JP2006179156A - Magneto optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magneto optical recording medium in which domain wall displacement is reproduced with appropriate stability and crosswrite characteristics between adjoining tracks are also appropriate because there is a case that a domain wall displacement phenomenon is not reproduced with appropriate stability in a conventional magnetic optical recording medium utilizing the domain wall displacement. <P>SOLUTION: The magneto optical recording medium in which a land and a groove are formed and the domain wall displacement is used is, when the inclined surface of the land is divided into an upper part and a lower part, the magneto optical recording medium in which the surface roughness Ra 1 of the upper surface and the surface roughness Ra 2 of the lower surface are in a relationship of Ra1<Ra2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magneto-optical recording medium that records and reproduces information by laser light using a magneto-optical effect, and more particularly to a method for further increasing the density of a magneto-optical recording medium that utilizes movement of a domain wall during reproduction. .

  A magneto-optical recording medium is attracting attention as a rewritable high-density recording medium. In addition, in order to obtain a large-capacity recording medium, there is an increasing demand for increasing the recording density of the magneto-optical recording medium.

  The linear recording density of the magneto-optical recording medium greatly depends on the laser wavelength λ of the reproducing optical system and the numerical aperture NA of the objective lens, and the spatial frequency at the time of signal reproduction is a limit where NA / λ can be detected. Therefore, in order to realize a high density with a conventional optical disc, it is necessary to shorten the laser wavelength of the reproducing optical system and increase the numerical aperture NA of the objective lens. However, there is a limit to improving the laser wavelength and the numerical aperture of the objective lens. For this reason, a technique called magnetic super-resolution for improving the recording density by devising the configuration of the recording medium and the reading method and various reproducing methods such as a magnetic domain expansion reproducing method have been proposed.

  However, the above reproduction method has a drawback that the reproduction signal amplitude is small.

  The applicant proposed in JP-A-6-29496 a magneto-optical recording medium, a reproducing method thereof, and a reproducing apparatus for reproducing a signal having a period equal to or less than the diffraction limit of light without reducing the reproducing signal amplitude at high speed. did.

  In this proposal, when a temperature distribution is formed in the reproducing magnetic layer of the magneto-optical recording medium by a heating means such as a light beam, the domain wall can be moved to the lower domain wall energy. As a result, the reproduction signal amplitude is always a constant and maximum amplitude irrespective of the recorded domain wall interval (ie, recording bit length), and the domain wall motion detection method (DWDD (Domain Wall Displacement Detection)). is called.

In principle, this playback system has no limit on the resolution in playback, and further, the inevitably lowering of the playback output accompanying the increase in recording density is greatly improved, and further higher density is realized. ing.
JP-A-6-29496

  However, in the conventional magneto-optical recording medium using the domain wall motion as described above, the domain wall motion phenomenon may not be reproduced with good stability.

  Accordingly, an object of the present invention is to provide a magneto-optical recording medium in which the domain wall motion is reproduced with good stability and the cross-write characteristics between adjacent tracks are good.

  The present invention relates to a magneto-optical recording medium that is formed on the surface of a substrate and that reproduces the magnetic domain by reproducing at least the domain wall of the magnetic layer to be reproduced. The surface roughness when the sloped surface of the land portion is divided into upper and lower parts is defined as upper Ra1 and lower Ra2, respectively. Ra1 <Ra2 This is a characteristic magneto-optical recording medium.

  The magneto-optical recording medium of the present invention can reproduce a magneto-optical recording medium by a domain wall motion type magnetic domain expansion reproducing system using a temperature gradient with good stability and at the same time improve the reproduction signal quality (jitter). Can be made.

The inventor can improve the surface property by performing O ₂ plasma ashing on the glass master for producing the stamper, but the groove shape becomes gentle, and the cross light characteristic between adjacent tracks deteriorates. In order to achieve the purpose of providing an ultra-high density magneto-optical recording medium using domain wall motion, the domain wall motion is reproduced with good stability. We found that the surface properties (surface roughness) of the magnetic layer involved in recording medium reproduction are related to the ease of domain wall movement, and found a substrate shape with good signal characteristics (jitter) and cross-write characteristics. It was.

  In order to achieve the above object, the present invention provides a magneto-optical recording medium which is formed on the surface of a substrate and expands the magnetic domain by moving at least the domain wall of the magnetic layer to be reproduced. The surface roughness when the inclined surface of the land portion is divided into upper and lower parts is expressed as upper Ra1 and lower Ra2, respectively. Then, the magneto-optical recording medium is characterized in that Ra1 <Ra2. In this case, the inclined surface of the land portion can be divided up and down on the land side with respect to the full width at half maximum of the land.

  In the magneto-optical recording medium of the present invention, at least a first magnetic layer, a second magnetic layer, and a third magnetic layer are sequentially laminated, and the first magnetic layer is formed on the third magnetic layer at a temperature near ambient temperature. The magnetic layer has a relatively small domain wall coercive force and a large domain wall mobility, and the second magnetic layer is a magnetic layer having a low Curie temperature of the first magnetic layer and the third magnetic layer. This is a magneto-optical recording medium.

  Further, according to the present invention, the reproducing magnetic layer is magnetically separated from each other between the information tracks, the surface roughness Ra of the upper portion of the land portion of the magnetic layer and the groove surface is 1.2 nm or less, and the inclined surface of the land portion is The magneto-optical recording medium is characterized in that the angle is 50 to 90 degrees.

  In the magneto-optical recording medium of the present invention, O2 plasma ashing is performed after performing RIE on the glass master so that the upper and lower Ra1 and Ra2 have Ra1 <Ra2 in the stamper forming process. It is a feature.

  The surface roughness Ra is a center line average roughness, and can be measured using a scanning probe microscope or the like.

  The present invention will be described in more detail with reference to the drawings.

  The structure of the magnetic layer of the magneto-optical recording medium of this embodiment will be described with reference to FIG. As shown in FIG. 4, a first dielectric layer 12, a magnetic layer (recording layer) 13, and a second dielectric layer 14 are laminated on the transparent substrate 11 in this order.

  As the transparent substrate 11, for example, glass, polycarbonate, polymethyl methacrylate, thermoplastic norbornene resin, or the like can be used.

  The recording layer 13 is a magneto-optical information recording layer of a type that reproduces the magnetic domain by moving the domain wall during reproduction. For example, the first magnetic layer disclosed in Japanese Patent Laid-Open No. Hei 6-290496 is used. The three-layer structure includes a layer 131, a second magnetic layer 132, and a third magnetic layer 133. Here, the first magnetic layer 131 is a magnetic layer (moving layer and reproducing layer) having a relatively small domain wall coercive force and a large domain wall mobility near the ambient temperature as compared with the third magnetic layer 133. The second magnetic layer 132 is a magnetic layer (switching layer) having a lower Curie temperature than the first magnetic layer 131 and the third magnetic layer 133, and the third magnetic layer 133 has excellent storage stability of the magnetic domains. It is a normal magnetic recording layer (memory layer). In this case, the magnetic layers are exchange-coupled or magnetostatically coupled to each other by continuously forming a film by a physical vapor deposition method such as sputtering or vacuum vapor deposition.

  As the first magnetic layer 131, a material for a bubble memory such as a rare earth-iron group amorphous alloy having a relatively small magnetic anisotropy, such as GdCo, GdFe, GdFeCo, or TbCo, or garnet is preferable. .

  As the second magnetic layer 132, for example, a Co-based or Fe-based alloy magnetic layer having a Curie temperature lower than that of the first magnetic layer 131 and the third magnetic layer 133 is preferable. Further, the Curie temperature can be adjusted by adding amounts of Co, Cr, Ti and the like.

  Examples of the third magnetic layer 133 include saturation magnetization and magnetic properties such as rare earth-iron amorphous alloys such as TbFeCo, DyFeCo, and TbDyFeCo, and platinum group-iron group periodic structure films such as Pt / Co / and Pd / Co. Those having a large anisotropy value and capable of stably maintaining the magnetization state (magnetic domain) are preferable.

  The first and second dielectric layers 12 and 14 are not particularly limited. For example, SIN, SiO2, ZnS, and the like are preferable.

  Moreover, you may form heat dissipation layers, such as Al alloy, as needed.

  The surface roughness of the first magnetic layer 131 involved in reproduction almost directly reflects the surface roughness of the substrate 11. Therefore, as a method for controlling the surface roughness of the magnetic layer, it is direct and simple to control the surface roughness of the surface of the substrate 11 on which the magnetic layer is formed.

  In the magneto-optical recording medium of the present embodiment, land portions and groove portions are formed on the substrate surface. The substrate shown in FIG. 2 includes a groove portion having a width 2a and a trapezoidal land portion having an upper width 1a from the substrate surface, an angle θ with respect to the substrate, and a height h4.

  The above-described substrate is manufactured by manufacturing a stamper using a plating method by using a glass master made by processing a quartz glass substrate as a master, and using the stamper. This will be described below with reference to the drawings.

  3 (1) to (5) are manufacturing process cross-sectional views showing the manufacturing process of the glass master (master) 30, and FIGS. 3 (6) to (9) show the manufacturing process of the stamper 31 using the glass master 20. It is manufacturing process sectional drawing shown.

Glass master 20
(1) A primer such as a silane coupling agent is applied on the surface of a quartz glass substrate 20 that has been precisely polished to a surface roughness Ra of 1 nm or less, and then a photoresist 21 is applied (FIG. 3 (1)). .
(2) Exposure to the desired specifications with the light beam 22 (FIG. 3 (2)),
(3) Development is performed using a developer such as an inorganic alkali to form a desired resist pattern 24 on the surface of the master (FIG. 3 (3)). If it is a positive resist, an unexposed part remains at the time of development, and the exposed part 23 (see FIG. 3B) is dissolved in the developer.
(4) After development, RIE (Reactive Ion Etching) 15 was performed to create a desired concavo-convex shape including the concave portion 28 and the convex portion 19 (FIGS. 3 (4) and (5)).
In the present embodiment, etching conditions are used in which the inclination angle of the convex portion is 60 °.
(5) Plasma ashing is performed to remove residual resist, and a glass master (master) 30 is formed (FIG. 3 (5)).

  As will be described later, the plasma ashing condition can be selected as appropriate so that the surface roughness of the convex portion 19 becomes a desired surface roughness.

Next, manufacture of a stamper using the glass master 30 will be described with reference to FIGS.
(6) After the Ni conductive film 36 is formed on the glass master 30 by sputtering 26 (FIG. 3 (6)),
(7) The Ni electroformed layer 37 is formed (FIG. 3 (8)),
(8) Peel (FIG. 3 (9)), then
(9) Plasma ashing is further performed on the peeled Ni electroformed layer 37 to remove the residual resist adhering to the pattern surface, thereby completing the stamper 21 (FIG. 3 (10)).

  Therefore, the surface roughness of the glass surface is reflected in the surface roughness of the stamper 31, and the surface roughness of the stamper is reflected in the surface roughness of the substrate used for the magneto-optical recording medium.

  When a substrate is manufactured using the stamper 31, the convex portion of the stamper 31 becomes a groove portion of the substrate and the concave portion becomes a land portion. If it is desired to use the convex portion of the stamper 31 as a land surface of the substrate, an inverse stamper may be created using the created stamper as a mother.

  By performing ashing (6) after the RIE steps (4) and (5), the surface roughness of the inclined portion of the land is improved.

  The surface roughness of the land inclined portion of the substrate 11 is reduced in both the upper and lower portions of the inclined portion of the convex portion by performing plasma ashing when the glass master 20 is manufactured. By controlling the plasma ashing, the surface roughness of the land inclined portion can be changed between the surface roughness (Ra1) of the upper part 3a and the surface roughness (Ra2) of the lower part 3b as shown in FIG. , Ra1 <Ra2.

  Ra1 <Ra2 when the surface roughness when the inclined surface of the land part is divided into upper and lower parts by the full width at half maximum of the land (shown by dotted lines in FIG. 1) is the upper Ra1 and the lower Ra2. More preferably.

  The surface roughness of the first magnetic layer 131 involved in reproduction and the surface roughness of other surfaces are indicated by Ra (average center line roughness) measured by a scanning probe microscope.

  Here, the surface roughness was measured by using an AFM (Atom Force Microscope), using a normal blade tip as the probe, and scanning the inclined portion in the track direction.

  The surface properties of the stamper, the injection-molded substrate, and the recording medium that are created from the master disc are almost the same as the Ra of the master disc.

  By using a magneto-optical recording medium having such a surface roughness, it has become possible to reproduce the domain wall movement phenomenon with good stability by the reproduction system using the domain wall movement detection system. This is because if the surface roughness (surface irregularities) of the shoulder portion of the land portion of the magneto-optical recording medium (the portion on the land side from the portion indicated by the dotted line in FIG. 1 and the upper side of the land inclined portion) is small, the domain wall moves. Suggests that this is done smoothly. On the other hand, in the groove portion, the smoothness on the lower side of the land inclined portion is somewhat inferior, but since the land angle θ is kept large, the magnetic film at the end of the groove portion after film formation is shown in FIG. It is considered that the domain wall is stably moved because a discontinuous portion is generated and this causes a magnetic division between the adjacent land portions of the groove portion. Further, the discontinuous portion of the magnetic film has not only a magnetic division but also a thermal division effect, so that it is possible to improve the cross write characteristics from adjacent tracks.

EXAMPLES The present invention will be described more specifically with reference to examples below, but the present invention is not limited to these examples. In these examples, the surface roughness Ra is measured using a scanning probe microscope (SPM: (Scanning Probe Microscope)) NanoScope III (manufactured by Digital Instruments Inc.) in a tapping mode AFM (Atom Force Microscope: atomic force microscope). Used, a normal blade tip was used as the probe, and the surface roughness at the above-mentioned position of the inclined portion was measured.
Example 1
The magneto-optical recording medium shown in FIG. 4 was manufactured.

Exposure (laser wavelength: 351 nm) and development were performed on the master coated with the resist, and RIE (CHF ₃ , RF 200 W, 30 sccm, 3.0 Pa, 9 min) was performed using the remaining resist as a mask. O ₂ ashing (RF 150 W, 80 sccm, 8.0 Pa, 30 min) was performed on the master from which the remaining resist was removed. The obtained master is a land / groove recording substrate with a track pitch of 0.32 μm. The height 4 of the land portion is 100 nm, and the angle θ of the land portion is 60 degrees. Since the time for O ₂ plasma ashing can be shorter than when the entire surface is smoothed, the angle θ of the land portion hardly changes in O ₂ plasma ashing. The surface roughness of the land upper part and the groove surface was 0.43 nm. The surface roughness of the land inclined portion was Ra1 = 0.56 nm and Ra2 = 1.52 nm in both the substrate 11 and the magneto-optical recording medium. A stamper was made by performing Ni sputtering and electroforming on this master, and a substrate was made by injection molding. The substrate 11 was made of polycarbonate.

  An SiN layer 12 as an interference layer is formed on the substrate 11 to a thickness of 80 nm, and then a GdFeCo layer 131 is formed as a first magnetic layer (domain wall moving layer) to a thickness of 30 nm, and a second magnetic layer (switching layer) is formed as DyFeFe. The layer 132 was formed to a thickness of 10 nm, and the TbFeCo layer 133 was formed to a thickness of 40 nm as a third magnetic layer (memory layer) by sequential sputtering. Finally, a SiN layer having a thickness of 80 nm was formed as a protective layer.

  The land shape of the magneto-optical recording medium thus obtained is shown in FIG. When the surface roughness of the inclined portion (actually, the upper surface of the second dielectric layer 14 as a protective layer) was measured, it was almost equal to the surface roughness of the land inclined portion of the substrate 11. Therefore, it can be said that the surface roughness of the domain wall motion layer (reproduction layer) 131 is substantially the same.

A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. No. 6-290496), a jitter value of 8% was stably obtained with good reproducibility for both land and groove in an optical system having a wavelength of 405 nm and NA of 0.65 (relative speed of 2 m / s). Further, the cross-write characteristics from adjacent tracks were also good, and a power margin of ± 20% of the recording power center value of land and groove was obtained. However, the power margin was defined in a range where the jitter value was 15% or less.
(Comparative Example 1)
The magneto-optical recording medium shown in FIG. 4 was manufactured. Plasma ashing conditions after RIE were performed under (RF150W, 80 sccm, 8.0 Pa, 3 min), and the surface roughness of the land inclined portion on the master was Ra1 = 1.52 nm and Ra2 = 1.52 nm. Moreover, the surface roughness of the land upper part and the groove surface was both 0.43 nm. The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

  A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. 6), the jitter value was 16% at the land portion and 14% at the groove portion in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed 2 m / s).

The reason why the jitter value of the land portion deteriorated is that the smoothness of the land shoulder portion is inferior to the embodiment of the present invention, which seems to be an obstacle to the domain wall movement in the land portion.
(Comparative Example 2)
The magneto-optical recording medium shown in FIG. 4 was manufactured. Plasma ashing conditions after RIE were performed (RF 150 W, 80 sccm, 8.0 Pa, 75 min), and the surface roughness of the land inclined portion in the master was Ra1 = Ra2 = 0.56 nm. (The surface roughness of the land upper part and the groove surface were both 0.43 nm.) The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. No. 6-290496), a jitter value of 12% / 14% for both land / groove was stably obtained with good reproducibility in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed of 2 m / s). It was. However, the cross write characteristics from adjacent tracks deteriorated, and only a power margin of ± 10% of the recording power center value of the land and groove was obtained. The reason why the power margin deteriorated is considered to be that although the smoothness of the side wall portion was improved by plasma ashing, the land angle θ became gently 40 °, and the heat at the time of adjacent track recording was easily transferred.
(Example 2)
The magneto-optical recording medium shown in FIG. 4 was manufactured. The plasma ashing conditions after RIE were performed under the conditions of (RF 100 W, 30 sccm, 3.0 Pa, 3 min), and the surface roughness of the land inclined portion in the master was Ra1 = 0.56 nm and Ra2 = 1.52 nm. The surface roughness of both the land surface and the groove surface was 1.2 nm. The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. 6), the jitter value was 12% at the land portion and 12% at the groove portion in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed of 2 m / s).
(Comparative Example 3)
The magneto-optical recording medium shown in FIG. 4 was manufactured. The plasma ashing conditions after RIE were performed under the conditions of (RF 100 W, 30 sccm, 3.0 Pa, 2 min), and the surface roughness of the land inclined portion in the master was Ra1 = 0.56 nm and Ra2 = 1.52 nm. The surface roughness of the land upper part and the groove surface was 1.8 nm. The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. 6), the jitter value was 20% at the land portion and 18% at the groove portion in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed of 2 m / s).
(Example 3)
The magneto-optical recording medium shown in FIG. 4 was manufactured. Plasma ashing conditions after RIE were performed under the conditions of (RF 300 W, 80 sccm, 8.0 Pa, 30 min), and the surface roughness of the land inclined portion on the master was Ra1 = 0.56 nm and Ra2 = 1.52 nm. The surface roughness of the land upper part and the groove surface was both 0.43 nm. The angle of the inclined part was 30 °. The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. 6), the jitter value was 11% at the land portion and 12% at the groove portion in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed 2 m / s).
(Comparative Example 4)
The magneto-optical recording medium shown in FIG. 4 was manufactured. Plasma ashing conditions after RIE were performed (RF 300 W, 80 sccm, 8.0 Pa, 40 min), and the surface roughness of the land slope portion on the master was Ra1 = 0.56 nm and Ra2 = 1.52 nm. The surface roughness of both the land upper part and the groove surface was 0.43 nm. The angle of the inclined part was 20 to 25 °. The land shape of the obtained magneto-optical recording medium is shown in FIG. All other conditions were the same as in Example 1.

  A continuous magnetic domain having a pit length of 0.15 μm is recorded in the track direction by the magnetic field modulation method on the magneto-optical disk thus obtained. 6), the jitter value was 21% at the land portion and 20% at the groove portion in an optical system having a wavelength of 405 nm and an NA of 0.65 (relative speed of 2 m / s).

It is typical sectional drawing seen from the upper direction of the board | substrate used for the magneto-optical recording medium of this invention. It is a typical sectional view of a substrate used for a magneto-optical recording medium of the present invention. It is machine cross-sectional drawing which shows the example of 1 process of the manufacturing method of the conventional board | substrate. It is sectional drawing which shows an example of the film | membrane structure of a magneto-optical recording medium. It is a SPM image (Example 1) of the board | substrate used for the magneto-optical recording medium of this invention. It is a SPM image (comparative example 1) of the board | substrate used for a magneto-optical recording medium. It is a SPM image (comparative example 2) of the board | substrate used for a magneto-optical recording medium. It is a SEM image for demonstrating the mode of the magnetic film of the magneto-optical recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Land part 1a Land upper part 2 Groove part 2b Groove surface 3 Inclined part of land part 3a Upper part of inclined part of land part 3b Lower part of inclined part of land part 4 Height of land part θ Angle of land part 11 Transparent substrate 12 First 1 dielectric layer 13 magnetic layer 14 second dielectric layer 131 first magnetic layer 132 second magnetic layer 133 third magnetic layer 20 quartz glass substrate 21 photoresist 22 light beam 23 exposed portion 24 resist pattern 25 RIE (Reactive Ion Etching)
26 Sputter deposition 28 Concave part 29 Convex part 30 Glass master (master)
31 Stamper 36 Ni conductive film 37 Ni electroformed layer

Claims (8)

In a magneto-optical recording medium that reproduces by expanding the magnetic domain by moving at least the domain wall of the magnetic layer formed on the substrate,
A land portion and a groove portion are formed on the surface of the substrate,
2. A magneto-optical recording medium according to claim 1, wherein when the inclined surface of the land portion is divided into upper and lower portions, the upper surface roughness Ra1 and the lower surface roughness Ra2 have a relationship of Ra1 <Ra2.   2. The magneto-optical recording medium according to claim 1, wherein the inclined surface of the land portion is divided vertically on the land side with respect to the full width at half maximum of the land.   The magnetic layer is a magneto-optical recording medium in which at least a first magnetic layer, a second magnetic layer, and a third magnetic layer are sequentially stacked, and the first magnetic layer is formed at a temperature near ambient temperature. A magnetic layer having a relatively small domain wall coercive force and a large domain wall mobility compared to the third magnetic layer, and the second magnetic layer is a magnetic layer having a low Curie temperature of the first magnetic layer and the third magnetic layer. 3. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is a layer.   4. The magneto-optical recording medium according to claim 1, wherein the reproducing magnetic layer is magnetically separated from each other between the information tracks. OK.
5. The magneto-optical recording medium according to claim 1, wherein the surface roughness Ra of the upper portion of the land portion of the reproducing magnetic layer and the groove surface is 1.2 nm or less.   6. The magneto-optical recording medium according to claim 1, wherein an angle of the inclined surface of the land portion is 30 to 90 degrees.   The surface roughness when the inclined surface of the land portion is divided into upper and lower parts on the land side with respect to the full width at half maximum of the land is defined as Ra1 <Ra2 when the upper surface Ra1 and the lower surface Ra2 are provided. 1. The magneto-optical recording medium according to 1. A method for producing a glass master, wherein a substrate for a magneto-optical recording medium having a land part and a groove part is produced using a stamper formed from the glass master,
Forming a mask pattern on the glass substrate;
Etching and removing the substrate using the mask pattern as a mask, and forming irregularities corresponding to the land and groove portions of the substrate on the glass substrate surface;
When the surface roughness of the surface corresponding to the upper portion of the inclined surface of the land portion of the substrate of the concavo-convex portion of the glass substrate is Ra1, and the surface roughness of the surface corresponding to the lower portion is Ra2, Ra1 < And a step of removing the mask pattern using plasma ashing so as to be in the relation of Ra2.

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