JP2001126333A - Substrate for information recording medium, method for manufacturing master disk and device for exposing master disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate and an information recording medium provided with prepits having a shape suitable for the recording of high density. SOLUTION: The device 100 for exposing a master disk is provided with a magneto-optical head 27 having a magnetic head and impresses a magnetic field of the polarity in accordance with pits forming signal on a photoresist 20 applied on the master disk 19. The photoresist 20 is dispersed with magnetic fine particles which can be assembled by a magnetic field and form a magnetic mark. The exposure to the photoresist formed with the magnetic mark affords a pattern in which the region other than the magnetic mark is exposed. The magnetic mark of a rectangle having the linear directional length of the order of 80 nm can be formed and the pits having a similar shape are formed on the master disk and the substrate obtained from the master disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate for a high-density information recording medium on which prepits in which the shortest prepits are shorter in the track direction than in the track width direction, and a master for manufacturing such a substrate. Master exposure method,
The present invention relates to a master exposure apparatus and a photosensitive material used for the same.

[0002]

2. Description of the Related Art In an optical recording medium such as a CD-ROM and a DVD-ROM, information is reproduced by optically detecting a pit pattern formed on a substrate according to recorded information. These pit patterns are usually formed through master exposure, development, duplication of a stamper, and injection molding using a stamper. In the master exposure process, after a photoresist is applied on a glass master, a laser beam is irradiated in a pattern corresponding to recorded information, and the photoresist is exposed (exposed) in the pattern. Here, the intensity distribution of the laser light used follows a Gaussian distribution,
The exposed pattern has a circular or elliptical shape extending in the track direction. Therefore, such a circular or oval pit is formed on the master obtained through the developing process, the stamper for injection molding, and the substrate injection-molded using the stamper.

[0003]

As described above, the shape of the pits formed on the substrate of the conventional optical recording medium is limited by the laser beam irradiated at the time of exposing the master, and the length of the pit is the longest in the track direction. The short pit, ie, the smallest pit, was circular. However, such conventional pit shapes are not necessarily suitable for high-density recording and reproduction.

A first object of the present invention is to provide an information recording medium substrate having a novel pit shape and a high-density information recording medium using the same.

A second object of the present invention is to provide a new master, a master exposure method and a master exposure apparatus capable of exposing a pit shape suitable for high-density recording.

A third object of the present invention is to provide a novel photosensitive material suitable for the master exposure method provided by the present invention.

According to a first aspect of the present invention, there is provided a method of manufacturing a master having an uneven pattern used for manufacturing a substrate for an information recording medium, the method comprising: Is applied on a flat surface of the master, and a magnetic field is applied to the master according to recorded information to form a magnetic mark composed of an aggregate of magnetic fine particles in the photosensitive material, and the photosensitive material is exposed by exposing the photosensitive mark. A method for manufacturing a master disc, comprising exposing a photosensitive material according to a mark pattern of a magnetic mark and developing the exposed photosensitive material.

In the method of manufacturing a master according to the present invention, a photosensitive material in which magnetic fine particles are dispersed is prepared in advance, and is applied to a master such as a glass plate. The components and concentrations of the photosensitive material and the magnetic fine particles are selected so that the magnetic fine particles can migrate or move in the photosensitive material according to an applied magnetic field, as described later in detail. A magnetic field having a polarity corresponding to the recorded information is applied to the master on which the photosensitive material has been applied in this manner, and a magnetic mark composed of an aggregate of magnetic fine particles is generated in the photosensitive material. The magnetic mark is
For example, by using a magnetic head as used in a hard disk, the length of the master in the track direction (linear direction) is shorter than the length in the track width direction.
A rectangular magnetic mark can be formed. The length of the rectangular magnetic mark in the track direction is λ / (2NA) (where,
λ is the wavelength of the exposure light of the master exposure apparatus, and NA is the numerical aperture of the objective lens used in the master exposure apparatus), for example, about tens of nm. Next, when the photosensitive material is exposed, the portion where the magnetic mark exists is not exposed because the light is absorbed by the magnetic mark and the inside of the photosensitive material is shielded, and only the portion where the magnetic mark does not exist is exposed. It is exposed. That is, a photosensitive pattern of the photosensitive material is formed according to the pattern of the magnetic mark.
Therefore, according to the method of the present invention, the polarity of the magnetic field is reversed according to the recording information, instead of forming a photosensitive pattern by turning light on and off according to the recording information for forming a pit, as in the related art. By doing so, a photosensitive pattern is formed. It is desirable that a DC magnetic field be applied to the photosensitive material in the direction of travel of the disk in addition to the magnetic field that is inverted in accordance with the recorded information, so that the edges of the recorded marks are further emphasized.

Next, by developing the master disc exposed as described above, a concavo-convex pattern reflecting the pattern of the magnetic mark is formed. If it is desired to make the magnetic mark portion a convex pattern, it is sufficient to select a photosensitive material (positive photoresist) in which the exposed portion is etched by development, and the magnetic mark portion is formed into a concave pattern. If it is desired to do so, a photosensitive material (negative photoresist) may be selected such that the unexposed portion (the portion where the magnetic mark is formed) is etched by development.

According to a second aspect of the present invention, in a method of manufacturing a master having an uneven pattern used for manufacturing an information recording medium substrate formed on a surface, magnetic fine particles are dispersed in a liquid. The magnetic fine particle liquid is applied on the flat surface of the master, and a magnetic field is applied to the magnetic fine particle liquid on the master according to the recorded information to generate a magnetic mark composed of an aggregate of magnetic fine particles in the magnetic fine particle liquid. A method for manufacturing a master is provided, wherein a convex portion made of a magnetic mark is formed on the master by removing the liquid from above, and the convex portion is fixed on the master.

[0011] In the manufacturing method according to the second aspect of the present invention,
A magnetic fine particle liquid in which magnetic fine particles are dispersed in a liquid such as an organic solvent or oil is applied on a master, and a magnetic field is applied to a desired position on the master to cause the magnetic fine particles to migrate in the liquid to obtain a desired magnetic material on the master. Gather at a location. Next, after forming such an aggregate of magnetic fine particles in a desired pattern on the master, the liquid is removed from the master by, for example, drying. Since the aggregate of the magnetic fine particles has a thickness, a convex portion is formed on the master. In order to fix the convex portion formed of the aggregate of the magnetic fine particles on the master, a protective film such as silicon nitride may be coated on the master on which the irregularities are formed. In this manner, a master on which an uneven pattern is formed is obtained.

A rectangular pit similar to the magnetic mark can be formed on a substrate manufactured from a stamper obtained by duplicating a master obtained by the method according to the first or second aspect of the present invention. . As described above, according to the master manufacturing method of the present invention, the length different from the conventional circular or long hole, particularly, the length in the track direction (length in the vertical direction) is changed to the length in the track width direction (length in the horizontal direction) It is possible to form shorter rectangular pits (having an aspect ratio of less than 1).

The reason why such a rectangular pit is effective will be described with reference to FIGS. As shown in FIG. 1, the conventional circular pit 63 has a diameter which is about half the track width of the track 61, and a rectangular pit 65 having the same area as the pit 63 has a track direction as shown in FIG. Is shorter than the circular pit 63. Therefore, when the rectangular pits 65 are used, the pits can be densely packed in the track direction as compared with the circular pits, whereby the storage capacity can be increased. Even when a circular pit is used and when the recording density is the same, the interval between a pair of adjacent pits is shorter in a rectangular pit than in a circular pit. It is further suppressed.

As shown in FIG. 2, the circular pits 63 and the rectangular pits 67 having the same length in the track direction have the same length in the track direction and the same recording density. The area is larger than the circular pit. Therefore, as will be described later in the embodiment, the reproduction signal intensity generated from the recording layer portion in the rectangular pit is larger than that in the case of the circular pit.

According to a third aspect of the present invention, there is provided a method for manufacturing a substrate for an information recording medium, comprising a plurality of convex portions formed from an aggregate of magnetic fine particles on a flat master disk. A master is provided. This master is obtained by the manufacturing method according to the second aspect of the present invention.

According to a fourth aspect of the present invention, there is provided a master exposure apparatus used for manufacturing a substrate for an information recording medium and exposing a master coated with a photosensitive material in a predetermined pattern. A magnetic head for applying a magnetic field to the master according to the pattern, and a light source for exposing the photosensitive material, wherein the photosensitive material comprises:
A photosensitive material in which magnetic fine particles movable by a magnetic field applied from the magnetic head are dispersed, and an external magnetic field is applied by the magnetic head to form a magnetic mark composed of an aggregate of magnetic fine particles in the photosensitive material. A master exposure apparatus is provided, wherein the photosensitive material on which the magnetic mark is formed is exposed by a light source.

The master exposure method of the present invention can be carried out using the master exposure apparatus according to the present invention. The magnetic head provided in the master exposure apparatus of the present invention applies a magnetic field having a different polarity to a photosensitive material in which magnetic fine particles are dispersed according to a pit formation signal. The magnetic head is not particularly limited, but is preferably a magnetic head having a narrow gap width. For example, a magnetic head used in a hard disk device such as a ferrite monolithic type, a thin film type, and a metal-in-gap type is preferable. Since these magnetic heads can form a magnetic mark having a length of about 80 nm in the track direction of the disk, the recording density (linear recording density) in the track direction can be increased. Further, a magneto-optical head having a magnetic coil wound near the solid immersion lens may be used. The light source used in the master exposure apparatus of the present invention may be a light source that emits light having a wavelength for sensitizing the photosensitive material, and a light source used in a normal master exposure apparatus may be used. However, as mentioned above,
In the present invention, since the photosensitive pattern is not formed by turning on / off the laser light, the light source may be continuous light or intermittent light.

The master exposure apparatus according to the present invention further includes a moving device for moving the master with respect to the magnetic head and the light source, and the magnetic head is positioned forward of the light source with respect to the moving direction of the master by the moving device. Can be deployed. By arranging the magnetic head and the light source in this way, after the magnetic mark is formed on the photosensitive material by the magnetic head, the photosensitive material before and after the magnetic mark is exposed to light from the light source.

Further, the master exposure apparatus may include a slider on which the magnetic head is mounted and moves on the master. To apply the magnetic field from the magnetic head to the narrowest possible area of the photosensitive material without weakening, it is necessary to bring the magnetic head close to the photosensitive material, for which the magnetic head is mounted on a slider, Preferably, the slider is moved over the photosensitive material. Furthermore, an arm is provided for supporting the slider so that it can float above the master, and the arm can be supported on a support plate together with an optical element (optical head) for forming an exposure spot. Further, a magnetic head control device may be provided for applying a magnetic field having a polarity corresponding to the recorded information to the magnetic head.

According to a fifth aspect of the present invention, there is provided a photosensitive material comprising magnetic fine particles dispersed therein, wherein the magnetic fine particles can move within the photosensitive material by applying a magnetic field. Materials are provided. It is also effective to increase the solvent amount of the photosensitive material in order to increase the moving speed.

The photosensitive material according to the present invention is suitably used for the master exposure apparatus and the master exposure method of the present invention. The photosensitive material includes magnetic fine particles dispersed therein, and the magnetic fine particles can move or migrate within the photosensitive material according to an applied external magnetic field. For this reason, the magnetic fine particles move to a portion to which the external magnetic field is applied and gather there to form a magnetic mark. Since the magnetic mark concentrates particularly on the surface of the photosensitive material, light enough to expose the photosensitive material below the magnetic mark does not reach the magnetic mark. Therefore, only the portion of the magnetic mark is not exposed, and only that portion remains on the master as a convex portion (or concave portion) through the developing process. That is, the photosensitive pattern of the photosensitive material of the present invention is determined not by the on / off or intensity distribution of light irradiated for exposure, but by the reversal of the polarity of the external magnetic field and the shape of the magnetic mark formed thereby. become. Therefore, it is possible to form not only a conventional circular pattern but also a rectangular, crescent, arrow feather, and bar code type photosensitive pattern. The length of the prepit in the information reading direction (track direction) is λ / (3N
A) (where λ is the wavelength of the reproduction light when reproducing the information recording medium, and NA is the numerical aperture of the lens for condensing the reproduction light on the information recording medium). Can be.

As the photosensitive material in which the magnetic fine particles are dispersed, for example, a photoresist such as cresol or novolak resin generally used for master disk exposure can be used. The photoresist may be either a positive type or a negative type. On the other hand, the magnetic fine particles are, for example, γ-Fe ₂ O ₃ , C
rO ₂ , barium ferrite (BaFe ₁₂ O ₁₉ ),
Co, Fe, Ni, Co-Fe, Pt-Co, Ni-F
e, Co-Ni, Pd-Co, garnet are used,
The particle size is 30 nm because the recording mark ends are aligned.
The following is preferred. The viscosity of the photoresist and the concentration of the magnetic fine particles are such that the magnetic fine particles can move in the photoresist in accordance with the applied magnetic field, and the photosensitive material is substantially reduced in the portion of the photosensitive material to which the magnetic field is applied. It can be appropriately determined according to the photosensitive material, the magnetic fine particles, and the strength of the external magnetic field to be used so that the covering magnetic mark is formed. For example, the concentration of the magnetic fine particles in the photoresist can be adjusted to 10 to 50%. Specifically, in the photosensitive material, magnetic fine particles C
o It is preferable to disperse ferrite fine particles. This photosensitive material can be applied on the master by spin coating or dipping. The thickness of the photosensitive material is not particularly limited, but is preferably submicron or less for the reason of shortening the shortest mark.

According to a fourth aspect of the present invention, in the information recording medium substrate having prepits formed in the information reading direction, the length of the prepits in the information reading direction is shorter than the length in the direction orthogonal to the prepits. Is provided, and a substrate is provided.

In the substrate of the present invention, the pre-pits for pre-formatting such as pre-pits or address pits for information recording, clock pits or servo pits are arranged in the information reading direction, for example, in the case of a disc-shaped information recording medium, Since it is formed at a high density in the direction (linear direction), it is suitable as a substrate for a high-density recording medium. In particular, in the case of a conventional substrate such as an optical disk, the minimum pit is circular, but in the case of the substrate of the present invention, as described with reference to FIG. The pit density per hit can be improved. The pit shape can be rectangular, crescent, or arrow feathers corresponding to the shape of the magnetic mark described above, and the length of the pit in the information reading direction (track direction) is 0.1 mm.
It can be 3 μm or less.

The substrate of the present invention can be a substrate having a roughened surface by being formed by the master exposure method of the present invention. Since the magnetic mark composed of the magnetic fine particles formed by the above-described master exposure method remains on the surface of the developed photosensitive material, the surface is roughened (fine irregularities).
Exists. This surface roughness is transferred to a stamper formed by duplicating a master and further to a substrate surface formed by injection molding or the like. As will be described later, when the information recording medium is a phase-change optical recording medium, this roughened portion can function as a site where crystal nuclei are generated. I can do it. Further, when a magneto-optical recording medium is formed by laminating a magnetic film on the roughened substrate, the coercive force of the magnetic material existing in the roughened portion is higher than that of the magnetic material existing in the flat portion. Since the coercive force is increased, a novel magneto-optical recording medium utilizing this difference in coercive force and a recording method thereof are provided.

According to a fifth aspect of the present invention, in an information recording medium having a substrate on which prepits are formed in the information reading direction, the length of the prepits in the information reading direction is greater than the length in the direction perpendicular to the prepits. An information recording medium characterized by forming short prepits is provided.

Since the prepits of the information recording medium of the present invention are formed at a high density in the information reading direction, pit information is recorded at a high density. Further, at least an information recording layer may be provided on the substrate. That is, the information recording medium can be a magneto-optical recording medium, a phase-change optical recording medium, or a dye recording layer.

The information recording medium of the present invention is also characterized in that the surface of the concave or convex portion of the substrate defined by the prepits is rough. When the information recording medium is a magneto-optical recording medium, the magnetization in the erasing or initializing direction can be recorded in the magnetic layer portion located on the roughened portion of the substrate. When the information recording medium is a phase-change recording medium, light irradiation may crystallize a recording layer portion located on a portion of the substrate whose surface is roughened.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

Example 1 I. Preparation of Photosensitive Material and Master Disc First, a method for preparing a photosensitive material according to the present invention will be described.
A photoresist as a photosensitive material is diluted with alcohol. With respect to 70 parts by weight of the diluent, as magnetic fine particles,
Co ferrite particles having an average particle diameter of 20 nm are added so as to have a ratio of 30 parts by weight, and mixed so that the magnetic fine particles are uniformly dispersed.

The mixed solution is applied on a glass master using a spin coater so as to have a thickness of about 60 nm.

II. Master Exposing Apparatus A specific example of a master exposing apparatus according to the present invention will be described with reference to FIGS. The master exposure apparatus 100 shown in FIG.
Mainly, a laser light source 1 for emitting laser light for exposure, an acousto-optic (AO) modulator 7 and an acousto-optic (AO) deflector 9 for adjusting the irradiation timing and irradiation position on the master 19, respectively, and the magneto-optical head 27 , A turntable 21 for rotating the master 19, an image pickup tube 24 and a display 26 for observing magnetic marks and irradiated spots, and various optical element groups for adjusting the optical path of laser light.

The magneto-optical head 27 includes the moving holder 2
8 is supported at the lower end. The moving holder 28
A guide 28a provided on the moving holder 28 slidably engages a rail 29 extending in the radial direction of the master. Further, a pinion and a pinion drive motor (both not shown) are mounted on the moving holder 28, and a rack (not shown) that meshes with the pinion is provided on the rail 29. The moving holder 28 can slide on the rail 29 in the radial direction of the master by the rotational force of the pinion transmitted from the drive motor. The driving of the motor is controlled by the control device 110. That is, the position of the magneto-optical head 27 moved by the moving holder 28 in the radial direction of the master 19 is controlled by the control device 110. As will be described later, the operation of the master exposure apparatus 100 is collectively managed by the controller 110.

Next, the optical system of the master exposure apparatus will be described. A laser beam 2 emitted from a laser light source 1 is split into a first beam 4 and a second beam 5 by a beam splitter 3. The first light beam 4 is incident on an AO modulator 7 sandwiched between a pair of lenses 6, and can be modulated into pulse light according to the timing of a signal to be recorded. After the pulse light modulated by the AO modulator 7 is reflected by the mirror 8,
The light is incident on the AO deflector 9 and is deflected so as to irradiate a predetermined radial position of the master 19. Next, the deflected light is incident on the magneto-optical head 27 via the polarizing mirror 10 and the mirror 11. The magneto-optical head 27 has a relay lens 1
5 and an objective lens 17 are mounted, and the laser light is focused on a predetermined position on the surface of the master 19 by these lenses. A magnetic head is mounted on the magneto-optical head as described later. Note that the irradiation timing and the exposure amount may be modulated by the EO modulator 12 instead of the AO modulator 7. In this case, the second light beam 5 incident on the EO modulator 12 is used as a light beam for exposure. Light that has passed through the EO modulator 12 is reflected by the half mirror 13 and
After passing through the two-phase plate 14, the polarizing mirror 10, the mirror 1
The light reaches the optical head 27 via 1.

In the ordinary master exposure method, the laser beam for exposure is modulated in a pulse form by the AO modulator 7 or the EO modulator 12 in accordance with the exposure pattern (pit forming pattern). For example, since the exposure pattern is determined by the pattern of the magnetic mark formed by the magnetic head as described later, the laser beam for exposure does not necessarily need to be pulse-modulated.

On the master disk 19, the photoresist 20 prepared in the above I, in which the magnetic fine particles are dispersed, is applied. The light emitted from the magneto-optical head 27 to the photoresist 20 on the master 19 has an exposure spot diameter of about 0.5 μm, and exposes the photoresist 20 in the exposure spot.

The light reflected from the surface of the photoresist 20 on the master 19 is reflected by the objective lens 18 and the relay lens 15.
, And becomes parallel light, and the mirror 11 and the polarizing mirror 1
0, the imaging tube 2 by the lens 22 through the half mirror 13
4 are collected. By observing the spot images 26a and 26b displayed on the display 26 of the imaging tube 24, the spot shape and the magnetic mark formed by the objective lens 18 can be confirmed.

FIG. 4 is a top view of the magneto-optical head 27. The magneto-optical head 27 includes a support plate 27 in which an opening 33 and an opening 35 are formed, an objective lens 17 that covers the opening 33, a magnetic head 39 supported through an arm 37 in the opening 35 on the support plate. Is provided. For convenience of explanation, the relay lens 15 is omitted from FIG. As the magnetic head 39, a magnetic head similar to the magnetic head used in the hard disk device can be used. The magnetic head 39 is supported by a slider 41, and the slider 41 is supported by the support plate 31 via an arm 37.

The light incident on the objective lens 17 passes through the first opening 33 and reaches the photoresist 20 of the master 19,
This produces an exposure spot. Here, the opening 3 for the magnetic head
5 and an opening 33 for light transmission are arranged side by side in the direction of rotation of the master 19, that is, in the track direction, and an opening 35 for the magnetic head is provided in the direction of rotation of the master (rotation direction). The support plate 31 is positioned relative to the master such that the support plate 31 is located forward of the master 33. With this arrangement, when the master 19 is rotated, a magnetic field is first applied by the magnetic head 39 to a region of the photoresist 20 where a predetermined photosensitive pattern is to be formed, and the magnetic mark is formed by magnetic fine particles. Is formed, and the region of the photoresist 20 including the magnetic mark is exposed to the exposure laser beam transmitted through the objective lens 17. The magnetic head 39 is connected to the control device 110, and the polarity and timing of the magnetic field applied from the magnetic head 39 to the photoresist 20 are controlled by the control device 110.

The operation of the master exposure apparatus shown in FIGS. 3 and 4 and the exposure method using the master exposure apparatus will be described below. The control device 110 drives the motor provided on the moving holder 28 to move the moving holder 28 until the magneto-optical head 27 is located immediately above the innermost exposure start position of the master. Next, the turntable 21
As a result, the master 19 is rotated with respect to the magneto-optical head 27, and the laser beam from the laser light source 1 is focused on the photoresist on the master 19 from the lens 17 of the magneto-optical head 27. At this time, the laser light is irradiated as continuous light without being pulsed by the AO element 7. Control device 110
Controls the moving holder 28 to gradually move outward (to the left in FIG. 3) of the master in the radial direction as the turntable 21 rotates. By such an operation, the photoresist 19 is spirally exposed from the inside to the outside of the master.

During the continuous exposure with the laser light, the magnetic head 39 moves the area (hereinafter, referred to as a pit) where information (pits) is recorded.
Pit formation area)
A magnetic field having a predetermined polarity, for example, a downward magnetic field in the figure is applied to form a magnetic mark in the pit formation region. The magnetic mark is formed by the magnetic fine particles in the photoresist gathering in the pit formation region by the applied magnetic field. In particular, the magnetic fine particles gather on the photoresist surface in the pit formation region to form a magnetic mark. Here, the laser light from the laser light source 1 is continuously applied to the photoresist 20.
The laser beam cannot reach the inside of the photoresist 20 where the magnetic mark is formed on the surface, and the pit formation region is not exposed. Therefore, the photosensitive pattern is formed in a pattern opposite to the pattern of the magnetic mark.

Here, the relationship between the magnetic mark formed by the magnetic head 39 and the exposure laser spot for exposing the magnetic mark will be described with reference to FIG. FIG. 5 shows a state in which the n-th track of the master disk 19 is exposed by the exposure laser spot 82, and a state immediately after the magnetic head 80 has formed the magnetic mark 80 in the pit formation area on the n-th track. Is represented. Immediately after the formation of the magnetic mark 80, the central portion 80b of the magnetic mark 80 is scanned by the exposure spot 82 following the magnetic mark 80. Here, the magnetic mark 80 has a horizontally long shape with a length in the track direction and a length in the track width direction of about 80 nm and about 1 μm, respectively, while the track pitch and the exposure spot diameter are about 0.3 μm. Therefore, the left end 8 of the magnetic mark 80 is also placed on the adjacent (n + 1) th and (n−1) th tracks.
0a and 80c protrude, respectively. However, since the exposure spot diameter is equal to the track width, n
Only the th track is scanned.

Next, when the (n + 1) th track is exposed by the exposure spot 82, the left end portion 80a of the magnetic mark 80 recorded on the nth track remains, but the magnetic head forms the magnetic mark at that position. When not (when the left end portion 80b is not a pit formation area)
, An external magnetic field of opposite polarity is applied, that is, the magnetic mark 80a disappears due to overwrite recording. Next, the area is scanned and exposed by the exposure spot 82. As described above, in the master exposure apparatus of the present invention, information is recorded in the form of a magnetic mark for each track, and immediately after that, the area other than the magnetic mark (pit forming area) for scanning the track with continuous light is used. All are exposed.
In this way, a magnetic mark is formed according to information to be recorded on all tracks, and an area where no magnetic mark is formed can be continuously exposed.

III. Substrate Manufacturing Method By developing the master exposed as described above with a developing solution, only the photoresist portions on which magnetic marks have been formed remain on the master as convex patterns. Since this magnetic mark is an aggregate of magnetic fine particles, fine irregularities (roughness) are generated on its surface.

The mastering process is completed after the master is made conductive. Next, nickel is electroformed to prepare a mother, and a nickel stamper is obtained by electroforming. Thus, a stamper having the same pattern as that of the master can be formed. Surface roughness is transferred to the surface of the protrusion of the stamper via a mother. Here, depending on the use of the stamper, this surface roughness can be polished with a grinder or the like to make the surface flat. In order to manufacture a substrate for a CD-ROM to be described later, it is preferable to polish the surface of the protrusion of the stamper. The mother may be formed by electroforming nickel from the master, and the mother to nickel pattern may be formed by electroforming nickel. In this case, a substrate having the same pattern as the master is finally obtained.

Finally, the stamper is loaded into an injection molding machine, and a molten resin such as polycarbonate is injected into a mold to mold a substrate having a pattern opposite to that of the stamper, that is, a master and a pattern opposite to the master. Can be. As described above, the photosensitive pattern is determined by the magnetic mark, and the magnetic mark can form a rectangular mark having an aspect ratio of less than 1 by using a magnetic head.
The pits formed on the substrate also have such rectangular pits.

IV. Manufacture of CD-ROM A board for a CD-ROM is manufactured according to the method of manufacturing a board. The substrate has an outer diameter of 120 mm and a center hole of 15 mm.
mm, a polycarbonate substrate having a thickness of 1.2 mm.
A guide groove and a land partitioned between the guide grooves are formed on the substrate. The track pitch is 1.6 μm. A rectangular information recording pit is formed in the information recording area, and the pit (unit pit) having the shortest length in the track direction is provided.
Had a length in the track direction of 80 nm and a length in the track width direction of 1 μm.

On this substrate, Al was laminated as a reflective film by sputtering, and then an ultraviolet cured film as a protective film was applied by spin coating to produce a CD-ROM. In this CD-ROM, as shown in FIG. 1, the length of a unit pit in the track direction can be made shorter than that of a conventional circular pit. Therefore, a CD-ROM having a substrate on which such a circular pit is formed can be used. In comparison, it is possible to reduce the interference between the waveforms of the reproduced signals from the pit and the pits preceding and following the pit.

V. Manufacturing of a magneto-optical disk A substrate for a magneto-optical disk is manufactured in the same manner as in the manufacturing method of the substrate except that a stamper is manufactured from the master through nickel patterns of a father and a mother.
In the substrate thus obtained, the convex portions correspond to the convex portions of the master, that is, the regions where the magnetic marks are formed. For this reason,
In the master exposure step, a magnetic mark was formed in an area where information was not recorded (an area where pits were not formed), so that the exposed area was a pit formation area. On the surface of the convex portion of this substrate, surface roughness remains due to the magnetic marks as in the case of the master. The substrate is a polycarbonate substrate having an outer diameter of 90 mm, an inner diameter of 15 mm, and a thickness of 1.2 mm. A guide groove and a land partitioned between the guide grooves are formed on the substrate. The track pitch is 0.6 μm. A rectangular information recording pit is formed in the land portion of the information recording area. The pit (unit pit) having the shortest length in the track direction has a length in the track direction of 80 nm and a length in the track width direction. It was 0.6 μm, which is equivalent to the track pitch.

On this substrate, as shown conceptually in FIG.
The magneto-optical disk 500 can be formed by stacking a recording layer 52 made of TbFeCo, a reproducing layer 54 made of GdFeCo, a dielectric layer 56 made of silicon nitride, and a protective layer 58 made of an ultraviolet curable resin. The deposition of these layers can be easily performed by sputtering. The recording principle of the magneto-optical disk 500 will be described below. It is assumed that an initialization magnetic field is applied to the recording layer 52 in advance so that its magnetization is oriented upward (initialized). Here, of the magnetic layer portion of the recording layer 52, the coercive force Hc1 of the convex portion of the substrate, that is, the magnetic layer portion 52a on the roughened land portion is located on the concave portion of the substrate, that is, on the flat bottom. It is larger than the coercive force Hc2 of the magnetic layer portion 52b. This is because the surface roughness causes variations in the energy of the domain wall, which hinders the movement of the domain wall. Therefore, as an external magnetic field H for recording, Hc2 <H
When an external magnetic field H that satisfies <Hc1 is applied to the magneto-optical disk 500 downward, the magnetization of the portion 52a remains unchanged, whereas the magnetization direction of the portion 52b is inverted and downward. Therefore, the magnetization information is recorded in the pit corresponding to the concave portion of the substrate.

As described above, according to the present invention, rectangular pits can be formed instead of circular pits. Therefore, even in the magneto-optical disk 500 as shown in FIG. Can be increased. On the other hand, at the time of reproduction, as described in FIG. 2, a circular pit and a rectangular pit having the same length in the track direction
The rectangular pit has an advantage that the reproduction signal intensity increases because the area is larger than that of the rectangular pit. When two or more rectangular pits are present in the reproduction light spot, the magnetic characteristics of the reproduction layer 54 of the disk 500 are adjusted to adjust the magnetic super resolution (MSR).
Alternatively, reproduction by magnetic expansion reproduction (MAMMOS) disclosed by the present applicant in International Publication No. WO98 / 02878 can be performed. In particular, in magnetic expansion reproduction, a magnetic domain recorded on the recording layer 52 is transferred to the reproduction layer 54 and expanded to the size of a reproduction light spot, so that a reproduction signal with an increased signal intensity can be detected. Further, in the magnetic expansion reproduction, if the length of the magnetic domain of the recording layer 52 in the track width direction relative to the length of the magnetic domain in the track width direction is less than 1, a rectangular, crescent, or arrow feather-like shape is used. Expansion becomes easier. Therefore, it is advantageous to reproduce the magneto-optical recording medium having the rectangular pits formed on the substrate according to the present invention using the magnetic magnification reproducing method.

VI. Application to Phase Change Optical Disk The information recording medium substrate of the present invention is suitable not only for a magneto-optical disk but also for a phase change disk. FIG. 6 schematically shows a cross-sectional structure of a phase-change disk 600 using the substrate of the present invention. This disk 600 is a magneto-optical disk 5
As in the case of the substrate for 00, a substrate having surface roughness remaining on the convex portion is used. G as a phase change recording layer on the substrate 60
An eSbTe layer 62 is laminated, and further, a structure is formed in which ZnS—SiO ₂ 64 as a protective layer and an Al alloy 66 as a reflective layer are laminated.

In the case of a normal phase-change type optical disk, the recording information is carried on the amorphized portion by modulating the power of the recording light to the amorphization level and the crystallization level. On the other hand, a phase change type optical disk using the substrate of the present invention can be recorded as follows. Since the surface 50a of the land portion of the substrate is rough, crystal nuclei are likely to grow. Therefore, by irradiating the recording layer 62 deposited on the concave and convex portions on the substrate with the recording light while appropriately adjusting the recording power, only the recording layer portion 62a on the convex portion of the substrate is crystallized during cooling. And an amorphous recording mark can be formed in the other recording layer portion 62b.

The size of a recording mark recorded on the basis of the above principle is equal to that of a rectangular pit having an aspect ratio of less than 1 formed on a substrate. Therefore, as described above, the recording density of the phase-change recording medium can be improved by forming rectangular pits having a very short length in the track direction on the substrate. It is needless to say that this rectangular pit can be applied to the pre-pit in the pre-format area of the substrate, whereby the pre-format signal can also be recorded at a high density.

When reproducing a phase-change disk on which high-density recording has been performed as described above, particularly when high-density recording is performed until two or more recording marks exist in the reproducing light spot, the Japanese Journal of Applied Ph
ysics, 38, 1656-1660 (1999)
The recorded marks can be individually reproduced using a phase change super-resolution technique as disclosed in US Pat.

Embodiment 2 In this embodiment, a method of manufacturing a master according to a second embodiment of the present invention will be described with reference to FIG. A magnetic fine particle liquid was prepared by dispersing 30 parts by weight of Co ferrite fine particles having an average particle diameter of 20 nm in 70 parts by weight of isopropyl alcohol. As shown in FIG. 8A, this magnetic fine particle liquid 200
Was applied onto a glass master 19. Next, using the master exposure apparatus used in Example 1, a magnetic field was applied to a predetermined position on the master using a magnetic head. At this time, the magnetic fine particles in the magnetic fine particle liquid migrated from the magnetic head toward a magnetic field generated toward a predetermined position of the master, and an aggregate of the magnetic fine particles was formed there. The master, to which a magnetic field was applied to a desired position on the master in a predetermined pattern, was dried using a heater to evaporate alcohol. In this way, as shown in FIG. 8B, a plurality of convex portions 210 made of an aggregate of magnetic fine particles were formed on the master, and a master having a concavo-convex pattern was obtained. Convex part 2
The shape of No. 10 was a trapezoid, a height of about 0.07 μm, a length in the track direction of about 80 nm, and a track width direction of about 0.6 μm.

Next, silicon nitride was deposited by sputtering on the master 19 on which the convex portions 210 were formed so as to have a film thickness of about 10 nm. As a result, as shown in FIG. 8C, a master in which the protrusions 210 were covered with the silicon nitride film 220 was obtained. Using this master, a stamper is manufactured in the same manner as in Example 1, and a substrate for an information recording medium can be manufactured by injection molding using the stamper. As in the case of the substrate obtained in Example 1, the size of the pits of the substrate is determined by an aggregate (magnetic mark) of magnetic fine particles formed on the master. That is, since the aggregate of the magnetic fine particles can form a rectangular mark having an aspect ratio of less than 1 by using a magnetic head, such a rectangular pit can also be obtained on the substrate. Therefore, an information recording medium capable of high-density recording can be manufactured by using the substrate obtained in this embodiment.

In the second embodiment, isopropyl alcohol is used as the liquid for dispersing the magnetic fine particles. Instead, an organic solvent or oil having a suitable viscosity such as a higher alcohol can be used. Also,
Although the silicon nitride film is used as the protective film in the above example, a metal film such as Ni can be used instead. The protective film can be omitted as long as the liquid for dispersing the magnetic fine particles is a liquid that can adhere or fix the magnetic fine particle aggregate on the master after drying.

Although the present invention has been described with reference to specific embodiments, the present invention is not limited thereto, and modifications and improvements of the specific embodiments conceivable to those skilled in the art can also be included in the present invention.
For example, in the above specific example, a CD-
Although a ROM, a magneto-optical disk, and a phase change optical disk have been described as examples, the present invention can be applied to an optical disk having a recording layer containing a dye. In this type of optical disk, heat generated when recording light is applied to a recording layer causes decomposition or explosion of dye, and information is recorded by deformation of an optically identifiable substrate. In a substrate having a rough surface formed in a concave portion or a convex portion of the substrate, heat is easily accumulated in the rough surface portion. Therefore, even when the entire surface of the recording layer is irradiated with recording light, only the rough surface portion is formed. , The decomposition of the dye proceeds, whereby information can be recorded. In addition, since the size of the rough surface portion is determined by minute pits formed on the substrate and having an aspect ratio of less than 1, an extremely high-density dye-type optical disk can be provided.

The information recording medium to which the present invention can be applied is not limited to the optical recording medium exemplified in the specific examples.
The present invention can also be applied to a magnetic recording medium having emboss type prepits.

The following method is also conceivable as a modification of the second embodiment of the present invention. That is, for example, a magnetic mark pattern is formed using a magnetic head on a disk having a magneto-optical recording film or a magnetic recording film formed on a grooved substrate. Sprinkling magnetic fine particles on this disk,
The magnetic fine particles are deposited on the magnetic mark pattern to form a convex portion of the magnetic fine particles according to the pattern. Next, by forming a protective film such as silicon nitride on the disk on which the protrusions are formed, the protrusions can be fixed on the disk.

[0062]

According to the method for manufacturing a master and the master exposure apparatus of the present invention, instead of forming a photosensitive pattern by turning light on and off in accordance with the recorded information for forming pits as in the prior art, the recorded information is recorded. In order to form a photosensitive pattern in accordance with the pattern of the magnetic mark by recording the magnetic mark by reversing the polarity of the magnetic field accordingly, the photosensitive pattern is not limited to the shape and size of the exposure spot, but is rectangular and has an aspect ratio of 1. Less patterns can be formed. Therefore, it is possible to provide a master on which irregularities corresponding to pit information are formed in a line direction at high density and a substrate obtained therefrom.

The photosensitive material according to the present invention contains magnetic fine particles dispersed therein, and the magnetic fine particles can move or migrate within the photosensitive material according to an applied external magnetic field. And a master disc exposure apparatus.

The substrate according to the present invention has a rectangular pit shape,
It can be in the shape of a crescent, arrow or bar code, and its aspect ratio is less than 1, so that the pit density per unit length in the reading direction can be improved,
Thereby, the density of the information recording medium can be increased.
Further, since the substrate has a roughened surface, when the information recording medium is a phase-change optical recording medium, it can function as a site where crystal nuclei are generated, and the information recording medium is a magneto-optical recording medium. In some cases, different information can be recorded on the magnetic material existing in the roughened portion and in the non-roughened portion by utilizing the difference in coercive force. Therefore, the present invention provides a novel information recording medium capable of high-density recording.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating rectangular pits formed on a substrate of the present invention in relation to a conventional circular pit.

FIG. 2 is a diagram illustrating rectangular pits formed on a substrate of the present invention in relation to a conventional circular pit.

FIG. 3 is a diagram illustrating a schematic configuration of a master exposure apparatus of the present invention.

FIG. 4 is a top view of a magneto-optical head used in the master exposure apparatus shown in FIG.

FIG. 5 is a conceptual diagram illustrating a relationship between a magnetic mark formed on a track of a master and an exposure spot using the master exposure apparatus of the present invention.

FIG. 6 is a diagram showing a schematic structure of a cross section of a magneto-optical disk using a substrate according to the present invention cut along a track.

FIG. 7 is a diagram showing a schematic structure of a cross section of a magneto-optical disk using a substrate according to the present invention cut along a track.

FIG. 8 is a diagram illustrating a process of a method for manufacturing a master according to a second embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 17 Objective lens 19 Master disk 20 Photoresist 21 Turntable 28 Moving holder 31 Support plate 33, 35 Opening 37 Magnetic head 41 Slider 50, 60 Substrate 61 Track 62 Phase change recording layer 63 Circular pit 65, 67 Rectangular pit 80 Magnetic mark 82 Exposure Spot 200 Magnetic fine particle liquid 210 Magnetic fine particle protrusion 220 Silicon nitride protective film

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masaki Sekine 1-88 Ushitora, Ibaraki-shi, Osaka F-term in Hitachi Maxell, Ltd. (Reference) 2H097 AA03 AB06 BA06 CA17 FA06 JA03 LA20 5D075 FF20 FG17 GG07 GG16 5D121 AA02 BA01 BA05 BB02 BB08 BB21 BB38 BB40

Claims (29)

[Claims] 1. A method of manufacturing a master having an uneven pattern used for manufacturing an information recording medium substrate formed on a surface thereof, comprising coating a photosensitive material having magnetic fine particles dispersed on a flat surface of the master. Forming a magnetic mark composed of an aggregate of magnetic fine particles in a photosensitive material by applying a magnetic field to the master according to recorded information, and exposing the photosensitive material to expose the photosensitive material in accordance with the mark pattern of the magnetic mark; A method for producing a master disc, comprising exposing a photosensitive material to light and developing the exposed photosensitive material. 2. Applying a magnetic field using a magnetic head, the length of the shortest magnetic mark in the master moving direction is λ / (2
NA) (where λ is the wavelength of light at the time of exposure,
2. The method according to claim 1, wherein the magnetic mark is smaller than the numerical aperture of the objective lens used for master exposure. 3. The method for producing a master according to claim 1, wherein the exposure is performed using continuous light. 4. A method of manufacturing a master having an uneven pattern used for manufacturing an information recording medium substrate on a surface, comprising: disposing a magnetic fine particle liquid obtained by dispersing magnetic fine particles in a liquid on a flat surface of the master; And applying a magnetic field to the magnetic fine particle liquid on the master according to the recorded information to generate a magnetic mark consisting of an aggregate of magnetic fine particles in the magnetic fine particle liquid, and removing the liquid from the master to create a magnetic mark A method for manufacturing a master, comprising: forming a convex portion made of a mark on a master; and fixing the convex portion. 5. The convex portion is fixed on the master by forming a protective film on the master on which the convex portion is formed.
3. The method for producing a master described in 1. 6. A magnetic field is applied to the master while moving the master relative to the magnetic field to form a magnetic mark such that the length of the magnetic mark in the direction of movement of the master is shorter than the length in a direction perpendicular to the magnetic mark. The method of manufacturing a master according to claim 1, wherein the master is driven. 7. A master for producing a substrate for an information recording medium, comprising a plurality of projections formed from an aggregate of magnetic fine particles on a flat master. 8. The master according to claim 7, further comprising a protective film covering the projection. 9. A master exposure apparatus used for manufacturing an information recording medium substrate and exposing a master coated with a photosensitive material in a predetermined pattern, wherein a magnetic field is applied to the master according to the pattern. A light source for exposing the photosensitive material, wherein the photosensitive material is a photosensitive material in which magnetic fine particles movable by a magnetic field applied from the magnetic head are dispersed. A magnetic mark formed of an aggregate of magnetic fine particles is formed in a photosensitive material by applying an external magnetic field by a magnetic head, and the photosensitive material on which the magnetic mark is formed is exposed by a light source. Master exposure equipment. 10. The master exposure apparatus according to claim 9, wherein the magnetic head is a magnetic head used for a hard disk drive. 11. The master exposure apparatus according to claim 9, wherein the magnetic head is a magneto-optical head having a magnetic coil around or near a lens. 12. The master exposure apparatus according to claim 9, further comprising a moving device for moving the master with respect to the magnetic head and the light source. 13. The master exposure apparatus according to claim 12, wherein a magnetic head is arranged forward in the moving direction of the master, and an optical element for emitting light from a light source to the master is arranged behind. 14. The master exposure apparatus according to claim 9, further comprising a control device for controlling the magnetic head so as to apply a magnetic field according to the recording information to the master. 15. A photosensitive material in which magnetic fine particles are dispersed, wherein the magnetic fine particles can move in the photosensitive material by applying a magnetic field. 16. The magnetic fine particle is a metal selected from the group consisting of Co, Fe and Ni, an alloy containing the metal,
The photosensitive material according to claim 15, which is composed of an oxide or a nitride. 17. An information recording medium substrate in which prepits are formed in an information reading direction, wherein the length of the prepit in the information reading direction is shorter than the length of the prepit in a direction orthogonal thereto. Substrate. 18. The substrate according to claim 17, wherein the prepit is an information recording prepit or a preformat prepit. 19. The substrate according to claim 17, wherein the prepit is formed in a rectangular shape, an arrow feather shape, a crescent shape, or a barcode shape. 20. The length of the pre-pit in the information reading direction is λ / (3NA) (where λ is the wavelength of the reproduction light when reproducing the information recording medium, and NA is the reproduction light 20. The substrate according to any one of claims 17 to 19, which is shorter than a numerical aperture of a lens for condensing light thereon. 21. The substrate according to claim 17, wherein a surface of the concave portion or the convex portion of the substrate defined by the prepit is roughened. 22. The substrate is manufactured by injection molding using a stamper obtained by duplicating a master, and the master is:
A photosensitive material in which magnetic fine particles are dispersed is applied on a flat surface of a master, and a magnetic mark composed of an aggregate of magnetic fine particles is formed in the photosensitive material by applying a magnetic field to the master according to recorded information, 18. The substrate according to claim 17, wherein the substrate is a master manufactured by exposing a photosensitive material according to a mark pattern of the magnetic mark by exposing the photosensitive material and developing the exposed photosensitive material. . 23. The substrate is manufactured by injection molding using a stamper obtained by duplicating a master, and the master is provided with a magnetic fine particle liquid obtained by dispersing magnetic fine particles in a liquid on a flat surface of the master. A magnetic mark consisting of an aggregate of magnetic fine particles is generated in the magnetic fine particle liquid by applying and applying a magnetic field to the magnetic fine particle liquid on the master according to the recorded information, and the magnetic mark is removed by removing the liquid from the master. 2. A master produced by forming a convex portion on a master and fixing the convex portion.
8. The substrate according to 7. 24. An information recording medium having a substrate on which prepits are formed in the information reading direction, wherein the length of the prepit in the information reading direction is shorter than the length of the prepit in a direction orthogonal thereto. Characteristic information recording medium. 25. The information recording medium according to claim 24, further comprising at least an information recording layer on the substrate. 26. The information recording medium according to claim 24, wherein the surface of the concave portion or the convex portion of the substrate defined by the prepits is rough. 27. An optical recording medium having a magneto-optical recording medium, a phase-change optical recording medium or a dye recording layer.
27. The information recording medium according to any one of -26. 28. The information recording medium is a magneto-optical recording medium, comprising a magnetic layer directly or indirectly on a substrate, and erasing or initializing a magnetic layer located on a roughened portion of the substrate. The information recording medium according to claim 24, wherein the magnetization of the information recording medium is recorded. 29. The information recording medium is a phase change recording medium, comprising a phase change recording layer directly or indirectly on a substrate,
25. The information recording medium according to claim 24, wherein the recording layer portion located on the portion of the substrate whose surface is roughened by light irradiation is crystallized.