JPH10241213A - Production of stamper for optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a stamper capable of producing an optical disk of a low noise level. SOLUTION: The surface of a glass master disk 10 coated with a photoresist 11 is irradiated a light beam 3, by which guide groove patterns or very small rugged signal patterns are recorded thereon. These recording patterns are developed to expose the surface of the glass master disk 10 and the surface is subjected to reactive ion etching(RIE) down to a desired depth with the non- developed surface as a mask, by which the guide grooves or the very small raggedness is formed. The residual photomask is removed to form a glass master 20. The metallic stamper 21 is manufactured by forming and Ni conductive layer 13 and an Ni electroforming layer 14 on the surface of this glass master 20. The stamper 21 is peeled from the glass master 20.

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 information recording medium, and more particularly to a method for injection molding an information recording medium such as a video disk, a digital audio disk, a write-once disk and a rewritable disk. The present invention relates to a method for manufacturing a stamper used as a mold.

[0002]

2. Description of the Related Art Optical discs capable of storing high-density data and capable of processing information at high speed have attracted attention as audio and image applications and computer memories. Diameter 5.
Optical discs such as 25-inch and 3.5-inch optical discs have a magneto-optical type or phase-change type that allows information to be rewritten.
It has been standardized by the O standard, and it is expected that its spread to the market will be further accelerated in the future.

Recently, standards for DVDs (Digital Video Discs) such as the SD standard have been solidified.
The application of optical disks to the multimedia field is expected to be even more promising.

In such an optical disk, as shown in FIG. 2, a guide for guiding a light beam 3 from a pickup 2 of a recording / reproducing apparatus to a disk substrate 1 along information, that is, a guide for tracking is provided with concave and convex. It is formed spirally from the inner circumference to the outer circumference of the disk. This groove is called a guide groove. The tracking guide will be described in detail. As defined in the ISO standard, a portion 4 that is concave when viewed from the pickup 2 side, that is, a portion that is far away is called a land. On the other hand, the protruding portion 5, that is, the portion that becomes close, is called a groove.
The distance from the center of the land 4 to the center of the adjacent land 4 is called a track pitch P. Generally, the groove 5 has a depth d of 50 nm, a width W of 0.4 to 0.6 μm, and a track pitch P of 1.4 μm.

Recently, there has been reported an optical disk having a track pitch P of 1.1 μm and a narrow track pitch in order to enable recording of higher-density information. However, in the case of an optical disk, for example, the wavelengths 630-6
80 nm semiconductor laser and numerical aperture (NA) 0.5
Conventional pickup 2 with an objective lens of ~ 0.6
If the track pitch P is smaller than 1.1 μm, the influence (optical crosstalk) on the information written on the adjacent track becomes extremely large, and the tracking error signal required for tracking becomes extremely small, so that accurate information is obtained. There have been problems such as difficulty in tracking.

In the case of a recordable optical disk, there is another problem that when writing or erasing data on a track, data on an adjacent track is also erased.
That is, since magneto-optical disks and phase-change disks are thermal recordings in which the temperature of the disk is raised by laser light, the smaller the distance between adjacent tracks, the greater the heat diffusion to adjacent tracks. Therefore, when writing or erasing information on a track, information written on an adjacent track is erased. This is called thermal crosstalk or cross erase. In particular, in a land / groove recording method in which information is recorded on both lands and grooves in order to reduce the track pitch, it is easily affected by cross-erase, and it is important to control the cross-erase at the time of repetitive recording many times. In the conventional optical disk, the width of the land and the groove in which such cross-erase poses a problem is limited to about 0.7 μm for both the magneto-optical type and the phase change type, which makes it difficult to further narrow the track. ing.

Accordingly, the present inventors have previously proposed an optical disk in which the depth of the guide groove is increased in order to reduce cross-erase. That is, in this optical disc, the heat transfer distance to the adjacent track is increased by increasing the step due to the groove, and the cross erase resistance is improved. As a result, a conventional land / groove recording type optical disk having a groove depth of 40 to 90 nm can be made deeper. For example, if the groove depth is 100 nm or more, the track pitch P can be made 0.7 μm or less.

FIG. 3 shows a method of manufacturing such a conventional optical information recording medium. In this method of manufacturing a recording medium, first, a primer such as a silane coupling agent is applied to the surface of a mirror-polished glass master 10 and then a photoresist 11 is applied and dried (a). Thereafter, a signal pattern is exposed and recorded by a light beam 3 such as an Ar laser beam, a He-Cd laser beam, an electron beam, an ultraviolet ray, and a far ultraviolet ray in accordance with a guide groove, ROM information, preformat information, and the like. Next, development is performed to remove exposed or unexposed portions (b). A positive type photoresist is known as the photoresist 11 that dissolves the exposed portion, and a negative type photoresist is known as the photoresist that removes the unexposed portion, and can be used as needed. Thus, the recording signal is formed so as to be a concave signal, and the glass master 12 is obtained.
A conductive film 13 of Ni or the like is formed on the surface of the glass master 12 by a method such as electroless plating and sputtering (c).
After the conduction treatment, a Ni electroformed layer 14 is further formed thereon by an electroforming method (d). Then, the Ni electroformed layer 14 is peeled from the glass master 10 to produce a metal stamper 15 having a convex recording signal (e). Finally, the remaining resist is removed by oxygen plasma or a solvent, etc.
Is completed. Using this stamper 15, an optical disk substrate (so-called replica) 17 having a concave recording signal is replicated by an injection molding method (f) using a synthetic resin 16 such as polycarbonate or a 2P method using an ultraviolet curable resin ( g). In the injection molding method, a synthetic resin 16 melted at a high temperature is injected under pressure into a mold to produce a replica. On the other hand, in the method using an ultraviolet curable resin, a replica is produced by applying an ultraviolet curable resin to a mold, pressing a glass or synthetic resin substrate, and irradiating ultraviolet rays to cure the ultraviolet curable resin. After this,
An optical disk is formed by forming a metal reflective film such as aluminum or a magnetic film on the recording signal surface of the optical disk substrate 17.

[0009]

As described above, since the replica disk, that is, the optical disk substrate 17 is manufactured using the stamper 15, the quality of the disk depends on the stamper 15. is not. Therefore, it is very important how to produce a high quality stamper. However, when the stamper 15 is manufactured by a conventional manufacturing method, an optical disk substrate 17 is manufactured from the stamper 15, and data is recorded and reproduced on the optical disk substrate, as shown by a broken line L1 in FIG. It has been found that the unrecorded noise has increased greatly over the period. Further, it was found that this tendency was particularly large in the case where the unevenness of the groove was 100 nm or more. Since such unrecorded noise occurs even when data is not recorded on the disk, the conditions in the substrate manufacturing process were rechecked and improved, but could not be reduced further.

Then, when the stamper 15 as the master of the optical disk substrate 17 was observed with a scanning electron microscope,
It was found that the wall surface of the groove was rougher than that having a lower step. Considering the pitch interval of the unevenness on the groove wall surface and the frequency of the noise, it is considered that the cause of the noise is due to the surface roughness of the groove wall surface.

As described above, the conventional method of manufacturing a stamper for an optical disc uses the Ni
Such a metal is plated by an electroforming method to form an electroformed layer 14 and then peeled off from the glass master 10 to produce a stamper 15. Therefore, in the case of a normal stamper manufacturing process, since metal is directly laminated on the photoresist pattern, it is no exaggeration to say that the quality of the photoresist pattern determines the quality of the stamper itself. In other words, it can be said that the surface roughness of the wall surface of the stamper, which is considered to be a cause of noise, has already been determined when the groove pattern of the photoresist 11 is formed. However, the surface roughness of the groove wall surface of the resist pattern has been reduced by selecting the photoresist material, optimizing the laser cutting conditions and the developing conditions, etc. It is difficult to control and the exposed area of the wall surface is large, so that the noise level has not reached a sufficiently acceptable noise level because the wall surface can be seen when reproduced with an optical head.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method of manufacturing a stamper for an optical disk which enables the manufacture of an optical disk having a low noise level. is there.

[0013]

In order to achieve the above object, the present invention provides a process of irradiating a glass master coated with a photoresist with a light beam to expose and record a guide groove pattern or a fine uneven signal pattern. And developing the recording pattern to expose the surface of the glass master, and forming a guide groove or minute irregularities on the surface of the glass master by reactive ion etching to a desired depth using the non-developed surface as a mask; Removing a residual photomask to form a glass master, forming a conductive film on the surface of the glass master, plating a metal on the conductive film to form a metal stamper, Separating the metal stamper from the glass master. Further, the present invention is characterized in that the glass master is quartz. Further, the present invention is characterized in that the etching depth of the glass master is 100 nm or more.

In the present invention, reactive ion etching etches a glass portion of a glass master disk very sharply compared to a polymer such as a photoresist. Therefore, a groove having a lower wall surface roughness and a larger wall angle than the photoresist pattern can be formed. If the wall angle is large, it is difficult to see the wall when the groove is reproduced by the magneto-optical head, and noise due to the surface roughness of the wall can be reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings. FIG. 1 is a process chart showing a stamper manufacturing method according to the present invention. In the manufacturing method according to the present invention, the following steps are performed: a step of irradiating a light beam 3 onto a glass master 10 coated with a photoresist 11 to expose and record a guide groove pattern or a fine uneven signal pattern (a). The recording pattern is developed to expose the surface of the glass master 10 (b), and the non-developed surface is used as a mask to perform reactive ion etching (RIE) to a desired depth to form guide grooves or minute irregularities on the surface of the glass master 10. (C). Step (d) of manufacturing a glass master 20 by removing the residual photomask. Step (e) of forming a conductive film 13 on the surface of the glass master 20. A metal stamper 1 is formed by plating a metal on the conductive film 13.
Step (f) of fabricating No. 5. Step (g) of peeling the metal stamper 15 from the glass master 20. Finally, the remaining resist is removed by oxygen plasma, a solvent, or the like to complete the stamper 21.

That is, the present invention is characterized in that guide grooves or minute irregularities are formed on the surface of the glass master disk 10 by reactive ion etching (RIE).

Reactive ion etching is an etching method using both ions (ion etching) and active radicals (plasma etching) and has the following characteristics. Anisotropic etching can be performed. Therefore, processing of a fine pattern is possible. The etching rate of the substance to be etched is high, and the selectivity with respect to the photoresist, the base, and the like can be increased. A which was difficult to etch by plasma etching
A sufficiently high etching rate can be obtained also for 1, SiO _{3 and the} like. Therefore, by using such reactive ion etching, the surface of the glass master 10 can be etched very sharply as compared with a polymer such as a photoresist, and the surface roughness of the wall surface is lower than that of the photoresist pattern. Further, it is easy to control the wall angle of the groove, and a groove having a large wall angle can be formed. The etching depth of the glass master 10 by the reactive ion etching is 100 nm or more. As the glass master 10, quartz (including synthetic quartz) is used.

The stamper 21 manufactured as described above
The optical disk substrate 17 having a concave recording signal is copied by an injection molding method (h) using a synthetic resin 16 such as polycarbonate or the 2P method using an ultraviolet curable resin (i), and the recording signal surface thereof is used. An optical disk is completed when a metal reflective film such as aluminum or a magnetic film is formed thereon.

As described above, in the stamper 21 manufactured by the manufacturing method according to the present invention, a groove having a low wall surface roughness and a large wall angle can be formed. When the reproduced optical disk is reproduced by the magneto-optical head, the groove wall surface is difficult to see, and noise due to the surface roughness of the wall surface can be reduced.

[0020]

[Example] Outer diameter 185 mm, inner diameter 20 mm, thickness 6 mm
Then, a synthetic quartz master polished to a surface roughness of 5 nm or less and mirror-polished is prepared, and the master is immersed in a liquid obtained by mixing concentrated sulfuric acid and hydrogen peroxide at a volume ratio of 4: 1 (liquid temperature is 40 ° C.). After immersion for 5 minutes in ultrapure water, alternative Freon (K22 manufactured by Asahi Glass Co., Ltd.)
5ES).

Next, a primer (anchor coat manufactured by Transyl) is spin-coated on the surface of the synthetic quartz master, and then dissolved in propylene glycol monomethyl ether acetate using a positive resist (AZP1350 manufactured by Hoechst) as a solvent to prepare a resist solution. Adjusted and spin coated. Next, using a cutting machine equipped with an Ar ion laser, a radius of 30 mm to
The area up to 0 mm was exposed. The track pitch was 1.0 μm, and continuous exposure was performed with a laser power such that a land (or groove) having a width of 0.5 μm was formed after development. The rotation speed of the synthetic quartz master during exposure was 9
At 00 rpm, the spot diameter of the laser beam is about 0.8 μm.

Thereafter, an inorganic alkali solution (A Hoechst A)
Z developer) and ultrapure water were mixed at a volume ratio of 3: 5 and spin-developed with a diluted developer. The developing conditions at this time are: a pre-pure water application time of 54 seconds, a developer application time of 98 seconds, a post-pure water shower time of 90 seconds, and a spin drying time of 90 seconds. Next, it was post-baked in a clean oven at 120 ° C. for 30 minutes.

Thereafter, the synthetic quartz master was placed in a chamber of a reactive ion etching apparatus (DEA 506 manufactured by Nidec Anelva), and evacuated to a degree of vacuum of 1 × 10 ⁻⁴ Pa.
HF ₃ gas was introduced to perform reactive ion etching. At this time, the gas flow rate was 6 sccm, the gas pressure was 0.3 Pa, the RF power was 300 W, the self-bias voltage was -300 V, the distance between the electrodes was 100 mm, and the etching time was set at 3, 6, and 9 minutes.

Next, concentrated sulfuric acid and aqueous hydrogen peroxide are mixed in a volume ratio of 4:
The synthetic quartz master was immersed in a solution mixed at a ratio of 1 to remove the residual resist. The liquid temperature at this time is 100 ° C,
Processing time is 5 minutes. Then, ultrasonic cleaning was performed with ultrapure water and alternative chlorofluorocarbon to produce a quartz master. When the groove depth of the quartz master was measured, the sample having an etching time of 5 to 10 minutes was 150 nm and 300 nm, respectively.
nm and 450 nm. An Ni conductive film having a thickness of 70 nm was formed on the manufactured quartz master by a sputtering method. In addition, it is also possible to use a vacuum evaporation, an electroless plating method, etc. instead of a sputtering method. Using this Ni conductive film as an electrode, Ni was electroformed for 90 minutes, and 0.3
A Ni master having a thickness of mm was produced. Next, after Ni was peeled off from the glass master, the metal plate was backed to form a Ni stamper.

A land and groove pattern plastic substrate having a diameter of 130 mm was copied from the Ni stamper manufactured as described above by injection molding.

Next, silicon nitride (Si
_After a 3N ₄ ) dielectric layer, a TbFeCo magneto-optical recording layer, and a silicon nitride (Si ₃ N ₄ ) protective layer were formed in this order, a hard code was formed on the film surface with an ultraviolet curable resin.

The optical disk manufactured in this manner was a wavelength of 680 nm, an objective lens NA of 0.55, a vignetting coefficient of 1.0, a wavefront aberration of 0.030λ (rms value), a polarization state of linearly polarized light, and a direction of a guide groove. The signal was reproduced by a pickup in a direction parallel to the above, the reflected light amount signal output was input to a spectrum analyzer, and the noise level of an unrecorded portion was measured. The reproducing light power at this time is:
0mW, rotation speed 3500rpm, radial position 60mm
It is.

The relationship between the groove (step) depth and the noise level at this time is shown by a solid line L2 in FIG. Measurement frequency is 5MHz
It is. As shown in FIG. 4, the groove depth was changed from 150 nm to 4 nm.
Even if it was changed over 50 nm, no increase in the noise level was observed at all as compared with the optical disk manufactured using the stamper manufactured by the conventional manufacturing method, and a low-noise optical disk could be obtained.

Comparative Example First, an outer diameter of 185 mm and an inner diameter of 2
A synthetic quartz master polished to 0 mm, 6 mm in thickness and 5 nm or less in surface roughness is mixed for 5 minutes in a liquid mixture of concentrated sulfuric acid and aqueous hydrogen peroxide at a volume ratio of 4: 1 (liquid temperature is 40 ° C.). After immersion, ultrasonic cleaning was performed with ultrapure water and alternative Freon.

Next, a primer is spin-coated on the surface of the synthetic quartz master in the same manner as in the above embodiment, and then dissolved in propylene glycol monomethyl ether acetate using a positive resist as a solvent to prepare a resist solution. did. At this time, the dilution ratio of the solvent and the photoresist was changed to 150 nm, 300 nm, and 450 nm.
A photoresist master having a thickness was obtained.

Next, a region from a radius of 30 mm to a radius of 60 mm of the synthetic quartz master was exposed by a cutting machine equipped with an Ar ion laser. Track pitch is 1.
Exposure was carried out continuously with a laser power such that a land (or groove) having a width of 0.5 μm was formed after development. The rotation speed of the synthetic quartz master during exposure is 900
rpm, the spot diameter of the laser beam is about 0.8 μm.

Thereafter, spin development was performed with a developer obtained by mixing and diluting an inorganic alkali solution and ultrapure water at a volume ratio of 3: 5. The developing conditions at this time are: a pre-pure water application time of 54 seconds, a developer application time of 98 seconds, a post-pure water shower time of 90 seconds, and a spin drying time of 90 seconds. Next, it was post-baked in a clean oven at 120 ° C. for 30 minutes.

An Ni conductive film having a thickness of 70 nm was formed on the produced glass master by a sputtering method. In addition, it is also possible to use a vacuum evaporation, an electroless plating method, etc. instead of a sputtering method. Using this Ni conductive film as an electrode, Ni was electroformed for 90 minutes to produce a 0.3 mm thick Ni master. Next, Ni was peeled off from the glass master and backed by a metal plate to produce a Ni stamper. Using a Ni stamper manufactured as described above, a land and groove pattern plastic substrate having a diameter of 130 mm was duplicated by injection molding.

Next, silicon nitride (S
After forming an i ₃ N ₄ ) dielectric layer, a TbFeCo magneto-optical recording layer, and a silicon nitride (Si ₃ N ₄ ) protective layer in this order, a hard code was formed on the film surface with an ultraviolet curable resin.

The optical disk manufactured in this manner was a wavelength of 680 nm, an objective lens NA of 0.55, a vignetting coefficient of 1.0, a wavefront aberration of 0.030λ (rms value), a polarization state of linearly polarized light, and a direction of a guide groove. The signal was reproduced by a pickup in a direction parallel to the above, the reflected light amount signal output was input to a spectrum analyzer, and the noise level of an unrecorded portion was measured. The reproducing light power at this time is:
0mW, rotation speed 3500rpm, radial position 60mm
It is.

The relationship between the groove (step) depth and the noise level at this time is shown by a broken line L1 in FIG. Measurement frequency is 5MHz
It is. As shown in FIG. 4, when an optical disk was manufactured using a stamper manufactured by a conventional method, the noise level increased by about 6 dB from a groove depth of 200 nm.

[0037]

As described above, in the method of manufacturing a stamper for an optical disk according to the present invention, a light beam is irradiated onto a glass master coated with a photoresist to expose and record a guide groove pattern or a fine uneven signal pattern. And developing the recording pattern to expose the surface of the glass master, and performing reactive ion etching to a desired depth using the non-developed surface as a mask to form guide grooves or minute irregularities on the surface of the glass master. Removing a residual photomask to form a glass master; forming a conductive film on the surface of the glass master; and plating a metal on the conductive film to form a metal stamper. Removing the metal stamper from the glass master.
Even when the thickness is more than 00 nm, the surface roughness of the groove wall surface is low, the control of the wall surface angle of the groove is easy, and a groove having a large wall angle can be formed. Therefore, even in an optical disk duplicated by such a stamper, a groove with a low wall surface roughness and a large wall angle can be formed, and an optical disk with a low noise level can be manufactured.

[Brief description of the drawings]

FIGS. 1A to 1I are views showing steps of a method for manufacturing a stamper according to the present invention.

FIG. 2 is a sectional view of a main part of the optical disc.

3 (a) to 3 (g) are views showing steps of a conventional stamper manufacturing method.

FIG. 4 is a diagram illustrating a relationship between a groove depth of a stamper and a noise level.

[Explanation of symbols]

3 ... light beam, 10 ... glass master, 11 ... photoresist, 12 ... glass master, 13 ... Ni conductive film, 14 ...
Ni electroformed layer, 15 stamper, 16 polycarbonate synthetic resin, 17 optical disk substrate, 20 glass master, 21 stamper.

Claims (3)

[Claims] 1. A step of irradiating a light beam onto a glass master coated with a photoresist to expose and record a guide groove pattern or a minute uneven signal pattern, and developing the recording pattern to expose the surface of the glass master. Forming a guide groove or minute irregularities on the surface of the glass master by reactive ion etching to a desired depth using the non-developed surface as a mask; and manufacturing a glass master by removing the residual photomask. A step of forming a conductive film on the surface of the glass master; a step of plating a metal on the conductive film to form a metal stamper; and a step of peeling the metal stamper from the glass master. Of manufacturing an optical disk stamper. 2. The method for manufacturing a stamper for an optical disk according to claim 1, wherein the glass master is made of quartz. 3. The method of manufacturing a stamper for an optical disk according to claim 1, wherein the etching depth of the glass master is 100 nm or more.