JP2000021031A - Production of master disk of optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a process and to provide a high-density master disk with narrow pitch tracks below a diffraction threshold and micropitches by using a super-high resolution film which is removed together with a photosensitive member in a developing stage and is reversibly changed in transmittance according to light intensity. SOLUTION: A photoresist 2 and a water-soluble barrier layer 3 are laminated on a glass substrate 1 and the super-high resolution film 4, such as semiconductor particulate dispersion film, which is reversibly changed in transmittance with irradiation energy and can be removed together with the photosensitive member in the developing stage, is formed thereon. A transmittance change is induced by exposure with an Ar laser beam 5, by which desired narrow track pitches and micropit patterns are obtd. at the opening smaller than a light spot. The simultaneous removal of the super-high resolution film 4 is made possible in the subsequent developing stage and the need for providing the stage for removing the super-high resolution film is eliminated. A chalcogen- based phase transition material or ZnS, ZnO, etc., are usable as the material of the super-high resolution film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for manufacturing an optical recording medium. More specifically, the present invention relates to a method for manufacturing a master disc in which a guide groove and a pit are formed by exposing a photosensitive material with a laser beam and developing the photosensitive material.

[0002]

2. Description of the Related Art An optical recording medium that reproduces information or records and reproduces information by irradiating a light beam is a storage device having large capacity, high speed access, medium portability, and others. It has been put to practical use for recording various data such as computer data, and its development is expected in the future.

Techniques for increasing the density of such optical recording media include shortening the wavelength of a gas laser for cutting a master, shortening the wavelength of a semiconductor laser as an operating light source, increasing the numerical aperture of an objective lens, and reducing the thickness of an optical disk. , And others are considered.

[0004] The following briefly describes the conventional master disk manufacturing process. First, a photosensitive substance (photoresist or the like) is applied to a glass substrate to form a photosensitive material. The photosensitive material is irradiated with a laser beam modulated in accordance with an information signal or the like by an exposure device to expose the photosensitive material imagewise. Next, the exposed portions are removed by developing the photosensitive material to form pits or grooves, thereby producing a master. A stamper is manufactured from the master, and a disk substrate is molded by injection molding or the like using the stamper.

Here, in order to form guide grooves or fine pits having a narrow track pitch on the master disk, it is necessary to use light having a wavelength in the ultraviolet region and to condense the light with a lens having a high numerical aperture to reduce the light spot. There is. However, shortening the wavelength of the light source,
When the numerical aperture of the lens is increased, the light spot cannot be reduced below the diffraction limit.

For this reason, a light spot below the diffraction limit is realized by forming a region where the transmittance is substantially high (optical aperture) or a region where the transmittance is low (optical mask) in the region irradiated with light. Attempts have been made to introduce a super-resolution technology into a mastering method. As an example, a narrow track pitch, a sharp guide groove or a minute pit is formed by applying a contrast enhancer manufactured by Shin-Etsu Chemical Co., Ltd. Conventionally, materials that have been tried as super-resolution films have been photobleaching materials such as photobleachable compounds and photochromic materials. These materials are
When the state of the chemical bond or the crystal structure changes in a region where the light intensity (irradiation energy density) is large, the absorption spectrum changes and the transmittance increases. In a region where the light intensity (irradiation energy density) is low, the low transmittance (initial transmittance) before light irradiation is maintained. In addition, since the absorption spectrum changes with the change of the atom movement or the bonding state, in order to return to the initial state before light irradiation, it is necessary to irradiate light of a wavelength different from the wavelength whose transmittance has been changed. . For this reason, light is irradiated at the time of exposure, the transmittance of the super-resolution film made of a photobleaching material or the like changes, and the photosensitive material is not exposed even though the super-resolution effect is obtained. Even when the light was irradiated again, the properties such as the absorption spectrum of the super-resolution film itself changed, and the expected super-resolution effect could not be obtained. In order to return the super-resolution film whose state after light irradiation has changed to the state before light irradiation, it is necessary to irradiate light of different wavelengths, and the optical system of the exposure apparatus becomes complicated. Further, when an inorganic material is to be used as the super-resolution film, a step of removing the super-resolution film itself by dry etching or the like is further required, which complicates the master manufacturing process.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to form a high-density master without forming a track having a pitch smaller than the diffraction limit and minute pits, and without adding a step of removing a super-resolution film. A method for manufacturing a master disc that can be manufactured is provided.

[0008]

SUMMARY OF THE INVENTION <Summary of the Invention><Summary> A method of manufacturing a master of an optical recording medium for forming guide grooves and pits on a substrate according to the present invention includes the following steps. It is a feature. (A) a step of forming a photosensitive layer by applying a photosensitive substance on a substrate; and (b) a super-resolution film whose transmittance reversibly changes according to light intensity on the light-irradiated side of the photosensitive layer. (C) exposing a photosensitive material comprising the photosensitive layer and the super-resolution film in an imagewise manner, and (d) developing the exposed photosensitive material.

<Effects> According to the present invention, it is possible to manufacture a high-density master having tracks with a narrow pitch equal to or less than the diffraction limit and minute pits.

[Detailed Description of the Invention] The method for producing a master according to the present invention comprises the following steps. (A) a step of forming a photosensitive layer by applying a photosensitive substance on a substrate; and (b) a super-resolution film whose transmittance reversibly changes according to light intensity on the light-irradiated side of the photosensitive layer. (C) exposing a photosensitive material comprising the photosensitive layer and the super-resolution film in an imagewise manner, and (d) developing the exposed photosensitive material.

The substrate is arbitrarily selected from those commonly used. Generally, it is selected from glass, acrylic resin, and others.

The photosensitive material can also be arbitrarily selected from those commonly used in the production of masters, but it is preferable to select a material having a higher resolution. Preferred photosensitive materials include diazonaphthoquinone-novolak resin-based positive photoresists and chemically amplified photoresists (for example, poly (p-butoxycarbonyloxystyrene)).
Etc.), and others.

The present invention is characterized in that a photosensitive material having a super-resolution film is used. FIG. 1 shows the dependence of the transmittance (T) of such a super-resolution film on the irradiation energy (E). When the super-resolution film is a heat mode material, the horizontal axis in FIG. 1 is replaced by the film temperature. FIG. 1 shows that the transmissivity of the super-resolution film changes sharply with a specific irradiation energy Ep as a threshold value. At an energy lower than Ep, the light transmittance is low, and at an energy exceeding Ep, the light transmissivity is low. High rate. In the super-resolution film according to the present invention, it is necessary that the transmittance changes reversibly occur at the same wavelength. In a material system in which the transmittance T changes reversibly with respect to the irradiation energy E, a semiconductor or a semiconductor fine particle dispersed film can be used as a typical material.

In a semiconductor or semiconductor fine particle dispersed film,
Those which cause the above-described change in transmittance due to the absorption saturation phenomenon are preferable. The absorption saturation phenomenon means that when electrons are excited from a transition source to a transition destination by light irradiation between two levels involved in photoexcitation, when the number of electrons excited to the transition destination increases, the transition from the transition source to the transition destination occurs. Because the transition probability decreases,
This is a phenomenon in which the excitation light is hardly absorbed and the transmittance increases. The levels used are conduction band, valence band, impurity level,
There is no particular limitation on the exciton level and the like. Basically, it is only necessary that the film be optically changed by electron excitation by light irradiation and change in electron density existing in at least two levels involved in the excitation.

The super-resolution film causes the above-mentioned change in transmittance with an appropriate exposure power and forms an optical aperture smaller than the light spot, thereby realizing a super-resolution operation.

When the super-resolution film of the present invention is provided, a region having a high transmittance is formed only in a region where the irradiation energy is equal to or higher than the threshold value Ep by selecting an appropriate irradiation energy for exposure. . Materials that can be used in the present invention other than the semiconductor or semiconductor fine particle dispersed film system include phase change materials in which light transmittance changes before and after phase transition, for example, crystal and amorphous materials whose light transmittance changes. , Chalcogen-based phase change materials GeSbTe, AgInSbT
e. When a super-resolution film utilizing the absorption saturation phenomenon is used, basically, any material having absorption near the wavelength of the exposure light source can be freely selected. For example, ZnS, ZnO, ZnSe, ZnTe, GaN, G
aP, GaS, AlP, AlAs, SiC, CdS, C
dSe, CdTe, CuCl, and the like. In any of the materials, it is necessary that the transmittance changes with the wavelength of the light source and the irradiation energy for exposure is about one.

In the present invention, these super-resolution materials can be applied as a material dissolved or dispersed in a base material. At this time, any material that does not impair the effects of the present invention can be used. However, it is preferable that the material be a material that is removed together with the photosensitive portion in the developing step (d). More preferably, it is made of the same material as the photosensitive portion of the layer. By using the super-resolution film contained in such a material, it is possible to remove the super-resolution film together with the photosensitive portion of the photosensitive layer during the development processing, so that such a new step is not required. Becomes As such a base material, an alkali-soluble or water-soluble organic compound can be used. For example, an oligomer or polymer having a phenolic hydroxyl group or a carboxylic acid residue can be used. More specifically, phenol, o-chlorophenol, m-
A novolak resin obtained by condensing phenols such as chlorophenol, p-chlorophenol, m-cresol, p-cresol, bisphenol A and 4-chloro-3-cresol with formaldehyde, poly (p-vinylphenol) ), Poly (p-isopropenylphenol), poly (m-isopropenylphenol), a copolymer of p-hydroxystyrene and methyl methacrylate, a copolymer of p-hydroxystyrene and methyl acrylate, p- Copolymers of isopropenylphenol and methyl acrylate, copolymers of p-hydroxystyrene and methacrylic acid, polyamic acids and the like can be mentioned.

Step (a) of forming a photosensitive layer
It is also preferable to form a layer of a substance that can be removed in the developing step (d) between the step (b) of forming the super-resolution film and the step (b). By such means, the super-resolution film can be removed during the development processing. Materials that can be used for forming such a layer include the same materials as those that can be removed by the above-described development processing. When such a layer is formed, the super-resolution film does not need to be held on the medium to be removed in the developing step.

The photosensitive material thus formed is
It is subjected to exposure and development steps by any method. A general method can be used for these steps.

Generally, in the exposure step, exposure is performed with a short-wavelength light source or the like in order to form tracks with narrow pitches and minute pits. As a light source, a g-line, an i-line of a high-pressure mercury lamp, an excimer laser such as KrF or ArF is generally used.

The development step is determined according to the photosensitive material used for the photosensitive layer, but is preferably performed by a method capable of simultaneously removing the super-resolution film during development. Generally, development processing with an alkali developing solution is performed, but aqueous development or the like can be performed if necessary.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 2 is a process chart for manufacturing a master according to the present invention. After cleaning, the glass substrate 1 is treated with a silane coupling agent to obtain good adhesion between the surface and the photoresist (a).

A photoresist 2 is applied on a glass substrate 1 by 15
It was applied to a thickness of 0 nm using a spin coater (b).
In this embodiment, a positive photoresist in which naphthoquinonediazide and a novolak resin were dissolved in a solvent was used. As such a resist, for example, Tokyo Ohka Kogyo OFPR-800 or the like can be used.
After applying the photoresist, a baking treatment was performed at 85 ° C. for 30 minutes.

After the baking treatment, a water-soluble barrier layer 3 was applied by spin coating to a thickness of 100 nm (c). For the water-soluble barrier layer, for example, polyvinyl alcohol or BC5 manufactured by Shin-Etsu Chemical Co., Ltd. can be used. Further, an alkali-soluble organic compound dissolved in an organic solvent may be used as the barrier layer.

As the alkali-soluble organic compound, an oligomer or polymer having a phenolic hydroxyl group or a carboxylic acid residue can be used. More specifically, phenol, o-chlorophenol, m-chlorophenol, p
Novolak resin, poly (p-vinylphenol), poly (p-vinylphenol) obtained by condensing phenols such as -chlorophenol, m-cresol, p-cresol, bisphenol A, and 4-chloro-3-cresol with formaldehyde p-isopropenylphenol), poly (m-isopropenylphenol), a copolymer of p-hydroxystyrene and methyl methacrylate,
Examples include a copolymer of p-hydroxystyrene and methyl acrylate, a copolymer of p-isopropenylphenol and methyl acrylate, a copolymer of p-hydroxystyrene and methacrylic acid, and a polyamic acid. Organic solvents include, for example, toluene, xylene, dimethylformamide, dimethylacetamide, methyl cellosolve,
o-dichlorobenzene, chloroform, ethanol, i
-Propyl alcohol, diclopentane, cyclohexane, ethyl cellosolve acetate, acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, and others,
Can be used alone or in the form of a mixture. As the super-resolution film 4, a photoresist made of a previously exposed naphthoquinonediazide and a novolak resin and a sol-gel method (for example, Guangming Li et al., J. Appl. Phys. 75 427)
6 (1994)) was applied to a thickness of 300 nm using a spin coater. After applying the super-resolution film, baking treatment was performed at 85 ° C. for 60 minutes. The super-resolution film 4 is made of ZnSe (with an energy gap of 2.7 eV).
Is a ZnSe semiconductor fine particle dispersion film dispersed in the material of the photosensitive portion of the resist. The ZnSe volume ratio and the particle size are adjusted to adjust the band gap to about 3.5 eV.

Using this as a light source, a Kr ion laser (wavelength 3
The guide groove having a track pitch of 0.2 to 1.0 μm and a pit width of 0.1 μm were obtained by an exposure apparatus having an NA of 0.9 and a NA of 0.9.
A pit pattern of 2 to 1.0 μm was exposed (e).

After the exposure, development was performed using an inorganic alkali developer (f). By making the structure of the super-resolution film a semiconductor dispersed in a pre-exposed photoresist,
It was confirmed that the super-resolution film could be removed only by using the inorganic alkali developer as in the conventional case.

Also, as a conventional example, a master was prepared in the case where no super-resolution film was provided.

A stamper was manufactured from the two types of masters thus obtained and the conventional example by electroforming in the same manner as in the prior art. Using this stamper, injection molding was performed by an injection device to produce a disk substrate. The cross-sectional structure of the manufactured disk substrate was observed using an atomic force microscope (AFM). In addition, Al was formed on the disk substrate by a magnetron sputtering apparatus, and the width of each pit was reproduced to measure the signal intensity. The light source of the reproducing apparatus has a wavelength of 413.
nm Kr gas laser, NA 0.6.

From the results of AFM observation, it was found that a good guide groove could not be obtained with a track pitch of 0.5 μm or less for the disk substrate manufactured from the conventional master, but the disk base manufactured from the master according to the present embodiment was not used for the track. Pitch 0.3μm
A good guide groove was confirmed. FIG. 3 shows the measurement result of the reproduction signal intensity. In the conventional example, a high CNR of 50 dB or more is obtained up to a pit width of 0.6 μm.
Below 5 μm, CNR decreases. On the other hand, in the present example, a CNR of 50 dB or more was obtained up to 0.3 μm.

Example 2 A master was produced in the same manner as in Example 1 except that a super-resolution film in which ZnO was dispersed in SiO ₂ was used, and a disk substrate was produced. After coating the barrier layer, the glass substrate was mounted on a substrate holder of a magnetron sputtering apparatus, and a ZnO (fine particle dispersion film) in which ZnO (energy gap 3.2 eV) was dispersed in SiO ₂ as a super-resolution film 4 was formed by sputtering. A film was formed with a thickness of 100 nm. The ZnO fine particle dispersed film is adjusted so that the band gap becomes 350 nm by adjusting the volume ratio and the particle size. When the same evaluation as in Example 1 was performed, the effects of the present invention could be obtained.

Embodiment 3 In this embodiment, a ZnSe mixture of naphthoquinonediazide and a novolak resin was used as the super-resolution film in the same manner as in Embodiment 1.
A master was prepared using a semiconductor fine particle dispersion film in which was dispersed. Further, as a conventional example, a master was manufactured using a photobleaching material (for example, a contrast enhancement layer manufactured by Shin-Etsu Chemical Co., Ltd. can be used) for the super-resolution film. In both the present example and the conventional example, exposure was performed so as to form a 0.4 μm guide groove and a 0.2 μm pit.
A stamper was produced from the two types of masters obtained in this manner and the comparative example by electroforming in the same manner as in the conventional method. Using this stamper, injection molding was performed by an injection device to produce a disk substrate. If the size of the pits to be formed is as small as 0.2 μm, it is difficult to form sharp pits even with a super-resolution film. When both disks were observed by AFM, pits very small than 0.2 .mu.m and missing portions were found to the same extent. The super-resolution film used in the present embodiment is a semiconductor fine particle dispersed film, which changes the transmittance by absorption saturation, so that the bonding state of the conventional chemical bond changes and the transmittance changes. Unlike super-resolution films, they can be used repeatedly at a single wavelength. Therefore, when forming a 0.2-μm pit, exposure was performed five times in duplicate, a master was prepared, and a disk was prepared in the same manner. When this disk was observed by AFM, it was confirmed that the pits were not missing and the pits had a shape of almost 0.2 μm. That is, by performing overlapping exposure, minute pits can be accurately formed without missing.

[0034]

According to the present invention, it is possible to manufacture a high-density master having narrow tracks and narrow pits having a pitch equal to or less than the diffraction limit, as described in the section of the Summary of the Invention. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between irradiation energy and transmittance of a super-resolution film.

FIG. 2 is a process chart showing an example of a master production method according to the present invention.

FIG. 3 is a diagram illustrating a relationship between a pit width and a CNR according to the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Photoresist 3 Barrier layer 4 Super-resolution film 5 Ar ion laser beam 6 Photosensitive part

Claims (5)

[Claims] 1. A method of manufacturing a master of an optical recording medium, comprising forming a guide groove and a pit on a substrate, comprising the following steps. (A) a step of forming a photosensitive layer by applying a photosensitive substance on a substrate; and (b) a super-resolution film whose transmittance reversibly changes according to light intensity on the light-irradiated side of the photosensitive layer. (C) exposing a photosensitive material comprising the photosensitive layer and the super-resolution film in an imagewise manner, and (d) developing the exposed photosensitive material. 2. The method according to claim 1, wherein the super-resolution film is made of a material which is removed together with the photosensitive portion in the developing step (d). 3. A step of forming a layer of a substance that can be removed in the developing step (d) between the step (a) of forming a photosensitive layer and the step (b) of forming a super-resolution film. 3. The method of manufacturing a master according to claim 1, further comprising: 4. The method for producing a master according to claim 1, wherein the super-resolution film is a film in which semiconductor fine particles are dispersed. 5. Between the exposure step (c) and the development step (d), exposure is performed again with an exposure pattern different from the exposure pattern in the initial exposure step (c), thereby producing a master for the subsequent exposure pattern. A method for producing a master according to any one of claims 1 to 4.