JP2002015474A - Method for manufacturing master disk of optical disk and optical disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a master disk of an optical disk capable of producing a high capacity optical disk substrate having a large taper angle of a groove. SOLUTION: Two photoresist films 2a, 2b are formed on a quartz substrate 1 and a groove 10 having a large taper angle is formed by using dry etching conditions vastly different from each other in etching rate. The resulting ruggedness is transferred to the substrate 1 by dry etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical disk master, and more particularly to a method for manufacturing an optical disk master suitable for high-density recording and an optical disk substrate manufactured using the master.

[0002]

2. Description of the Related Art In recent years, the amount of information handled has increased due to the development of the information society, and large-capacity storage media have been required. Under such circumstances, a 2.6 GB DVD-RAM (rewritable) storage medium has been developed as an optical disk.
Used in a wide range of fields. However, in the field of handling image information, in order to process an enormous amount of information, a larger capacity rewritable storage medium is required.
In order to respond to this, research for further increasing the capacity of optical discs is under way. 2.6 GB DVD-RA
The M substrate has a diameter of 12 cm, and a high-density technology is required to achieve a large capacity without changing the size.

As a method of increasing the density, a method of reducing the width of an L / G (Land & Groove) for recording information and increasing the linear density is generally used. At this time, since the reproducing apparatus needs to be backward compatible so that the conventional storage medium can also be reproduced, the same optical head as the conventional one is used. When recording is performed on a high-density storage medium using this optical head, the heat generated by recording reaches adjacent tracks and the L / G
Since the width is smaller, the irradiation of a part of the recording spot on the adjacent track is synergistic, and there is a problem that thermal crosstalk for erasing information on the adjacent track occurs. As a method of coping with this crosstalk, the depth of L / G is made about three times deeper than in the past, and the DG (Deep
Groove) method (see, for example, "Nikkei Electronics" 1996, 670, pp. 113-119).

FIG. 6 shows an optical disk process of the DG method.
This will be described with reference to FIG. FIG. 6A shows a quartz substrate 61 polished with high precision. On this quartz substrate 61, FIG.
A photoresist film 62 is applied as shown in FIG. In the exposure step, as shown in FIG. 6C, a spiral groove or pit is exposed using an optical disk exposure device. The laser beam 63 is condensed by the lens 64 to form a laser spot, and the photoresist film 62 on the rotating quartz substrate 61 is irradiated with the spot of the Ar laser 63 being focused and a latent image 65 is formed. In the optical system of the Ar laser beam 63, a cylindrical lens or a rectangular or elliptical slit is provided in the optical path to make the laser spot elliptical. When exposure is performed with this laser spot, wider grooves and pits can be exposed than when there is no cylindrical lens or slit. Hereinafter, formation of the groove will be described.

FIG. 6D shows a developing step, in which the latent image 65 forms an uneven groove 66 by the developing process, and the unexposed photoresist becomes a land 67. Groove 66 and land 6
7 have the same dimensions. Thereafter, washing and drying are performed. FIG. 6E shows an etching step. After the heat treatment, the etching gas 68 is dried in a dry etching apparatus.
Etching is performed by a chemical reaction with The groove 66 is formed on the surface of the quartz substrate 61 by etching. That is, the groove 66 is transferred to the groove 69. On the other hand, since the etching of the land 67 is stopped by the photoresist film, the surface of the quartz substrate 61 therebelow becomes the land 70.
The etching is controlled so that the depth of the groove 69 becomes three times the conventional depth. The taper angle of the groove 69 can be different from that of the groove 66 by changing the etch rate ratio between the quartz substrate 61 and the photoresist film 62. After that, the remaining photoresist film 62 is removed, and a DG master 71 as shown in FIG. An Ni stamper is manufactured from the DG master 71, and an optical disk substrate is manufactured from the Ni stamper by resin molding.

[0006]

As described above, in the DG method, an L / G master having a depth approximately three times as large as the conventional one and a large taper angle is manufactured by using the etching method. DG
When a recording film is formed on an optical disk substrate made from the master and recording is performed in the groove, the recording film becomes thin due to the large taper angle of the groove and the heat conduction is reduced, and the heat conduction to adjacent tracks is reduced. Crosstalk is reduced. To further reduce thermal crosstalk, it is necessary to increase the taper angle of the groove 69 formed on the DG master. To this end, it is effective to increase the taper angle of the groove 66 formed in the photoresist film 62 and to increase the etch rate ratio between the quartz substrate 61 and the photoresist film 62.

[0007] The taper angle of the groove 66 formed in the photoresist film 62 is determined by the relationship between the intensity distribution of the spot of the Ar laser 63 and the photosensitive curve of the photoresist film 62. The intensity distribution of the spot has a direction in which the taper angle increases as the wavelength of the Ar laser 63 is shortened. However, it is difficult to shorten the wavelength to less than 351 nm, and there is a limit to increasing the taper angle. To improve the photosensitive curve of the photoresist film 62, it is necessary to wait for the development of a new photoresist with high sensitivity.

[0008] An improvement in the etch rate ratio is provided by optimizing the etching conditions. However, in dry etching, if the etching rate of the quartz substrate 61 is increased, the etching rate of the photoresist film 62 is also increased, so that a significant improvement in the etch rate ratio cannot be expected.
Further, when the groove 69 is formed in the quartz substrate 61 under the etching condition of the maximum etch rate ratio, the temperature of the quartz substrate 61 during the etching is not stable, so that the maximum etch rate ratio cannot be stably maintained. Therefore, the groove 69 can be stably formed.
There is a disadvantage that the taper angle cannot be increased. In the conventional method, the maximum taper angle of the groove 69 formed in the quartz substrate 61 is about 80.
°, and in order to develop an optical disk substrate having a larger capacity without thermal crosstalk, it is necessary to set the taper angle to 80 ° or more.

As described above, in the conventional optical disk manufacturing process, several problems are encountered when DG is used for a large-capacity optical disk substrate. In order to form a groove having a large taper angle, it is necessary to study a new photoresist with high sensitivity and to study the optimization of dry etching conditions in consideration of the type of etching gas, but this is difficult at present.

The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to provide a method for stably and easily manufacturing an optical disk master on which grooves and pits having a large taper angle are formed. Another object of the present invention is to provide a method for manufacturing an optical disk capable of high-density recording using the optical disk master.

[0011]

The object of the present invention is to form two layers of photoresist films having different etch rates on a quartz substrate and to etch the upper photoresist film having grooves and pits to form a lower photoresist film. This is achieved by forming a large taper angle by transfer and then performing etching to transfer grooves or pits having a target taper angle to the quartz substrate.

That is, in the method of manufacturing an optical disk master according to one embodiment of the present invention, a step of forming a Si-free photoresist film on a quartz substrate and hard baking, and forming a Si-containing photoresist film on the Si-free photoresist film , A step of exposing a groove and / or pit pattern using a laser beam, a step of forming a concavo-convex shape reflecting the exposure pattern on a Si-containing photoresist film by development, and a dry etching using an O ₂ gas. Transferring the concavo-convex shape of the Si-containing photoresist film to a Si-free photoresist film by dry etching using a CF ₄ gas to transfer the concavo-convex shape of the Si-containing photoresist film onto a quartz substrate; Membrane and S
removing the i-free photoresist film.

[0013] The method of manufacturing an optical disk master according to one aspect of the present invention further comprises a step of forming a first photoresist film from which photosensitivity has been removed on a quartz substrate, and a step of forming a second photoresist film on the first photoresist film. Forming a film;
Forming a concavo-convex pattern on the photoresist film, and etching the second photoresist film under the condition that the etch rate of the first photoresist film is 10 times or more the etch rate of the second photoresist film to form the concavo-convex pattern on the second photoresist film. The method is characterized by including a step of transferring to a first photoresist film and a step of transferring an uneven pattern formed on the first photoresist film to a quartz substrate by etching. Etching is performed under the condition that the etch rate of the first photoresist film is 10 times or more the etch rate of the second photoresist film, thereby forming an uneven pattern having a taper angle of about 85 ° or more in the first photoresist film. be able to.

A method of manufacturing an optical disk substrate according to the present invention includes a step of manufacturing a Ni stamper from an optical disk master manufactured by the above method, and a step of manufacturing an optical disk substrate by injection molding using the Ni stamper. And According to the method of the present invention, the taper angle of the grooves or pits formed on the optical disk master is stably set to an angle of about 90 ° larger than the conventional maximum taper angle of about 80 °, for example, an angle of 85 ° or more. Can be. By using this optical disk master, it is possible to stably manufacture an optical disk substrate having a taper angle of a groove or a pit of about 90 °, for example, 85 ° or more and suitable for a large capacity without thermal crosstalk. .

[0015]

Embodiments of the present invention will be described below with reference to the drawings. An optical disk is manufactured through a master disk manufacturing process, a stamper manufacturing process, an injection molding process, and a film forming process. FIG. 1 is a schematic diagram illustrating an example of a master production process according to the present invention. As shown in FIG. 1A, a positive photoresist film 2 is formed on a quartz substrate 1 whose surface is polished with high precision.
a is formed. Here, F is used as the photoresist film 2a.
Hi610U (Fuji Film Ohlin Co., Ltd.) was used, and the film thickness was 0.5 μm. The photoresist film 2a was hard baked at 200 ° C. so as not to be exposed when exposed by the optical disk exposure apparatus. Next, as shown in FIG. 1B, a photoresist film 2b containing Si was formed on the hard-baked photoresist film 2a, and a heat treatment at 90 ° C. was performed. Fi-SP (Fuji Film Ohlin) was used for the photoresist film 2b, and the film thickness was 0.2 μm.

Next, as shown in FIG. 1C, pattern exposure was performed on the photoresist film 2b using an optical disk exposure apparatus. The quartz substrate 1 having two photoresist films 2a and 2b formed on its surface is rotated to converge the Ar laser beam 3 at the focal position of the converging lens 4 to form a minute spot, and the focal position is set on the photoresist film 2b. Under the control, the latent image 5 is formed by exposing the grooves and pits. The pits having different lengths are irradiated by controlling ON / OFF of the Ar laser light 3 by an optical modulator. The groove can be illuminated by increasing the ON time of the optical modulator. The ON time of the optical modulator is controlled depending on the use of the optical disk substrate.

Thereafter, development and drying were performed. The result is shown in FIG. The latent image 5 formed on the upper photoresist film 2b is dissolved by development to form a groove 6, and the unexposed portion forms a land 7. However, since the lower photoresist film 2a has no photosensitivity and no latent image is formed at a portion corresponding to the latent image 5 of the upper photoresist film 2b, no irregularities are formed on the lower photoresist film 2a.

[0018] Next, when the dry etching to the etching gas 8 using O _2, as shown in FIG. 1 (e), a groove groove 6 formed on the upper layer of the photoresist film 2b is the lower layer of the photoresist film 2b Transferred as 9 The photoresist film 2b is a photoresist containing Si, and has a property that it is hard to be etched by dry etching with O ₂ . Therefore, the etch rate of the photoresist film 2b is smaller than that of the photoresist film 2a, and an etch rate ratio of about 50 is obtained. This is because when the thickness of the photoresist film 2a is etched, the thickness of the photoresist film 2b is 0.01 μm.
It means that only the following film thickness is etched, and the groove 6
Will hardly change. That is, the etching proceeds in the depth direction, and the lower photoresist film 2b is formed.
The taper angle of the groove 9 formed at about 90 ° was obtained.

Further, as shown in FIG. 1F, when dry etching is performed using CF ₄ as an etching gas 10, the grooves 9 are transferred to the quartz substrate 1 as grooves 11. Also in the etching at this time, since the etch rate of the quartz substrate 1 was higher than that of the photoresist film 2a, the taper angle of the groove 11 was about 90 °. Etching gas 1
A similar result can be obtained with a gas in which CHF ₃ is mixed with CF ₄ as 0.

[0020] Thereafter, as shown in FIG. 1 (g), a taper angle of about 90 ° of performing ashing process using O ₂ as an etching gas 12 photoresist film 2a and the photoresist film 2b is removed groove 11 Optical disk master 15 was obtained. According to the method of the present invention, the etch rate ratio between the photoresist film 2b and the photoresist film 2a can be as large as about 50 even when the etching conditions fluctuate. Therefore, the taper angle of the groove 9 formed on the master optical disc master is stable. About 90 °.

FIG. 2 shows the etch rate ratio of the two photoresist films (etch rate of the lower photoresist film 2a / etch rate of the upper photoresist film 2b) when dry etching is performed in the step of FIG. 1 (e). FIG. 9 is a diagram illustrating a result of simulating the relationship between the taper angle of a groove formed in a lower photoresist film 2a and a lower layer. In FIG.
The solid line shows the result when the taper angle of the groove formed in the upper photoresist film 2b is 40 °, and the dashed line shows the result when the taper angle of the groove formed in the upper photoresist film 2b is 50 °, and the broken line. Shows the results when the taper angle of the groove formed in the upper photoresist film 2b is 60 °.

FIG. 2 shows that the taper angle of the groove transferred to the lower photoresist film 2a by etching increases as the etch rate ratio increases. When the etch rate ratio is set to 10 or more, the taper angle of the groove transferred to the lower photoresist film 2a can be set to approximately 85 ° or more. For example, when the etch rate ratio is set to 20, the groove transferred to the lower photoresist film 2a can be set. Is approximately 87 ° to 88 °. Further increase the etch rate ratio to about 4
When it is set to 0, the taper angle of the groove transferred to the lower photoresist film 2a becomes substantially 90 °.

FIG. 3 is a schematic diagram for explaining a process for producing a stamper from the master produced in the process of FIG. First,
As shown in FIG. 3A, a conductive film 31 for an electrode for electrolytic plating is formed on the master 15. Next, as shown in FIG. 3B, electrolytic plating (Ni
Plating) to obtain a Ni plating film 32 having a thickness of about 300 μm.
To form Then, as shown in FIG. 3C, a wedge is inserted into the surface of the glass substrate to perform peeling. Thus, a stamper 35 having a normal surface as shown in FIG. 3D is obtained.

FIG. 4 is a schematic diagram for explaining a process of manufacturing an optical disk substrate by injection molding using the stamper. As shown in FIG. 4A, the stamper 35 was set on a mold 41 of an injection molding machine. Next, as shown in FIG. 4B, a resin 43, here, PC (Polycarbonate) is injected between the stamper 35 and the pressure plate 42, and pressurized at a pressure of several tons as shown in FIG. 4C. . Then, as shown in FIG. 4D, the pressure was stopped and the PC board was taken out. Thus, an optical disk substrate 45 having grooves and pits formed on the surface was obtained.

FIG. 5 is an explanatory diagram of a process of manufacturing an optical disk using an optical disk substrate. In the manufacturing process of the optical disk, a film 51 is formed on an optical disk substrate 45 made of PC as shown in FIGS. The film forming material differs depending on the use of the optical disk substrate. CD and DVD-ROM
In this case, Al is used. CD-R, MO, DVD-RA
For M, minidisc, etc., a recording material is deposited. Then, as shown in FIG. 5C, a polymer film 52 is formed for protecting the surface. Thus, the optical disk 55 is completed.

According to the present invention, an optical disk substrate having a groove having a depth of about 70 nm, which is almost the same as the groove of the conventional substrate, is manufactured, and a GeSbTe recording film having a thickness of 10 to 3
When 0 nm was formed and thermal crosstalk was evaluated, better results were obtained than the conventional substrate.

As described above, according to the present invention, by dry-etching two layers of photoresist in which the lower layer etching rate is higher than the upper layer etching rate, a taper angle larger than that formed by a conventional optical disk exposure apparatus is obtained. Grooves and pits can be formed in the photoresist film. Further, when dry etching is performed on the quartz substrate using the photoresist film as a mask, it is possible to obtain an optical disk master in which grooves and pits having a larger taper angle are stably formed. Also, by using a stamper manufactured from this optical disk master, it is possible to manufacture an optical disk substrate for a large capacity in which the taper angle of the groove is large and crosstalk is reduced.

[0028]

According to the present invention, an optical disc master having a large groove taper angle can be manufactured stably and easily.
By using the optical disk master, an optical disk compatible with a high recording density can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a master production process according to the present invention.

FIG. 2 is a diagram showing a relationship between an etch rate ratio of two photoresist films and a taper angle of a groove formed in a lower photoresist film.

FIG. 3 is a schematic diagram illustrating a process of manufacturing a stamper from a master.

FIG. 4 is a schematic diagram illustrating a process of manufacturing an optical disk substrate using a stamper.

FIG. 5 is an explanatory diagram of a process of manufacturing an optical disk using an optical disk substrate.

FIG. 6 is a diagram showing a manufacturing process of an optical disc master according to a DG method as a conventional technique.

[Explanation of symbols]

1. Quartz substrate, 2a ... Si-free photoresist film, 2b
... Si-containing photoresist film, 3 ... Ar laser beam, 4 ... converging lens, 5 ... latent image, the groove 6 ... photoresist film, 7 ... photoresist film lands, 8 ... O ₂ etching gas, 9 ...
Grooves of Si-containing photoresist layer, 10 ... CF ₄ etching gas, 11 ... groove of the quartz substrate, 12 ... _{O 2} etching gas, 15 ... optical disc master, 31 ... conductive film, 32 ... Ni
Plating film, 35: stamper, 41: mold of injection molding machine,
42 pressure plate, 43 resin, 45 optical disk substrate, 5
DESCRIPTION OF SYMBOLS 1 ... film | membrane, 52 ... polymer film, 55 ... optical disk, 61 ... quartz substrate, 62 ... photoresist film, 63 ... Ar laser beam,
64 ... converging lens, 65 ... latent image, 66 ... groove of the photoresist film, 67 ... photoresist film lands, 68 ... CF ₄ etching gas, 69 ... groove of a quartz substrate, 70 ... a quartz substrate lands, 71 ... optical disc master

Continued on the front page (72) Inventor Motoyasu Terao 1-280 Higashi Koigabo, Kokubunji-shi, Tokyo F-term in Central Research Laboratory, Hitachi, Ltd. 5D121 AA02 BA01 BA03 BB02 BB03 BB08 BB32 BB33 CA05 DD05 GG02

Claims (3)

[Claims] 1. A step of forming a Si-free photoresist film on a quartz substrate and hard baking; a step of forming a Si-containing photoresist film on the Si-free photoresist film; Or a step of exposing a pattern of pits; a step of forming a concavo-convex shape reflecting the exposure pattern on the Si-containing photoresist film by development; and a step of forming the concavo-convex shape of the Si-containing photoresist film by dry etching using O ₂ gas. Transferring to an Si-free photoresist film, transferring the uneven shape of the Si-free photoresist film onto a quartz substrate by dry etching using CF ₄ gas, and removing the Si-containing photoresist film and Si-free photoresist film. And a method for producing a master optical disc. 2. A step of forming a first photoresist film from which photosensitivity has been removed on a quartz substrate; a step of forming a second photoresist film on the first photoresist film; and a step of forming the second photoresist film. Forming a concavo-convex pattern on the film, and etching under conditions that the etch rate of the first photoresist film is 10 times or more the etch rate of the second photoresist film to form the concavo-convex pattern on the second photoresist film. A method of manufacturing a master optical disc, comprising: a step of transferring to the first photoresist film; and a step of transferring an uneven pattern formed on the first photoresist film to the quartz substrate by etching. 3. A process for producing a Ni stamper from an optical disc master produced by the method for producing an optical disc master according to claim 1 or 2, and a process for producing an optical disc substrate by injection molding using the Ni stamper. A method for manufacturing an optical disk substrate, comprising: