness of the protective film becomes extremely thin. At this time, since the organic thin film does not have enough hardness,
It is preferable to use a high hardness inorganic protective film on the outermost surface. Preferred is hydrogenated carbon. Further, it is preferable to apply a lubricant thereon.

Hereinafter, preferred embodiments of the present invention will be described. In the present invention, the effect of applying an AC bias is great when the entire inorganic thin film is thick. This is because the larger the film thickness is, the more easily a film defect grows. Therefore, the effect is great when used for manufacturing a medium in which the total thickness of the inorganic thin film is 100 nm or more. More preferably, it is 150 nm or more.
However, considering the productivity of the medium, the total film thickness is 500 nm.
It is preferred that: From the viewpoint of noise reduction, it is most preferable to apply an AC bias to all the inorganic thin film layers. However, if this causes a problem in the recording / reproducing characteristics, it may be applied to only some of the layers. When an AC bias is applied to only some of the layers, the thickness of the layer is 20 n
The effect is great when used for a layer with a thickness of at least m. More preferably, the film thickness is 25 nm or more. This is because the effect of noise reduction disappears when the film thickness to which the AC bias is applied is too thin.

When the inorganic thin film includes a reflective layer made of a metal or an alloy, the reflective layer is preferably formed by sputtering with an AC bias applied to the substrate. If a reflective layer is provided between the recording layer and the substrate, most of the light will be reflected on the outermost surface of the reflective layer, so that the rough surface of the reflective layer will generate a particularly large noise compared to other layers. I do. In addition, the roughness of the film surface irregularly reflects light, so that the reflectance is reduced. As a result, the performance as a reflective layer that reflects light to improve the reproduction characteristics by the interference effect deteriorates.

Therefore, it is preferable to apply an AC bias at least when forming the reflective layer. The effect is particularly large when the thickness of the reflective layer is large. In a phase-change medium, the thickness of the reflective layer tends to be increased to assist thermal diffusion from the recording layer. When the thickness of the reflective layer is 100 nm or more, the surface is extremely rough, and the increase in noise is large. Therefore, 100
It is highly effective when used for manufacturing a medium having a reflective layer of nm or more. However, the thickness is preferably 500 nm or less. Since the reflective layer has a high thermal conductivity, if it is too thick, the laser power required for recording becomes extremely large.
Further, in a configuration in which the thickness of the recording layer is as thin as 50 nm or less and most of the reproduction light reaches the reflective layer, the effect is higher.
More preferably, the recording layer has a thickness of 40 nm or less. However,
8 nm or more. If the recording layer is too thin, the reproduced signal will be significantly reduced.

The present invention is particularly effective when a metal or alloy mainly composed of Al or Ag is used for the reflective layer. This is because the reflective layer mainly composed of Al or Ag has large crystal grains and easily causes surface roughness. Al or Ag is used as the reflection layer.
In order to control thermal conductivity or suppress corrosion, use Si, C
It is preferable to add r, Ta, Ti, Pt, Mo, B, and the like in an amount of 10 atomic% or less. When the inorganic thin film includes a magnetic layer reproduced by using the magneto-optical effect, it is preferable that at least a part of the magnetic layer is formed by sputtering with an AC bias applied to the substrate. When the magnetic layer is composed of a multilayer film, it is more preferable that at least a film farthest from the substrate among the multilayer films is formed by sputtering with an AC bias applied to the substrate. This is because roughness on the surface of the magnetic layer leads to disturbance of magnetic anisotropy, and particularly large noise is generated. The magneto-optical signal intensity can be represented by the product R · θk of the reflectance R of the magnetic layer and the Kerr rotation angle θk. That is, there is also an effect that the signal intensity is increased if the reflectance R is increased by reducing the surface roughness.

When the recording layer is composed of a multilayer magnetic film such as a magnetically induced super resolution (MSR) medium, at least a film farthest from the substrate is formed by sputtering with an AC bias applied to the substrate. Is preferred. This is because most of the reproduced signal is generated from the outermost magnetic film farthest from the substrate. If the roughness of the outermost surface of the magnetic layer is small, the noise reduction effect is remarkable. Here, the super-resolution (Ma
gnetically induced super resolution (MSR)
The medium using the technology will be described in detail. This method is
It basically consists of a layer on which information is recorded (recording magnetic layer) and a layer for reproducing information (reproducing magnetic layer). Recording is performed on the recording layer, and the magnetization direction of the recording layer is transferred to the reproducing layer during reproduction. And read. Usually, the state of transfer to the reproducing layer is controlled by the heating temperature of the recording layer. According to this method, it is possible to reduce the interference of the waveform of the reproduced signal by utilizing the temperature distribution in the reproduction light spot and deforming the magnetic domain of the reproduction layer by the temperature distribution, thereby improving the quality of the high-density recording information. Can be played well.

There are various forms of the MSR.
For example, an "exchange coupling CAD" system,
As shown in No. 29, "Inverted MSR" uses a medium consisting of three layers exchange-coupled to each other: a reproducing layer having a low coercive force, a cutting layer having a low Curie temperature, and a recording layer having a high Curie temperature and a large coercive force. Method, JP-A-8-2218
No. 18, "Magnetostatic coupling CAD" system in which a nonmagnetic blocking layer is provided between a recording layer and a reproducing layer and the magnetization direction of the recording layer is transferred to the reproducing layer only by the magnetostatic coupling force. The latter two are collectively called magnetostatically coupled MSRs.

Hereinafter, the layer configuration of the magnetostatic coupling type MSR will be described as an example. In the inversion type MSR system and the magnetostatic coupling CAD system, the reproducing layer preferably has a composition in which rare earth metal magnetization is dominant. In the reversal type MSR, this is an essential condition for reversing the directions of the exchange coupling force and the magnetostatic coupling force. Further, in the magnetostatic coupling CAD system, it is an essential condition that the film is an in-plane magnetic film at a low temperature and changes to a perpendicular magnetic film due to a decrease in magnetization at a high temperature. Materials used for the reproducing layer include GdFeCo, GdCo, GdFe, and GdDyF.
e, GdDyCo, GdDyFeCo, GdTbFe,
GdTbCo, GdTbFeCo, DyFeCo, Dy
Co, TbCo, TbFeCo, TbDyFeCo, T
An alloy of a rare earth metal such as bDyCo and a transition metal is used. Among them, it is preferable to use an alloy containing Gd from the viewpoint of the Curie temperature and the coercive force. Particularly preferred is Gd
FeCo and GdFe. Curie temperature is 2
It is preferably at least 50 ° C.

A magnetic material such as PtCo or a superlattice of Pt and Co can be laminated on the reproducing layer. Since these have a large Kerr rotation angle at a short wavelength, they can be applied to a high-density recording medium using a blue laser or the like. In order to increase the perpendicular magnetic anisotropy of the reproducing layer, it is preferable to apply a certain film stress to the magnetic layer to generate anisotropy by the inverse magnetostriction effect. It is preferable because it stands upright. It is preferably at most 100 nm, more preferably at most 70 nm, particularly preferably at most 60 nm. However, if it is too thin, the leakage magnetic flux becomes small and the magnetostatic coupling force decreases, so it is preferably at least 10 nm, more preferably at least 15 nm, particularly preferably at least 20 nm.

A cutting layer for cutting exchange coupling is provided between the reproducing layer and the recording layer. In the inversion type MSR system, the cutting layer is a layer having a lower Curie temperature than the recording layer and the reproducing layer, and blocks exchange coupling at a high temperature exceeding the Curie temperature. In the magnetostatic coupling CAD method, a non-magnetic film is mainly used so as to block exchange coupling in all temperature regions. In the inversion type MSR method, a cutting layer having a lower Curie temperature than the reproducing layer and the recording layer is used. The Curie temperature of the cutting layer is preferably about 90 to 180 ° C. If the Curie temperature is too low, the signal from the exchange-coupled area (low-temperature area in the reproduction light spot) becomes small, while if the Curie temperature is too high, high reproduction power and high recording power are required.

The inversion type MSR cutting layer preferably has a high perpendicular magnetic anisotropy and generates a strong force in the magnetization of the reproducing layer. Materials used for the cutting layer include TbFe,
TbFeCo, DyFeCo, DyFe, TbDyFe
An alloy of a rare earth such as Co and a transition metal is preferable. The film thickness is 2
nm or more and preferably 30 nm or less. If it is thin, it is difficult for the exchange coupling to be sufficiently interrupted, and if it is thick, the magnetic flux of the magnetostatic coupling does not easily reach. In the magnetostatic coupling CAD, a nonmagnetic or paramagnetic material such as a metal or a dielectric is preferably used at a temperature at which a magnetization direction is transferred to at least the reproducing layer. For example, Al, Ta, Cr, Ti,
W, Si, Pt, Cu, Tb, Gd, Dy, ZnS, S
i ₃ Si nitride such as N _4, AlN, TiN, carbon, a carbon hydride or the like. A mixture of these may be used. However, those having high magnetic permeability, such as Fe and Ni, are not preferable because they impede the transmission of magnetic flux from the recording layer to the reproducing layer and reduce the magnetostatic coupling. The film thickness is 2 nm or more, and 3
Preferably, the thickness is 0 nm or less. If it is too thin, it is difficult to sufficiently shut off the exchange coupling, and if it is too thick, the magnetic flux of the magnetostatic coupling does not easily reach.

Since the recording layer is a layer that stores records,
It is necessary to have a Curie temperature as high as not to be deteriorated by heating by the reproduction light and to be able to stably hold the minute magnetic domain. The recording layer needs to have a Curie temperature that does not deteriorate by heating by the reproduction light. It is also preferable that the recording layer has a high perpendicular magnetic anisotropy in order to stably maintain the recording magnetic domain. The recording layer may be a single film, but a plurality of recording films is also a preferred embodiment. In the case of a plurality of recording films, each recording film needs to have a Curie temperature large enough not to be degraded by heating by the reproduction light, and to have a high perpendicular magnetic anisotropy in a stable manner. It is preferable to keep the recording magnetic domains. Preferably, the recording films are exchange-coupled to each other.
In the case of a combination of a film having a low coercive force (for example, GdFeCo) and a film having a high coercive force (for example, TbFeCo), if the film is recorded on the high coercive force film, it is transferred to the low coercive force film by the exchange coupling force.

When the first recording film, the second recording film,... Are arranged in the order of proximity to the reproducing layer, a layer having a magnetization direction to be used for magnetostatic coupling is arranged on the first recording film. It is preferable to arrange them. This is because the layer closest to the reproducing layer exerts the magnetostatic coupling force most efficiently. By providing a layer having a large magnetization as the first recording film and providing a layer having a smaller magnetization but a larger coercive force than the first recording film as the second recording film, the minute magnetic domains can be stably recorded while maintaining a strong magnetostatic coupling force. it can. In the case of the inversion type MSR, it is preferable that the first recording film has the transition metal magnetization dominance at room temperature because it is desired to couple the magnetization of the opposite transition metal dominant magnetization to the reproducing layer in which the rare earth metal magnetization is dominant. . In magnetostatic coupling CAD, the recording layer may be either rare-earth-metal-dominated (RE-rich) or transition-metal-dominated (TM-rich). Therefore, it is preferable that the recording layer has transition metal magnetization dominance at room temperature. When the recording layer is composed of a plurality of recording films, the magnetization direction of the recording layer refers to the magnetization direction derived from the direction of the magnetostatic coupling force exerted on the reproduction layer by the recording layer as a whole.

For example, when the magnetization direction is transferred to the RE-rich reproducing layer, the recording layer is RE-rich if the sub-lattice magnetizations of the reproducing layer and the recording layer are aligned, and T is reversed if the sub-lattice magnetization is reversed.
It can be determined that it is M rich. The number of recording films in the recording layer may be three or more, but is preferably two or less in terms of simplicity in production. As a substance forming the recording layer, it is preferable that at least one recording film has a high coercive force and can stably store recordings. As this high coercive force film, T
bFeCo, TbCo, DyFeCo, TbDyFeC
o, GdTbFe, GdTbFeCo and the like are preferably used. Among them, TbFeCo has high perpendicular magnetic anisotropy,
It is particularly preferable because of its large coercive force. The coercive force is preferably at least 5 kOe. As long as the films other than the high coercive force film are exchange-coupled to the high coercive force film, they may have a small coercive force alone. For example, GdFe, GdFeCo, G
dCo.

When the recording layer is thin, it is difficult to transfer the magnetic domain direction to the control layer stably. Therefore, the thickness of the recording layer is preferably 20 nm or more, more preferably 25 nm or more. On the other hand, if the recording layer is thick, sensitivity and productivity tend to deteriorate, so the thickness of the recording layer is preferably 100 nm or less, more preferably 70 nm or less. When the recording layer is composed of a plurality of recording films, the thickness of each recording film is preferably set in the above range. If the Curie temperature of the recording layer is low, the power margin for reproduction is lost or narrowed. More preferably, it is 250 ° C. or higher. However, if the temperature is too high, the laser power required for recording becomes extremely large.

When the recording layer comprises a plurality of recording films, the Curie temperature of the recording film having the lowest Curie temperature is set in the above range. When simply called the “Curie temperature of the recording layer”,
It refers to this lowest Curie temperature. When the recording layer is a combination of the low coercive force film having a high Curie temperature as the first recording film and the high coercive force film having a lower Curie temperature as the second recording film, when reproducing, This is a particularly preferable mode because even when the temperature rises to near the Curie temperature, strong magnetostatic coupling can be obtained without lowering the magnetization of the first recording film. In this case, specifically, Gd is used as the first recording film.
FeCo and TbFeCo are preferably used as the second recording film. When the recording layer is a single layer, T
It is preferable to use bFeCo. When the magnetization of each of the recording films is too large, the read signal characteristics deteriorate due to a decrease in perpendicular magnetic anisotropy. Therefore, it is not preferable to use a composition far from the compensation composition for the recording layer.

Therefore, the rare earth metal content in the recording layer is preferably at least 18 at%, more preferably at least 19 at%, particularly preferably at least 20 at%. Alternatively, the content of the rare earth metal in the recording layer is preferably 32% by atom or less, more preferably 31% by atom or less, and particularly preferably 30% by atom or less. Note that in this specification, atomic% is used for all compositions. When TbFeCo is used as a high coercivity recording film in the recording layer, C in FeCo
The ratio of o is preferably 10% or more and 40% or less for obtaining an appropriate Curie temperature. If the magnetization of the recording layer is too large, magnetization reversal due to a leakage magnetic field is likely to occur. Therefore, the magnetization of the recording layer is preferably 250 emu / cc or less at room temperature. More preferably, it is 200 emu / cc or less. If the magnetization of the recording layer at room temperature is too small, the magnetostatic coupling force becomes small even at a high temperature, so that it is preferably 50 emu / cc or more. More preferably, it is 100 emu / cc or more.

In order to generate the magnetostatic coupling force more reliably,
On the side of the recording magnetic layer opposite to the reproducing magnetic layer, a layer having a higher magnetic permeability than the recording magnetic layer, for example, Fe, Ni, Co, FeN
i, AlSiFe, etc. directly or through a non-magnetic layer.
It may be provided about 0 to 50 nm. Due to the effect of these layers, the leakage magnetic flux of the recording magnetic layer is more efficiently generated and coupled to the reproducing magnetic layer. If it is in direct contact with the recording magnetic layer, the perpendicular magnetic anisotropy of the recording magnetic layer is reduced.

[0041]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. (Examples 1 to 4, Comparative Example 1: Magneto-optical recording medium) The substrate thickness is 1.2 mm, the interval between the grooves is 1.4 μm, the flat portion between the grooves is 0.6 μm, and the groove width is 0. A polycarbonate substrate with a diameter of 130 mm for land and groove recording having a groove having a trapezoidal cross section with a groove depth of 67 nm and a groove depth of 60 nm was prepared. This substrate is introduced into a sputtering device,
Evacuation was performed to a degree of vacuum of 3 × 10 ⁻⁷ Torr or less. The targets used for sputtering were all 5 inches in diameter. 80 ccm of Ar as a sputtering gas, O ₂
At 25 mcm and the pressure at 3.5 mTorr.
A first dielectric layer of Ta oxide having a thickness of 70 nm was formed by direct current reactive sputtering of a 00 W Ta target.

Next, Ar was set to 80 ccm and the pressure was set to 3 mTorr.
As a result, a recording layer made of Tb ₂₁ (Fe ₈₀ Co ₂₀ ) _{79 having a} thickness of 100 nm was produced by direct current sputtering of an 800 W TbFeCo alloy. Subsequently, Ar was set to 80 ccm and N
₂ at a flow rate of ₂₀ ccm and a pressure of 3.2 mTorr,
A second dielectric layer made of Si nitride having a thickness of 70 nm was formed by DC reactive sputtering of a 500 W Si target (Comparative Example 1). Next, as shown in Table 1, a frequency of 13.56 MH was used when all or each layer was formed.
z, amplitude 160V, self bias 70V, power 200
AC bias of W is 300 mm in diameter with the substrate mounted
(Examples 1 to 4).

Table 1 shows the results of AFM measurement of the average roughness (Ra) of the outermost surface of the inorganic thin film of the magneto-optical disk manufactured as described above. These magneto-optical disks are set to a wavelength of 6
It was rotated at a linear velocity of 8 m / s by an optical disk evaluation machine equipped with an optical head having an optical head of 80 nm and NA = 0.55, and evaluation was performed by film surface incidence. First, a magnetic field of 300 Oe and an erasing power of 7
Erasing was performed at mW, and noise was measured at the mirror surface where no groove was formed. Next, after similarly erasing in the groove, the magnetic field 3
00 Oe, recording power 8 mW, recording frequency 2 MHz (corresponding to mark recording with a mark length of 2 μm), light emission duty
Recording was performed at 35% and then reproduced. The reproduction power was 2.5 mW. Table 1 shows the noise of the reproduced signal at the mirror surface and the CNR at the groove. Although the effect of the AC bias was recognized in all the layers, the noise was most greatly reduced by applying the AC bias when the recording layer was formed. In Examples 1 and 3 in which a bias was applied during the formation of the recording layer, the carrier level also increased by about 1 dB. Further, 0 to 10M in the mirror surface portion of Comparative Example 1 and Example 1
The difference in the noise spectrum at Hz is shown in FIG. The resolution bandwidth (Resolution Band Width) is 30 kHz, and the video bandwidth (Video Band Width) is 10 kHz.

[0044]

[Table 1]

(Examples 5 to 7, Comparative Examples 2 to 4: Magneto-optical recording medium provided with a reflective layer) Using the same substrate and film forming conditions as in Example 1, 80 cc of Ar was used as a sputtering gas.
Al ₉₈ Ta _{2 at} a pressure of 3.0 mTorr.
As shown in Table 2, film thicknesses of 80, 130, and 180 nm were formed. Next, Ar is 80c
cm, ₂₀ ccm of N ₂ and a pressure of 3.2 mTorr
The first dielectric layer made of Si nitride having a thickness of 30 nm was formed by reactive sputtering. Then, Ar was set to 80 nm and the pressure was set to 3 mTorr.
A recording layer made of b ₂₁ (Fe ₈₀ Co ₂₀ ) ₇₉ was produced. Subsequently, a second protective layer made of Si nitride having a film thickness of 80 nm was formed by reactive sputtering at a pressure of 3.2 mTorr by flowing Ar at 80 ccm and N ₂ at 20 ccm (Comparative Examples 2 to 4).

Next, when forming the reflective layer, the frequency was 13.56M.
Hz, amplitude 160V, self-bias 70V, power 20
0W AC bias, 300m diameter with substrate mounted
In addition, a film was formed on a stainless steel substrate holder. (Examples 5 to 7) Table 2 shows the average roughness (Ra) of the outermost surface of the inorganic thin film of the magneto-optical disk manufactured as described above, which was measured by AFM.
Shown in These magneto-optical disks were evaluated under the same conditions. Table 2 shows the results.

[0047]

[Table 2]

Example 8, Comparative Example 5: Phase Change Recording Medium
Using the same substrate and film forming conditions as in Example 1, 80 ccm of Ar was flowed as a sputtering gas, and the pressure was 3.0 m.
A reflective layer made of Al ₉₈ Ta ₂ having a thickness of 150 nm was formed as Torr. Next, Ar was flowed at 80 ccm, the pressure was set to 3 mTorr, and the film thickness was 3 by high frequency sputtering.
A first dielectric layer made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ having a thickness of 0 nm was formed. Subsequently, Ar was set to 80 ccm and the pressure was set to 3 m.
A recording layer made of GeSbTe having a film thickness of 25 nm as Torr was formed. Subsequently, a second protective layer made of (ZnS) ₈₀ (SiO ₂ ) _{20 having a} film thickness of 80 nm was formed by high-frequency sputtering with Ar flowing at 80 ccm and a pressure of 3 mTorr (Comparative Example 5).

Next, at the time of forming the reflective layer, the frequency was 13.56.
MHz, amplitude 160V, self bias 70V, power 2
An AC bias of 00 W is applied to the substrate with a diameter of 300
The film was formed on a stainless steel substrate holder having a thickness of 2 mm. Otherwise, a film was formed in the same manner as in Comparative Example 5. (Example 8). When the average roughness (Ra) of the outermost surface of the inorganic thin film of the phase change disk manufactured as described above was measured by AFM, Example 8 was 0.63 nm and Comparative Example 5 was 0.91 nm. These phase-change disks were manufactured at a wavelength of 680 nm and an NA of
Rotation was performed at a linear velocity of 8 m / s by an optical disk evaluation machine equipped with an optical head of 0.55, and evaluation was performed by film surface incidence. Erasing was performed with an erasing power of 7 mW, and noise was measured at a mirror surface where no groove was formed. Next, after similarly erasing in the groove, the recording power was 14 mW, the recording frequency was 4 MHz.
(Corresponding to mark recording with a mark length of 1 μm), light emission du
Recording was performed at a ty of 35%, and reproduction was performed at a reproduction power of 2.5 mW. The noise at the mirror surface was −73.2 dBm in Comparative Example 5.
And Example 8 was −77.8 dBm. CNR
Is 51.2 dB for Comparative Example 5 and 54.6 dB for Example 8.
dB.

(Examples 9 to 11, Comparative Example 6: Multilayer magneto-optical recording medium) Using the same substrate and film forming conditions as in Example 1,
80 ccm of Ar and ₂ of O ₂ as sputtering gas
5 ccm, 500 mTorr pressure and 500 mTorr
A first dielectric layer made of Ta oxide having a thickness of 70 nm was formed by direct current reactive sputtering of a W Ta target. Then, 3 mTorr to 80ccm pressure Ar, a recording layer composed of _{Tb 22 (Fe 80 Co 20)} 78 with a thickness of 60nm by a DC sputtering TbFeCo alloy as a power 800 W, film thickness 10nm by a DC sputtering TbFeCo alloy Tb ₂₁ A cut layer made of (Fe ₉₂ Co ₈ ) ₇₉ and a readout layer made of Gd ₃₅ (Fe ₈₀ Co ₂₀ ) _{65 having a} thickness of 25 nm were formed by direct current sputtering of Gd and FeCo.

Subsequently, Ar was 80 ccm and N ₂ was 20 cc.
m and the pressure to 3.2 mTorr, 500W S
Film thickness 7 by DC reactive sputtering of i target
A second dielectric layer made of 0 nm Si nitride was formed (Comparative Example 6). Thus, an inversion type magnetic super-resolution medium was manufactured. Next, as shown in Table 3, when all or each of the layers was formed, the frequency was 13.56 MHz and the amplitude was 160.
V, a self-bias of 70 V, and an AC bias of 200 W of power were applied to a stainless steel substrate holder having a diameter of 300 mm on which the substrate was mounted to form a film (Examples 9 to 11). Table 3 shows the results of AFM measurement of the average roughness (Ra) of the outermost surface of the inorganic thin film of the magneto-optical disk manufactured as described above. These magneto-optical disks were evaluated under the same conditions. The results are shown in Table-3. Although the effect of the AC bias was recognized in all the layers, it can be seen that the noise was reduced most greatly by applying the AC bias when forming the reproducing layer, which is the uppermost layer of the magnetic layer.

[0052]

[Table 3]

(Example 12: Plasma exposure) After a reflective layer was formed in the same manner as in Example 6, Ar was flowed at 80 ccm.
The reflective layer surface was exposed to plasma for 10 minutes by applying an AC voltage to the substrate at a pressure of 3.0 mTorr and applying the same AC voltage as in the film formation and discharging the substrate. Table 2 shows the results of AFM measurement of the average roughness (Ra) of the outermost surface of the inorganic thin film of the magneto-optical disk manufactured as described above. These magneto-optical disks were evaluated under the same conditions. Table 2 shows the results. Ra was further improved than in Example 6, noise was reduced, and the groove CNR was increased. (Example 13, Comparative Example 7: Magneto-optical recording medium provided with Ag reflective layer) A magneto-optical disk was produced in the same manner as in Comparative Example 2 except that a reflective layer made of Ag was used as the reflective layer (Comparative Example). 7). Next, when forming the reflective layer, the frequency is 13.56.
MHz, amplitude 160V, self bias 70V, power 2
An AC bias of 00 W is applied to the substrate with a diameter of 300
(Example 13) Table 2 shows the results of AFM measurement of the average roughness (Ra) of the outermost surface of the inorganic thin film of the magneto-optical disk manufactured as described above. These magneto-optical disks were evaluated under the same conditions. Table 2 shows the results. In Example 13, Ra was improved compared with Comparative Example 7, noise was reduced, and the groove CN
R increased. Since the Ag reflection layer originally has a large surface roughness, the manufacturing method of the present invention has a large improvement effect.

[0054]

According to the optical recording medium manufactured by the method of the present invention, the outermost surface of the thick inorganic thin film is flattened. Is significantly reduced. Further, since the light reflection efficiency is also improved, there is also an effect of increasing the signal level especially in a magneto-optical recording medium.

[Brief description of the drawings]

FIG. 1 is a diagram showing a difference in noise spectrum depending on the presence or absence of an AC bias during film formation.

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Claims (5)

[Claims] 1. A method for producing an optical recording medium, comprising: at least an inorganic thin film on a substrate; and recording or reproducing by recording light by irradiating the inorganic thin film with light from a direction opposite to the substrate. A method for producing an optical recording medium, wherein the inorganic thin film is produced by sputtering with an AC bias applied to the substrate. 2. The method for manufacturing an optical recording medium according to claim 1, wherein the inorganic thin film includes a reflective layer made of a metal or an alloy, and the reflective layer is formed by sputtering with an AC bias applied to the substrate. . 3. The method according to claim 1, wherein the inorganic thin film includes a recording layer on which recording is performed using light, and the recording layer is formed by sputtering with an AC bias applied to the substrate.
3. The method for producing an optical recording medium according to claim 1. 4. The magnetic recording medium according to claim 3, wherein the recording layer is a magnetic layer reproduced by using a magneto-optical effect, and the magnetic layer is formed by sputtering with an AC bias applied to the substrate.
3. The method for producing an optical recording medium according to claim 1. 5. The recording layer includes a magnetic layer comprising a multilayer film, and a film of the magnetic layer farthest from the substrate is formed by sputtering with an AC bias applied to the substrate. 3. The method for producing an optical recording medium according to claim 1.