JPH07287874A - Production of optical master disk - Google Patents

Abstract

PURPOSE:To improve a recording density by providing the surface of a resist layer with a transmitted light limiting layer contg. a material to allow transmission of only the light having the intensity higher than the prescribed intensity, exposing this resist layer via this layer and enabling formation of extremely small phase pits beyond the limitation by lambda/NA. CONSTITUTION:The resist layer 2 is first formed on a transparent glass substrate 1 by applying a photoresist thereon by a spin coating method, etc., in order to produce an optical master disk. Saturable dyestuff is likewise applied by a spin coating method, etc., on the layer 2, by which the transmitted light limitation layer 3 is formed. The substrate 1 provided with these layers 2, 3 is exposed by using an optical recorder (cutting machine) using a laser beam 11. Namely, the laser beam L emitted from a laser beam source 11 is reflected by a mirror 12 and is made incident on an electro-optic modulator 13. The laser beam L modulated in the intensity is reflected by mirrors 15, 16 and is converged by passing an objective lens 14, by which a spot is generated on the layer 2. The substrate 1 is rotated and the lens 14 and the mirror 16 are moved in the diametral direction of the substrate 1 by a moving mechanism, by which the phase pits are concentrically or spirally 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 manufacturing an optical disk master (so-called mastering process) for forming phase pits according to an information signal.

[0002]

2. Description of the Related Art For optical discs such as digital audio discs (so-called compact discs) and video discs, an aluminum reflective film is formed on a transparent substrate in which phase pits are formed in advance in accordance with an information signal, and a protective film is formed thereon. It is configured by forming a film or the like.

The formation of the phase pits is generally carried out by a so-called mastering process in which a photoresist coated on a glass substrate is exposed by laser to produce an optical disc master.

The laser light focused on the resist layer by the objective lens has a concentric intensity distribution, and its spot diameter is λ / NA (where λ is the wavelength of the laser light and NA is the objective). It is the numerical aperture of the lens.)
Proportional to.

On the other hand, in the mastering process, the size of the phase pits formed on the resist layer by exposure is limited by the spot diameter. That is, the smaller the spot diameter of the laser light with which the resist layer is irradiated, the smaller the phase pits can be formed.

Therefore, a conventionally known method is to cope with this by shortening the wavelength λ of the laser light used for exposure or increasing the numerical aperture NA of the objective lens.

[0007]

However, the numerical aperture NA of the objective lens has already been set to a large value close to the limit. Regarding the wavelength λ of the laser light, blue laser light with a short wavelength has already been used, and in order to perform higher density mastering,
Furthermore, although there is no choice but to use laser light of a shorter wavelength, for example, laser light in the ultraviolet region, it is difficult to dramatically improve the recording density even if laser light in the ultraviolet region is used.

As described above, in the mastering process of the optical disc, the size of the phase pit is actually limited by λ / NA. Therefore, the present invention has been proposed in view of such conventional circumstances, and provides a method for manufacturing an optical disc master capable of forming dramatically small phase pits exceeding the limit of λ / NA. With the goal.

[0009]

In order to achieve the above-mentioned object, a method of manufacturing an optical disk master according to the present invention comprises forming a resist layer on a substrate and selectively exposing the resist layer according to an information signal. When forming a phase pit by development, a transmitted light limiting layer containing a substance that transmits only light having a predetermined intensity or more is provided on the resist layer, and the resist layer is exposed through the transmitted light limiting layer. It is characterized by.

In the present invention, the material used for the transmitted light limiting layer may be any substance as long as it transmits only light having a predetermined intensity or higher, and examples thereof include saturable dyes.

The saturable dye has a characteristic that it hardly transmits low-intensity light and only transmits light of a certain level or more due to an absorption saturation phenomenon upon light irradiation. Specific examples include phthalocyanine dyes, rhodamine dyes, erythrosine dyes, fluorescein dyes, stilbene dyes, and the like, which may be selected according to the wavelength of the laser beam used for exposure.

For example, when a red laser light having a wavelength of about 700 nm is used, a phthalocyanine dye is used, and when a green laser light having a wavelength of about 530 nm is used, a rhodamine dye or erythrosine dye is used at a wavelength of 470 n.
When a blue laser beam near m is used, a fluorescein dye or a stilbene dye can be used, respectively.

[0013]

[Function] When a laser light having a concentric intensity distribution is irradiated to a transmitted light limiting layer containing a substance such as a saturable dye that transmits only light having a predetermined intensity or more, the laser light is emitted at the center of the laser spot. The laser light is transmitted because of its high intensity.

On the other hand, in the peripheral portion of the laser spot, the laser light is absorbed by the transmitted light limiting layer and is not transmitted. As a result, the spot diameter of the laser light that has passed through the transmitted light limiting layer is significantly smaller than the spot diameter of the laser light that has not passed through the transmitted light limiting layer.

Therefore, when the resist layer is irradiated with the laser beam through the transmitted light limiting layer, the resist layer is exposed with a very small spot diameter which is not restricted by λ / NA, which exceeds the limit of λ / NA. Small phase pits are formed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments to which the present invention is applied will be described in detail below with reference to the drawings.

In order to manufacture an optical disk master, first, as shown in FIG. 1, a transparent glass substrate 1 is prepared, and a photoresist is applied on the transparent glass substrate 1 by a method such as a spin coating method to form a resist layer 2. To form. As the photoresist used for the resist layer 2, any photoresist can be used, and normally a positive photoresist is used.

Next, as shown in FIG. 2, a saturable dye is applied onto the resist layer 2 by a method such as spin coating to provide a transmitted light limiting layer 3. It is necessary to select the saturable dye used in the transmitted light limiting layer 3 in accordance with the exposure wavelength. In this example, the porphyrin-based dye (Zn -Tetraphenylporphine) was applied to 300 nm.

[0019]

[Chemical 1]

Thus, the resist layer 2 and the transmitted light limiting layer 3
The glass substrate 1 provided with was exposed using an optical recording device using laser light, a so-called cutting machine.
The cutting machine used has a structure as shown in FIG.

[0021] That is, the cutting machine includes a laser light source 11, a mirror 12 for guiding the laser beam L emitted from the laser light source 11 to the subsequent optical system, according to the recording signal S _W inputted laser light L Electro-optical modulator (EOM) 13 for intensity modulation by means of mirrors, and mirrors 15, 1 for guiding intensity-modulated laser light L to objective lens 14.
6 and an objective lens 14 that irradiates the laser light L with a predetermined spot diameter.

The objective lens 14 and the mirror 16 arranged immediately in front of the objective lens 14 are arranged on a movable member (not shown) so that the objective lens 14 faces the transmitted light limiting layer 3 on the glass substrate 1 with a minute gap, and is known. The movement mechanism allows the glass substrate 1 to be moved in the radial direction. Therefore, by irradiating (exposure) the laser beam L through the objective lens 14 while rotating the glass substrate 1 and developing it, phase pits are formed in the resist layer 2 in a concentric or spiral shape.

The EOM 13 is an optical modulator that utilizes the change in the refractive index of the medium due to the electro-optical effect (a phenomenon in which the refractive index of the medium changes depending on the applied signal electric field, which is also called the Pockels effect). Incident laser light L
(Normally linearly polarized by a Brewster window) is controlled by an electric field to which an optical phase difference between two orthogonal polarization components in a medium is applied, and the polarization state changes. Specifically, the laser light L that has passed through the EOM 13 becomes elliptically polarized light, and is converted into intensity-modulated light by the analyzer 17 including the ¼ wavelength plate and the analyzer in the subsequent stage.

In this embodiment, the glass machine 1 provided with the resist layer 2 and the transmitted light limiting layer 3 is set to have a linear velocity of 1.2 m / sec at the exposure position by using the cutting machine having the above-mentioned structure. Rotated to. The exposure wavelength λ was 413 nm, and the numerical aperture NA of the objective lens 14 for condensing was 0.9.

The input power of the emitted laser light L is set to 2
The resist layer 2 was exposed to light at mW. The laser light transmitted through the transmitted light limiting layer 3 becomes about 1/10, which is a power sufficient for exposing the photoresist.

FIG. 4 shows the difference in beam profile between when the laser light L is focused on the resist layer 2 and when the transmitted light limiting layer 3 is provided. In FIG. 4, the solid line is the beam profile when the transmitted light limiting layer 3 is not present, and the broken line is the beam profile when the transmitted light limiting layer 3 is present.

As can be seen from FIG. 4, the resist layer 2
When the transmitted light limiting layer 3 made of a saturable dye is provided on the above,
The spot diameter of the laser light L is substantially 50%. This is the same effect that the wavelength of the laser light used for exposure is reduced to about half.

Therefore, after the above-mentioned exposure step, the resist layer 2 is developed to prepare an optical disk master, and for example, Ni electroforming is applied to the optical disk master to obtain a stamper, which is used to form a substrate material such as polycarbonate. By injection molding, it is possible to manufacture an optical disc in which minute phase pits are formed at high density.

Although the embodiment to which the present invention is applied has been described above, it goes without saying that the present invention is not limited to this embodiment. For example, the saturable dye or the like can be arbitrarily selected according to the wavelength of the laser beam used for exposure. Also, the thickness of the transmitted light limiting layer can be arbitrarily set according to the power of the laser light and the like.

[0030]

As is apparent from the above description, in the present invention, a transmitted light limiting layer containing a substance that transmits only light having a predetermined intensity or more is provided on the resist layer, and this transmitted light limiting layer is provided. Since the resist layer is exposed through the light, it is possible to form a dramatically small phase pit beyond the limit of λ / NA.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a resist forming process.

FIG. 2 is a schematic sectional view showing a step of forming a transmitted light limiting layer.

FIG. 3 is a schematic diagram showing a configuration example of a cutting machine.

FIG. 4 is a characteristic diagram showing a difference in beam profile of transmitted laser light depending on the presence or absence of a transmitted light limiting layer.

[Explanation of symbols]

 1 glass substrate 2 resist layer 3 transmitted light limiting layer

Claims (2)

[Claims] 1. A resist layer is formed on a substrate, and when the resist layer is selectively exposed according to an information signal and then developed to form phase pits, only light having a predetermined intensity or more is formed on the resist layer. A method of manufacturing an optical disk master, comprising providing a transmitted light limiting layer containing a substance that transmits light, and exposing the resist layer through the transmitted light limiting layer. 2. The method of manufacturing an optical disc master according to claim 1, wherein the substance that transmits only light having a predetermined intensity or more is a saturable dye.