JP3682763B2 - Manufacturing method of optical disc - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk manufacturing method, and more particularly to an optical disk manufacturing method having prepits and pregrooves having different depths.
[0002]
[Prior art]
A so-called write-once optical disk that can be written on the user side has a structure in which a recording layer is provided on an optical disk substrate on which prepits and pregrooves are formed in advance. The depth of the prepit is a depth in the vicinity of λ / 4n where the modulation degree of the reproduction signal obtained from the prepit is maximized. On the other hand, the depth of the pregroove is a depth in the vicinity of λ / 8n at which the modulation degree of the tracking signal obtained from the pregroove is maximum. Here, λ is the wavelength of the reproduction laser beam, and n is the refractive index of the substrate.
[0003]
A writable optical disc having prepits and pregrooves having different depths as described above is manufactured by obtaining a replica (replica) of an optical disc master having prepits and pregrooves similar to the optical disc substrate. As shown in FIGS. 1 and 2, in the production of an optical disc master, first, an unexposed master in which a photoresist layer 2 is formed on a glass substrate 1 is created.
[0004]
Next, the photoresist layer 2 is exposed by irradiating the unexposed master with an intensity-modulated laser beam. For example, when the pregroove 21 is formed, the laser beam 10a having a low intensity is irradiated. Then, the surface layer vicinity (depth d1) of the photoresist layer 2 is exposed. On the other hand, when the prepit 22 is formed, the laser beam 10b having a stronger intensity than the laser beam 10a is irradiated. The laser beam 10b is deeper in the direction of the glass substrate 1 (depth d2, d2> d1) than when the photoresist layer 2 is irradiated with the laser beam 10a, and exposes the photoresist layer 2. .
[0005]
When the exposed master is developed after the irradiation of the laser beams 10a and 10b, the exposed portion of the photoresist layer 2 by the laser light is removed, and an optical disc master can be created.
Furthermore, when a resin molding is performed using a stamper in which the surface of the optical disk master is transferred by nickel electroforming or the like, an optical disk substrate that is a replica of the optical disk master can be produced.
[0006]
[Problems to be solved by the invention]
By the way, the light intensity distribution of the laser light has a Gaussian distribution having the maximum intensity at the center of the beam (see FIG. 1). As described above, the maximum intensity in the light intensity distribution 5 of the laser beam 10a is lower than the maximum intensity in the light intensity distribution 6 of the laser beam 10b. Therefore, the diameter 5b of the region 5a where the photoresist layer 2 is exposed by the laser beam 10a (that is, the width of the pregroove 21) is the diameter 6b of the region 6a where the photoresist layer 2 is exposed by the laser beam 10b. (That is, the width of the pre-pit 22). Accordingly, when the pregroove 21 (depth d1) and the prepit 22 (depth d2) having different depths are formed, the width 5b of the pregroove 21 becomes narrower than the width 6b of the prepit 22.
[0007]
In this case, if the pregroove 21 is formed by meandering periodically, the wobble signal from the pregroove 21 leaks into the reproduction signal from the prepit 22 and the reproduction signal characteristics deteriorate. .
The present invention has been made to solve the above-described problems, and it is an object of the present invention to provide a method of manufacturing an optical disc capable of forming prepits and pregroups having a predetermined width.
[0008]
[Means for Solving the Problems]
Optical disc manufacturing method according to the present invention is a manufacturing method of an optical disc having a different pre-pits and pre-grooves in depth with each other, forming a photoresist layer on a glass substrate, the glass substrate and the photoresist layer to each other A step of irradiating the photoresist layer with a laser beam modulated in intensity as a spot while relatively moving, a step of developing the photoresist layer, and a heat treatment step of heating the photoresist layer, The step of irradiating the laser beam includes a step of making the shape of a spot elliptic by passing the laser beam through a cylindrical lens and an objective lens, and the minor axis direction of the ellipse is the laser beam with respect to the glass substrate. It is characterized by being substantially parallel to the moving direction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
An optical disk manufacturing method according to the present invention will be described in detail with reference to the drawings.
As shown in FIG. 3, the unexposed master 3 is obtained by forming a photoresist layer 2 having a thickness of about 800 to 1500 mm on a glass substrate 1. First, a glass substrate 1 whose surface is polished and cleaned is prepared, and a positive photoresist is applied on the glass substrate 1. The photoresist is, for example, a positive photoresist “TSMR-V3” manufactured by Tokyo Ohka Kogyo Co., Ltd. A solution obtained by dissolving this in an organic solvent is applied on the glass substrate 1 by spin coating, and then heat-treated (prebaked) at a temperature of about 80 ° C.
[0010]
As shown in FIGS. 4 to 6, two types of laser beams 11a and 11b having different light intensities are irradiated from above the unexposed master 3 to form latent images of the pregroove 21 and the prepit 22, respectively. The light intensity of the laser beam 11a is such an intensity that the photoresist layer 2 can be partially exposed to form a latent image portion of the pregroove 21 having a depth d1 shallower than the depth d2 of the prepit 22. . The laser beam 11b has a higher light intensity than the laser beam 11a and exposes the photoresist layer 2 to form a latent image portion of the prepit 22 having a depth d2 deeper than the depth d1 of the pregroove 21. obtain.
[0011]
In particular, as shown in FIG. 5, it is selected whether the laser light irradiated to the unexposed master 3 is laser light 11a or laser light 11b. According to this selection, a command from the controller 12 is transmitted to the optical modulator 13. The laser light 11 ′ emitted from the laser light source 11 is adjusted in intensity to a light intensity corresponding to the laser light 11a or the laser light 11b after passing through the light modulator 13 after the spot size is adjusted by the lens 14. .
[0012]
The intensity-modulated laser beam 11 ′ is converted into an elliptical spot shape by the cylindrical lens 15. Details of this beam will be described later. The laser beam 11 ′ whose spot has been converted into an elliptical shape is condensed on the unexposed master 3 by the condenser lens 16 to expose the unexposed master 3. In particular, as shown in FIG. 4, in the aforementioned elliptical spot in the laser beam 11a or laser beam 11b irradiated to the unexposed master 3, the light intensity distribution in the major axis direction is as shown in distributions 7 and 8, respectively. The light intensity distribution has a uniform light intensity near the center of the spot. The laser beam intensity capable of exposing the photoresist 2 is elliptical regions 7a and 8a corresponding to the laser beam 11a or the laser beam 11b, respectively. Here, the difference between the widths 7b and 8b in the major axis direction of the elliptical regions 7a and 8a is the same as the width of the same region after intensity modulation in the laser light having the conventional Gaussian distribution described above by adjustment by the condenser lens 16 . Compared to the difference (that is, the difference between the diameter 5b and the diameter 6b in FIG. 1), it can be made smaller. In addition , the width of the latent image portion corresponding to the pregroove 21 in the photoresist layer 2 can be made wider than before.
[0013]
In the irradiation of the laser light onto the unexposed master 3, the laser light is moved in the radial direction of the master relative to the unexposed master 3 while the unexposed master 3 is rotated by synchronization means (not shown). It is. That is, the scanning direction of the laser beam is parallel to the minor axis direction A of the elliptical regions 7a and 8a as described above, that is, the minor axis direction of the elliptical spot of the laser beam 11a or the laser beam 11b.
[0014]
In particular, as shown in FIG. 6, after the exposure of the photoresist layer 2, development processing is performed using an alkaline developer. The normality of the alkali developer is about 0.2 to 0.5N, preferably about 0.2 to 0.3N. Through this process, the latent image portion of the pregroove 21 exposed by the laser beam 11a and the latent image portion of the prepit 22 exposed by the laser beam 11b are removed.
[0015]
As shown in FIG. 7, after completion of development using an alkali developer, heat treatment (post-bake) is performed at a temperature slightly higher than the melting point of the photoresist. For example, in the case of the above-described photoresist, the heat treatment is performed at a high temperature of 100 ° C. to 150 ° C., preferably 110 ° C. to 130 ° C. This high temperature heat treatment step is particularly preferable because the edge portion 21 'of the pregroove 21 is smoothed, and the gently wide pregroove 21 can be formed.
[0016]
As described above, the photoresist layer is exposed with the laser beam having a wide beam spot shape in the direction orthogonal to the scanning direction of the laser beam, and after developing the photoresist layer, the heat treatment is performed at a high temperature, thereby deepening the depth. When forming pregrooves and prepits having different thicknesses, the width of the shallow pregroove can be increased.
[0017]
By the way, the optical disc master obtained after the heat treatment (post-bake) is used for producing a stamper by a nickel electroforming method or the like. By performing resin molding using this stamper, an optical disk substrate in which such an optical disk master is duplicated can be produced. On the substrate on which prepits and pregrooves are formed, a dye recording film, a phase change recording film, and the like are provided, and an optical disc on which information can be recorded on the user side is created, but this is not described in detail here.
[0018]
【The invention's effect】
According to the present invention, an optical disk having excellent reproduction signal characteristics can be formed.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a state where a conventional unexposed master is irradiated with a laser beam.
FIG. 2 is a cross-sectional view and a plan view of a conventional optical disc master in a track direction.
FIG. 3 is a cross-sectional view of an unexposed master disc obtained by the method of the present invention.
FIG. 4 is a cross-sectional view showing a state where an unexposed master is irradiated with laser light in the method of the present invention.
FIG. 5 is a diagram of an apparatus for irradiating laser light in the method of the present invention.
FIG. 6 is a sectional view of the master before heat treatment (post-bake) in the method of the present invention.
FIG. 7 is a cross-sectional view of the master after heat treatment (post-bake) in the method of the present invention.
FIG. 8 is a cross-sectional view and a plan view in the track direction of a master disk obtained by the method of the present invention.
[Explanation of main part codes]
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Photoresist layer 3 Unexposed master 5, 6, 7, 8 Light intensity distribution
10a, 10b, 11a, 11b Laser light
11 Laser light source
12 Controller
13 Optical modulator
14, 16 lenses
15 Cylindrical lens
21 Pregroove
22 Prepit

Claims (2)

A method of manufacturing an optical disc having prepits and pregrooves having different depths, the step of forming a photoresist layer on a glass substrate, and the photo substrate while moving the glass substrate and the photoresist layer relative to each other. irradiating a laser beam intensity-modulated in the resist layer as a spot, a step of developing the photoresist layer, wherein the heat treatment step of heating the photoresist layer, the step of irradiating the laser beam said laser Including a step of making the shape of a spot elliptic by passing a beam through a cylindrical lens and an objective lens, the minor axis direction of the ellipse being substantially parallel to the moving direction of the laser beam relative to the glass substrate An optical disc manufacturing method characterized by the above.  2. The method of manufacturing an optical disk according to claim 1, wherein the heat treatment step is a step of heating to a temperature equal to or higher than a melting point of the photoresist layer.

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