JPH04335230A - How to make an optical disc master - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 forming grooves and pits with small pattern sizes.

0002

[Prior Art] Conventionally, an optical disk master disc (a) in FIG.
) to (d), after applying a positive photoresist film 2 to a glass disc 1 serving as a substrate and heat-treating it, a laser beam 3 is focused by a lens 4 and irradiated onto the photoresist film 2, forming a concentric or A latent image 5 is formed by exposing a spiral pregroove or pit pattern, and this is developed to form an uneven pattern 6 corresponding to the pregroove or pit on the photoresist film 2, and further heat treatment is applied. Manufactured by.

FIG. 6 schematically shows a conventional optical disk master recording device. The recording optical system of this device splits a laser beam emitted from an Ar laser 8 into a pregroup beam and a pit beam by a mirror 9, and sends each laser beam to analog modulators 10 and 11 and a digital modulator 12, respectively.
, 13 and magnifying lens systems 14 and 15, are combined by a beam splitter 16, guided to an objective lens 17, and irradiated onto a master 18. In FIG. 5, the master 18 is a glass disk 1 coated with a positive photoresist film 2. As shown in FIG. In addition, a focusing optical system for following the surface wobbling of the master 18 when it rotates guides the beam emitted from the He-Ne laser 19 to the objective lens 17 to irradiate the master 18, and sends the reflected light from the master 18 to the beam splitter. 20 makes the light incident on the detector 23, and the control circuit 22 drives the actuator 23 based on the incident signal from the detector 21, and the actuator 23 drives the objective lens 17. In the figure, 24 is a motor that rotationally drives the master 18, 25a and 25b are quarter-wave plates, 26a to 26c are mirrors, 27a and 27b are dichroic mirrors, and 28
is a cylindrical lens.

0004

By the way, in order to increase the recording density of an optical disc, it is necessary to narrow the recording track spacing and the data spacing in the track direction. diameter must be reduced. To achieve this, the ratio λ/N of the exposure beam diameter λ and the numerical aperture NA of the objective lens is required when recording information on the master disc.
You can make A smaller, but the theoretical limit value of numerical aperture NA is 1.
, and since those with NA exceeding 0.9 are already in use, the scope for improvement is small. Therefore, it is common practice to shorten the wavelength λ of light. However, if the wavelength λ of the exposure beam is simply shortened, the light intensity will be insufficient, so it is necessary to adopt a wavelength λ with high resist sensitivity to achieve matching. For this reason, as a general laser light source for cutting,
Helium cadmium (He-c) with a wavelength of 441.6 nm
d) Laser or Argon (Ar) with a wavelength of 457.9 nm
) uses a laser. However, with laser light of these wavelengths, the resist spectral sensitivity of the positive photoresist film increases, and a photoreaction occurs even at low light intensity, causing shoulder sagging in the groove cross-sectional shape of the pre-pits and pre-grooves where information is recorded. In the end, the data interval was not narrowed.

[0005] As another method for increasing the recording density of an optical disk, a manufacturing method that adds a developing step, washing, and drying has been proposed, as shown in Japanese Patent Laid-Open No. 1-317241. This method involves immersing an unexposed photoresist film in a developer solution as a pre-process of exposing the recesses of pre-grooves and pre-pits to the photoresist film.
Alternatively, the film may be showered with a developer and then washed with water and dried. However, this method has a problem in that the information recording master disc may have many defects.

The present invention has been made in view of such conventional problems, and provides an optical disc master that makes it possible to increase the information recording density by reducing shoulder fluctuations in the groove cross-sectional shapes of pre-grooves and pre-pits. The purpose of this invention is to provide a method for manufacturing.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention forms prepits corresponding to tracking pregrooves and address pits by irradiating a laser beam onto a positive photoresist photosensitive layer provided on a substrate. In the method for manufacturing an optical disk master in which recesses are formed, the wavelength of the laser beam is adjusted to such a level that the absorbance of the positive photoresist is 0.1.
It is characterized by having a wavelength in the following range.

[0008] Furthermore, in order to achieve the above object, the present invention has the following features:
The wavelength of the laser beam may be in the range of 465 nm or more and 529 nm or less.

The principle of the method for manufacturing an optical disk master according to the present invention will be explained with reference to FIGS. 3 and 4. FIG. 3 is a graph showing the relationship between the absorbance of a positive photoresist and exposure wavelength, and FIG. 4 is a graph showing the relationship between wavelength and light intensity. As can be seen from these figures, when comparing the absorbance at a wavelength of 457.9 nm and a wavelength of 488 nm, the degree of increase in light intensity of the Ar laser at a wavelength of 488 nm is greater than the degree of decrease in resist sensitivity. That is, as the wavelength becomes shorter, the absorbance increases, and as the wavelength becomes longer, the absorbance decreases, but the light intensity output is greater than the decrease in the absorbance, and there is no shortage of light intensity. Such a wavelength range is a range where the absorbance is 0.1 or less, that is, a wavelength range of 465 nm or more and 529 nm or less. Further, when such a long wavelength range is used for exposing a positive photoresist, a photoreaction will not occur unless a high amount of light is applied. The method for producing an optical disc master according to the present invention utilizes these.

0010

Embodiment Next, an embodiment of the present invention will be described in comparison with a conventional example with reference to FIG. FIG. 1 shows the relationship between light intensity and the cross-sectional shape of the resist layer, with the upper part of the figure showing the intensity distribution of the exposure laser beam, and the lower part showing the cross-sectional shape of the grooves of the pre-pits in the developed photoresist. In the figure, A is the light intensity distribution of the laser beam in the conventionally used wavelength range, and B is the light intensity distribution of the laser beam in the wavelength range used in the present invention. Further, in the figure, C shows the conventional groove cross-sectional shape, and D shows the groove cross-sectional shape according to the present invention.

[0011] For the optical disc master, a glass disc serving as a substrate is coated with a positive type photoresist of Shipley Co., Ltd. S1400 at 0.00.
After coating to a thickness of 26 μm and heat-treating, the photoresist film was irradiated with a recording beam to form recesses for forming pre-grooves and pre-pits. The recording device is the same as the device shown in Fig. 6, and the numerical aperture of the objective lens is set to NA=0.91.
The recording wavelength of the conventional example is 457.9 nm, and the recording wavelength of the embodiment of the present invention is 488 nm, and the light intensity is four times that of the conventional example. When exposed at a wavelength for which the photoresist layer X has low sensitivity, the photoresist layer X reacts only in areas where a large amount of light is obtained, and the intensity distribution in the high light amount region (above the broken line H in the figure) where the photoresist layer X reacts. Since is steep, the groove cross section is steep, and groove shape D with less shoulder sag is obtained. On the other hand, in the wavelength range conventionally used, the resist spectral sensitivity of the resist is high and a photoreaction occurs even at low light intensity.
Shoulder sagging occurs in the groove cross-sectional shape C of the pre-pits and pre-grooves in which information is recorded. FIG. 2 shows shapes corresponding to cross-sectional electron microscope (SEM) photographic images of pre-pits and pre-grooves produced according to the embodiment of the present invention and the conventional example.

[0012] The size of the shape of the pre-pits and pre-grooves can be varied by varying the light intensity. Furthermore, when the photoresist layers have different thicknesses, the light intensity may be varied to obtain an appropriate groove shape. Furthermore, the wavelength can be selected by simply moving a wavelength selection prism at the rear end of the Ar laser, for example, and can be realized using conventional master production equipment without adding new special equipment.

[0013]

[Effects of the Invention] As explained above, the method for producing an optical disc master according to the present invention is for forming pre-pits corresponding to tracking pre-grooves and address pits by irradiating a photosensitive layer of positive photoresist provided on a substrate. The wavelength of the laser light used to form the recesses was set to a wavelength in which the absorbance of the positive photoresist is 0.1 or less, so shoulder sagging is small and pre-pits and pre-grooves with smaller groove width and groove diameter than before can be created. This has the effect of making it possible to form optical discs with higher density. In addition, since there is no need to change the conventional master disc production process, it can be handled in the same way as before, and there is an effect that an information recording master disc with low defects can be produced.

[Brief explanation of drawings]

FIG. 1 shows the relationship between light intensity and cross-sectional shape of a resist layer in an embodiment of the present invention and a conventional example, with the upper part of the figure showing the intensity distribution of the exposure laser beam and the lower part showing the developed and 3 is a graph showing the groove cross-sectional shape of pre-pits in a photoresist.

[Fig. 2] Fig. 2 shows a cross-sectional electron microscope (S
EM) A cross-sectional view showing the groove shape corresponding to the photographic image.

FIG. 3 is a graph showing the relationship between the absorbance of a positive photoresist and the exposure wavelength.

FIG. 4 is a graph showing the relationship between wavelength and light intensity.

FIG. 5 is a cross-sectional view showing a procedure for manufacturing an optical disc master.

FIG. 6 is a block diagram schematically showing an optical disc master recording device.

[Explanation of symbols]

A. Light intensity distribution of the laser beam in the wavelength range used in the conventional example B. Light intensity distribution of the laser beam in the wavelength range used in the embodiment of the present invention C. Groove cross-sectional shape formed in the conventional example D. Groove cross-sectional shape X Photoresist layer

Claims (2)

[Claims] 1. A method for producing an optical disc master in which a photosensitive layer of positive photoresist provided on a substrate is irradiated with laser light to form recesses for forming pre-pits corresponding to tracking pre-grooves and address pits, the method comprising: The absorbance of positive photoresist is 0 for the wavelength of light.
．． A method for producing an optical disc master, characterized in that the wavelength is in the range of 1 or less. 2. The method for producing an optical disk master according to claim 1, wherein the wavelength of the laser beam is set to 465 nm or more and 529 nm or less.