JPH04298833A - Production of master disk for optical disk - Google Patents

Abstract

PURPOSE:To increase the recording density of an optical disk and to obtain good signal characteristics by executing a surface hardly solubilizing treatment between an exposing stage and a developing stage and flattening land parts to lower a signal to noise ratio. CONSTITUTION:The surface of a photoresist film is made hardly soluble if the master disk is produced by adding the hardly solubilizing treatment (short- time contact processing by a dilute developer, etc.), rinsing and drying stages before development and, therefore, the threshold value of the development appears to increase up to position shown by a dotted line (a) in spite of development afterward and the pit section is like (a) under developing conditions after exposing at the same exposure. The sensitivity of the photoresist is as if the sensitivity is lowered and, therefore, the depth and width of the grooves and pits decrease. Since the exposure in a transverse direction is small, as commpared with the exposure in a depth direction, the pit width decreases even if the exposure and developing conditions are so changed as to attain the same depth. Then, the grooves and pits having the small width and diameter are thus formed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a master disc for an optical disc. More specifically, the present invention relates to a method for producing an optical disk master that allows controlling the groove width and pit size of the master without changing the exposure mastering device.

0002

[Prior Art] Conventionally, master discs for optical discs are made by coating a glass disc as a base with a positive photoresist film, heating and drying it, and then using a laser beam to create concentric or spiral grooves or pit patterns. It is manufactured by exposing to light to form a latent image, developing this, and then performing steps such as washing with water and drying.

0003

[Problems to be Solved by the Invention] According to the conventional optical disk master manufacturing method, the intensity distribution of the exposure beam has a Gaussian distribution, so that the latent image formed by exposure on the photoresist film also has approximately It becomes a Gaussian distribution. The exposure beam diameter is approximately λ/NA, where NA is the numerical aperture of the focusing lens and λ is the wavelength of the light. The pit cross section formed by development changes from a to e as development progresses, as shown in FIG. 1, since the latent image has a substantially Gaussian distribution including halftone areas. In the figure, 1 is a substrate, and 2 is a photoresist film. In order to obtain a large number of reproduced signals from the pits when used as an optical disc, it is preferable that the pit depth be in the range of λD /3n to λD /6n, where λD is the wavelength of the light used during reproduction. Here, n is the refractive index of the optical disc substrate. Considering process stability, conventionally the photoresist film thickness was set to λD /3n ~ λD, which is the same as the depth of the pit.
/6n. In order to ensure a sufficient level of the reproduced signal, the area with the above-mentioned depth is required to be 1/2 to 1/3 of the spot diameter of the reproduced light.

[0004] In order to increase the recording density of an optical disk, it is necessary to narrow the interval between recording tracks and the interval between data in the track direction. Must. exposure beam λ
It is possible to reduce /NA, but since NA (NA < 1) is already used in normal equipment exceeding 0.9, the range of improvement is small, and therefore the wavelength λ of light must be reduced. It won't happen. However, as a light source for producing an optical disk master, a transverse single mode laser capable of continuous oscillation and sufficiently narrowing down is required, and there is no laser with a wavelength λ smaller than the near-ultraviolet region. Even for light with wavelengths in the near-ultraviolet range, lenses with large NAs that can be used in the air will have to wait for future development, and maintenance and adjustment of exposure mastering machines will also be difficult because visible light is not available. There is. Therefore, a method other than reducing the exposure beam diameter becomes necessary.

Furthermore, regarding the reproduced signal from the groove, in order to obtain optimal signal characteristics, it is necessary to set the groove depth and groove width to predetermined values. Normally, when changing the relationship between the two, it is necessary to change the NA of the objective lens as described above or to change the wavelength of the laser. Furthermore, for this purpose, a method is used in which the diameter of the laser beam incident on the objective lens is adjusted using an aperture or a set of expander lenses. These adjustments are extremely difficult. Furthermore, for the above reasons, the relationship between groove depth and width cannot be changed independently with the same optical system, making it extremely difficult to adjust the optical system to obtain a predetermined groove depth and groove width. It is. An object of the present invention is to produce an optical disk master having good signal characteristics by controlling the groove width and the pit width and diameter without changing the exposure mastering machine.

[0006]

[Means for Solving the Problems] The above object is achieved by subjecting the surface of a photoresist film to a specific treatment. Great effect can be obtained. The gist of the present invention is a method of forming a photoresist film on a glass substrate, exposing the photoresist film to a desired pattern with a light beam, and then developing the photoresist film to produce an optical disc master. The present invention resides in a method for producing an optical disc master, characterized in that a surface treatment to make the surface difficult to solubilize is performed between the above-mentioned exposure step and development step.

That is, by exposing a photoresist to a predetermined pattern and then making the entire surface of the photoresist somewhat insoluble, the rise of the developed pattern near the surface of the photoresist as shown in FIG. 1 is made to have an acute angle. It is something. To make it less soluble, photoresist has the property that when it comes in contact with a developer and then washed with water, the surface hardens and becomes less soluble, so you can use this, or you can irradiate the entire surface of the photoresist with weak light for a short period of time. Although the following methods are possible, a method of processing with a developer or a diluted developer is preferable.

The principle is shown in FIGS. 2 and 3. FIG. 2 shows the exposure beam intensity distribution, where I is the intensity and r is the distance from the beam center. FIG. 3 shows a cross section of the developed photoresist pattern. D is the depth. If the conventional method of manufacturing an optical disc master is used, the pit cross section will be as shown in A. If a master is prepared by adding a treatment to make it insoluble (short-time contact treatment with a diluted developer, etc.), washing with water, and drying before development, the surface of the photoresist film will be made to be insoluble, so it will not be possible to develop it later. Also, the threshold value for development appears to have risen to the position shown by the dotted line in FIG. 3, and the pit cross section becomes as shown in FIG. It is as if the sensitivity of the photoresist has decreased, so the depth and width of the grooves and pits become shallower and narrower. Since the amount of exposure in the lateral direction is smaller than that in the depth direction, even if the exposure amount and development conditions are changed to maintain the same depth, the pit width will be narrower. Therefore, it becomes possible to create grooves and pits with small widths and diameters.

Furthermore, by appropriately changing the concentration and time of the developer used to make the photoresist less soluble before main development, the relationship between the width and depth of grooves and pits can be adjusted without adjusting the optical axis system. It can be changed. Usually, the base is a flat glass disk. The glass disc is cleaned and
It is also preferable that a coupling layer is provided on the surface to improve adhesion with the photoresist film. Next, a positive photoresist film is applied to the surface and dried with heat. The appropriate thickness of the photoresist after drying is 0.1 to 0.2 μm. This is then processed by an exposure mastering machine.
Expose a pattern of grooves and pits. That is, a laser beam is focused onto the photoresist film using a lens,
A latent image of the pattern is formed on a photoresist film. Next, the photoresist surface is treated to make it less soluble. The insolubility treatment is usually carried out by applying a developer or a diluted developer to the photoresist surface and washing it with water. In this way, a poorly soluble layer is created on the surface of the photoresist.The thickness of this poorly soluble layer varies depending on the concentration of the developer applied to the surface and the time taken.Developing, rinsing, and drying with the hardly soluble layer present As described above, a pattern with a small width and diameter can be obtained. When applying a diluted developer or developing solution during the treatment to make it difficult to dissolve, it may be applied directly if an extremely diluted solution is used, but if a thicker solution is used, water contact may be applied as a pre-process to improve wettability. Preferably, the treatment is carried out.

0010

[Examples] The present invention will be explained in more detail using Examples below, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. Example 1 The surface of a glass substrate was polished and cleaned, and a silicon-based coupling agent was applied and dried to form an extremely thin (single-molecule to several-molecule layer) layer. Next, a resist solution prepared by diluting a novolac resin-based positive photoresist (MCPR manufactured by Mitsubishi Kasei Corporation) with ethyl cellosolve acetate at a ratio of 35% by weight was spin-coated, and the resist solution was heated at 100°C for 30 minutes using an electric oven.
Dry for 0 minutes. The resulting resist film had a thickness of 1600 Å. The master disk obtained in this way has a NA of 0.93.
, λ=459nm, power=3μm, linear velocity=5.6m
/sec exposure mastering machine,
This is a developed image. As a pretreatment before main development, NaOH
Using a developer with a concentration of 0.02N, the development time was 5.
seconds or 10 seconds. If the concentration of the developer is too high, the amount of surface etching of the photoresist film will increase and the surface will become rough; if it is too low, the effect of forming a hardened layer will be small. The extent of this is shown in Figure 4. (0 seconds in the figure is the case where no pretreatment was performed.) After pretreatment and development to make it difficult to dissolve, be sure to wash with water. The formation effect is small. The concentration of the developer is N
aOH concentration is 0.01N to 0.20N, time is 5 to
In the range of 60 seconds, surface roughness is small and the effect of forming a hardened layer is large. From Figure 4, the depth becomes shallower for the same amount of exposure, so it is necessary to increase the amount of exposure to achieve the same depth, but the amount of exposure is less than twice that of the normal case, and The burden of the laser is small. When the groove depth is 0.1 μm, 5 seconds of pre-development results in a reduction of approximately 5%, and 10 seconds of pre-development results in a reduction of approximately 1%.
A groove width that is 0% narrower is obtained. In this way, by changing the pre-development time, the relationship between groove width and groove depth can be adjusted without greatly changing the optical system of the mastering machine or the exposure conditions.

[0011]

[Operation] When the distance between the track grooves becomes smaller, about 1 μm, in the conventional method, the base portions of the exposure beam distribution overlap between adjacent tracks, so that the intermediate portion between the grooves also overlaps.
It gets etched during development and the flat part disappears. On the other hand, according to the present invention, since a hardly soluble layer is formed on the surface, a flat portion remains. For example, when recording pits for data signals in the land area between grooves as in a magneto-optical disk, with the conventional method, as the groove spacing is narrowed, noise due to surface irregularities not only increases. , the surface is not flat, resulting in a reduced signal-to-noise ratio. According to the present invention, since the land portion is flat, even if the groove spacing is narrowed, the signal-to-noise ratio will not deteriorate much, so it is expected that the density of the optical disc will be increased. Furthermore, if the present invention is used in combination with a means for reducing the size of the exposure beam system for producing the master disc, for example, a means for shortening the exposure beam wavelength, it is possible to form even more grooves.
If used in combination with means for reducing the pit width and diameter, it becomes possible to further reduce the groove and pit width and diameter.

0012

According to the present invention, in the development process after pattern exposure for forming grooves and pits in the photoresist film, the process of washing with water and pretreatment development is performed before the conventional development process. By adding this to the manufacturing process of optical disc masters, it becomes possible to create master discs having grooves and pits with small widths and diameters. Furthermore, by changing the pre-development time and density, it is possible to produce a master disc with good signal characteristics. The above-mentioned additional steps can be realized using conventional master production equipment without adding new special equipment, and the time required for the steps is short. In addition, the optical disc master produced by the present invention can be treated in the same way as an optical disc master produced by the conventional method, and this master can be used to produce a metal stamper by electroforming or by photo-curing. Plastic stampers can be made using resin, and it is possible to make large quantities of replica disks from these stampers.

[Brief explanation of drawings]

[Figure 1] Cross-sectional view showing a cross section of a pattern formed by development

[Figure 2] Explanatory diagram showing exposure beam intensity distribution

[Figure 3] Explanatory diagram showing a cross section of a developed pattern

[Figure 4] Diagram showing the measurement results of the width and depth of the grooves on the master disk of the example

[Explanation of symbols]

1　　　　Substrate 2 Photoresist film

Claims (3)

[Claims] 1. A method for producing an optical disk master by forming a photoresist film on a glass substrate, exposing the photoresist film to a light beam to form a desired pattern, and then developing the photoresist film, comprising: 1. A method for producing a master for an optical disc, comprising performing a surface refractory treatment between an exposure step and a development step. 2. The manufacturing method according to claim 1, wherein the surface refractory treatment comprises a step of bringing a diluted developer or a developing solution into contact with the surface of the photoresist and a water washing step. [Claim 3] The surface refractory treatment consists of a step of bringing water into contact with the surface of the photoresist to improve wettability, a step of bringing a diluted developer or developer into contact with the surface of the photoresist, and a water washing step. The manufacturing method according to claim 1, characterized in that: