JPH08227538A - Exposing master disk for optical disk and its production - Google Patents

Abstract

PURPOSE: To form plural kinds of pits varying in depth with good accuracy by a simple method. CONSTITUTION: This exposing master disk 10 has a substrate 52 having a flat surface 52a, a photoresist film 12 deposited on the surface 52a of this substrate 52 and many pits 14 bored in this photoresist film 12 by exposing and developing. This photoresist film 12 consists of two layers; photoresist films 121, 122. The pits 14 include two kinds; P11 , P12 ,... having the depth d1 from the surface 12a of the photoresist film 12 to the photoresist layer 121 and pits P21 , P22 ,... having depth d2 from the surface 12a of the photoresist film 12 to the photoresist layer 122. Two kinds of the pits varying in the depths are easily formed on the optical disk, by which writing of ternary data and increasing of the recording density thereof are made possible.

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 exposure master serving as a source of a nickel stamper for producing an optical disk, and more particularly to a method for manufacturing an exposure master suitable for increasing the density of an optical disk such as a CD-ROM. .

[0002]

2. Description of the Related Art FIG. 6 is a sectional view showing a conventional exposure master. The conventional exposure master 50 includes a substrate 52 having a flat surface 52a, a photoresist film 54 deposited on the surface 52a of the substrate 52, and a large number of pits 56 formed in the photoresist film 54 by exposure and development. It is equipped with and.

FIG. 7 is a sectional view showing a method of manufacturing the exposure master 50. First, a photoresist film 54 is formed by applying a photoresist to the flat surface 52a of the substrate 52.
Are formed (FIG. 7 (1)). Next, the photoresist film 5
4 is exposed to laser light L. As a result, the portion of the photoresist film 54 irradiated with the laser light L becomes the photosensitive portion 54a due to the photochemical reaction (FIG. 7 (2)). Finally, the photoresist film 54 is developed to remove the photosensitive portion 54a and form the pit 56 (FIG. 6).

[0004]

In recent years, there has been an increasing demand for higher density optical discs. As a means for increasing the density, it is possible to increase the storage density by providing a plurality of types of pits having different depths.

However, according to the conventional technique, in order to provide a plurality of types of pits having different depths, it is necessary to fabricate an exposure master by repeating the steps of coating, exposing, and developing a photoresist a plurality of times. Therefore, not only the process becomes extremely complicated, but also it is difficult to obtain a desired processing accuracy due to accumulated errors due to an increase in the number of processes and deterioration of the photoresist.

Therefore, an object of the present invention is to provide an exposure master that can form a plurality of types of pits having different depths with high accuracy by a simple method, and a method for manufacturing the same.

[0007]

An exposure master according to the present invention
Is a substrate with a flat surface and the surface of the substrate
The exposed photoresist film and this film by exposure and development.
Light with a large number of pits formed in the photoresist film
In the exposure master of the disc, The photoresist film
However, there are multiple photons with different sensitivity to the wavelength of the exposure light source.
A photoresist layer, the plurality of photoresist layers
The pits are stacked in ascending order of sensitivity
The plurality of photoresists are formed from the surface of the photoresist film.
Characterized by having a depth up to any of the
Of.

Here, the plurality of photoresist layers preferably have a sensitivity difference of about 5 times or more, and more preferably 10 times or more, with respect to a predetermined exposure light source wavelength.

Further, in the method of manufacturing an exposure master according to the present invention, a photoresist film is deposited on the flat surface of the substrate, the photoresist film is exposed to laser light, and the photoresist film is developed. In a method of manufacturing an exposure master for an optical disc having a large number of pits, a plurality of photoresist layers having different sensitivities to the wavelength of the laser light are stacked in order from the lowest sensitivity to form the photoresist film. It is characterized in that a plurality of exposure amounts are selected so that the surface of the photoresist film to any one of the plurality of photoresist layers can be exposed.

Here, it is preferable that the plurality of photoresist layers have a difference in sensitivity of about 5 times or more, and more preferably about 1 digit or more, with respect to a predetermined exposure light source wavelength. .

When a photoresist film formed by laminating a plurality of photoresist layers having different sensitivities is exposed, a photoresist layer that is exposed and a photoresist layer that is not exposed are formed according to the exposure amount. In this case, since the photoresist layers are laminated in the order of increasing sensitivity from the substrate side, the upper part of a certain photoresist layer is exposed and the lower part of the photoresist layer is not exposed.

[0012]

1 is a sectional view showing one embodiment of an exposure master according to the present invention. The present embodiment will be described below with reference to this drawing. However, the same parts as those in FIG. Note that, for convenience of illustration, the photoresist film 12 is shown in an enlarged scale as compared with the substrate 52.

The exposure master 10 according to the present invention has a substrate 52 having a flat surface 52a, a photoresist film 12 adhered to the surface 52a of the substrate 52, and a hole formed in the photoresist film 12 by exposure and development. Many pits
4 and.

The photoresist film 12 has a two-layer structure of photoresist layers 121 and 122. Pit 14
Pits P1 ₁ and P1 having a depth d1 from the surface 12a of the photoresist film 12 to the photoresist layer 121.
₂ , ..., and a pit P2 having a depth d2 from the surface 12a of the photoresist film 12 to the photoresist layer 122.
There are two types: 1, P2 ₂ , ... Therefore, the exposure master 10 is written with three-valued data: no pit, a pit having a depth d1, and a pit having a depth d2.

The photoresist layer 122 is made of photoresist # 1 (tentative name, hereinafter the same) or # 2, which is, for example, a g-line type photoresist, and the photoresist layer 121 is, for example, an i-line type photoresist. Which is photoresist # 3 or # 4. As shown below, each of the photoresists # 1 to # 4 is a positive type resist, and is composed of a mixture of a resin, a photosensitizer, and a solvent.

For example, a resin containing novolac as a main component is used as the resin, and a compound containing naphthoquinonediazide as the main component is used as the photosensitizer. Examples of the novolac resin include o-cresol novolac, m-cresol novolac, p-cresol novolac, and
Poly (4-hydroxystyrene), polyvinylphenol, etc. are used. Further, as the photosensitizer, 2-diazo ketone, orthodiazobenzoquinone, orthodiazonaphthoquinone or the like is used.

The characteristics of the photoresist differ depending on the molecular weight and molecular weight distribution of the novolac resin and the photosensitizer, and the ratio of the total weight to the photoresist. Photoresists # 1 to # 4
The data such as the molecular weight of is shown in Table 1.

[0018]

[Table 1]

In the above table, the resin content shows the ratio with respect to the total weight of the photoresist, and the photosensitizer content shows the ratio with respect to the resin weight. In addition, in the above table, the term "metal rich" means that the meta isomer is 7
It means that 0% or more is contained, and "metarich + α" means that, for example, the meta isomer is contained in 60% or more of the total amount.

Hereinafter, the above photoresists # 1, # 2, #
The optical characteristics of 3 and # 4 will be described. FIG. 2 shows the transmittance of the photoresist by exposure depending on the wavelength (nm) of the light source for exposure measured on the substrate, the photoresist # 1 for the g-line specification, and the photoresist # 3 for the i-line specification. 6 is a graph showing how (%) changes. From the measurement results of such transmittance, each photoresist # 1,
Parameters A and B of # 2, # 3, and # 4 are obtained.
Parameter A is the change in optical density per unit film thickness due to the exposure of the photoresist (Change value of optical de
Parameter B is the optical density of bleached resin and photo-acti
vity-compound). The parameters A and B are calculated by
Generally, according to the following formula.

A = (1 / d) · ln [T (∞) / T (0)] ... B = − (1 / d) · ln [T (∞)] ...

Where d is the film thickness of the photoresist and T
(0) is the transmittance before exposure (Unbleachedtransmision),
T (∞) is the transmittance after exposure saturation (Saturation bleached
transmision).

From the formula and the measurement result of the transmittance of each photoresist as shown in FIG.
The parameters A / B on the i lines of 1, # 2, # 3, and # 4 were obtained. The values are 1.23 / 0.31 and 1.22 /
The values were 0.13, 0.74 / 0.07, and 0.94 / 0.12. In addition,
The substrate used for measuring the transmittance is fused silica glass with a thickness of 0.5 mm, and the thickness of each photoresist is 100 nm.

FIG. 3 shows the results of measuring the relationship between the exposure dose (mJ ² ) and the resist residual film (%) for each photoresist, and shows the γ value characteristic curve of each photoresist. In this graph, a steep curve represents the cuttability of the photoresist. Each photoresist # 1, # 2, #
The γ values measured with ultraviolet rays of 3 and # 4 are 2.1, respectively.
0, 2.19, 2.14, and 1.58. Further, since the horizontal axis represents the exposure amount, g-line specification photoresists # 1, #
It can be seen that No. 2 has higher sensitivity than the photoresists # 3 and # 4 for i-line specification.

FIG. 4 shows the exposure amount (mW) by the master writer (optical disc exposure device) which employs the direct drawing method.
And the pit width (μm) formed thereby are shown for each photoresist, and this graph shows the exposure sensitivity characteristic of each photoresist. As is clear from the figure, the exposure sensitivity of the photoresist differs between the g-line specification and the i-line specification by about one digit. Therefore, if an exposure amount intermediate between the sensitivities of the photoresists of both these specifications is set, only the photoresist of the g-line specification is exposed,
The i-line type photoresist will not be exposed.

FIG. 5 is an explanatory view showing a method of manufacturing an exposure master according to one embodiment of the present invention. FIG. 5 (1) is a sectional view showing a photoresist coating step, and FIG. 5 (2) is exposure. FIG. 5C is a sectional view showing the steps, and FIG. 5C is a waveform diagram showing the exposure amount in the exposure step. As shown in FIG. 3C, the exposure amount is divided into three stages of zero exposure amount, exposure amount 1 and exposure amount 2 depending on the presence or absence of pits and the formation depth thereof. Hereinafter, the manufacturing method will be described with reference to FIGS. 1 to 5.

The substrate 52 is made of transparent glass. First,
On the surface 52a of the substrate 52, an i-line type photoresist #
3 or # 4 is applied to form a photoresist layer 121. Next, a photoresist # 1 or # 2 having a g-line specification is applied on the upper surface of the photoresist layer 121 to form a photoresist layer 122. As a result, the photoresist film 12 having a two-layer structure is formed on the substrate 52 (FIG. 5).
(1)). Then, pre-baking is performed at 80 to 100 ° C.

From FIG. 3, photoresist # 3 for i-line specification
It can be seen that the sensitivities are significantly different between the photoresists # 4 and # 4 and the photoresists # 1 and # 2 having the g-line specification. That is, FIG.
As is clear from the above, the photoresists # 1 and # 2 are exposed to light by an order of magnitude lower than that of the photoresists # 3 and # 4, and pits can be formed. Therefore, as the exposure amount by the laser light L, the wavelength λ = 363.8n
When m is used, the exposure amount 1 of 0.15 to 0.2 mW is used to expose only the photoresist layer 122 provided on the surface layer, and 1.5 to 2.0 mW is used to expose the two layers of the photoresist layers 121 and 122. An exposure amount of 2 will be used.

As shown in FIG. 5C, the surface of the photoresist film 12 is changed while selecting either of two kinds of exposure level 1 or exposure level 2 according to the depth of the pit to be formed.
The laser light L is sequentially exposed (FIG. 5 (2)). This exposure amount can be easily selected by changing the output intensity of the laser light L. Finally, due to the phenomenon, the photosensitive portions 211, 212, 221-224 are removed,
The exposure master 10 shown in FIG. 1 is completed.

Photoresist layer 12 in the present manufacturing method
Due to the relationship between the tracking servo and the RF signal, the film thicknesses of 1 and 122 are set so that the phase difference between the reproduced signals becomes maximum when the RF signal is reproduced. This film thickness is related to the wavelength of the reproducing light source. For example, when a near infrared laser diode with a wavelength λ = 800 nm is used, the total film thickness is λ / 4, that is, 130 nm (refractive index of the substrate 52 is 1.5). Then, the photoresist layer 122 is set to λ / 8 to λ / 4, that is, 65 nm to 130 nm. Alternatively, if the photoresist layer 122 is λ / 4, that is, 130 nm, the total film thickness is λ /
It is set to 4 to λ / 8, that is, around 130 to 195 nm.

Although the present invention has been described based on the preferred embodiments thereof, the exposure master of the optical disk of the present invention and the method for manufacturing the same are not limited to the configurations of the above-mentioned embodiments, and the above-mentioned embodiments are not limited thereto. An exposure master that is variously modified and changed from the configuration of the embodiment and a manufacturing method thereof are also included in the scope of the present invention. For example, instead of the structure of the above embodiment, three or more types of photoresist are applied to form a photoresist film having a multilayer structure of three or more layers, and three or more types are selected depending on the characteristics of these photoresist layers. The exposure amount may be selected for exposure.

[0032]

As described above, according to the present invention, since the photoresist films composed of a plurality of photoresist layers having different sensitivities to the exposure light source are sequentially stacked in the ascending order of sensitivity, a desired pit is formed. By selecting the exposure amount according to the depth, it is possible to easily and accurately form pits having a plurality of types of depths by a single exposure. By recording such multi-valued pit data on the optical disc, an optical disc capable of high density recording can be easily and inexpensively produced.

When the difference in sensitivity between the photoresists and the exposure light source is about 5 times or more, or 10 times or more, a plurality of types of pits having different depths can be formed with particularly good accuracy. .

[Brief description of drawings]

FIG. 1 is a sectional view showing one embodiment of an exposure master according to the present invention.

FIG. 2 is a graph showing the results of measuring the transmittance of a substrate and a photoresist used in the exposure master of FIG. 1 before and after exposure.

3 is a graph showing a measurement result of a γ value characteristic curve of each photoresist used for the exposure master of FIG. 1. FIG.

FIG. 4 is a graph showing exposure sensitivity characteristics by a master writer of each photoresist specified for the exposure master of FIG.

5A and 5B are explanatory views showing a method for manufacturing the exposure master of FIG. 1, wherein FIG. 5A is a sectional view showing a photoresist coating step, FIG. 5B is a sectional view showing an exposure step, and FIG. 3) is a waveform diagram showing the exposure amount in the exposure step.

FIG. 6 is a cross-sectional view showing a conventional exposure master.

7A and 7B are explanatory views showing a conventional method of manufacturing an exposure master, FIG. 7A is a sectional view showing a photoresist coating step, and FIG. 7B is a sectional view showing an exposure step.

[Explanation of symbols]

10 exposed master 12 photoresist film 121 and 122 a photoresist layer _{14, P1 1, P1 2,} P2 1, P2 2 pit 52 substrate 52a surface of the substrate

Claims (4)

[Claims] 1. Exposure of an optical disc comprising a substrate having a flat surface, a photoresist film deposited on the surface of the substrate, and a large number of pits formed in the photoresist film by exposure and development. In the master, the photoresist film is composed of a plurality of photoresist layers having different sensitivities to the wavelength of the light source for exposure, the plurality of photoresist layers are stacked in the ascending order of the sensitivity, and the pits are the photoresist film. An exposure master of an optical disc having a depth from the surface of the photoresist to any one of the plurality of photoresist layers. 2. The exposure master of an optical disc according to claim 1, wherein the plurality of photoresist layers have a sensitivity difference of about 5 times or more as to a predetermined exposure light source wavelength. 3. An optical disk master for exposing a photoresist film on a flat surface of a substrate, exposing the photoresist film with a laser beam, and developing the photoresist film to form a large number of pits. In the manufacturing method, a plurality of photoresist layers having different sensitivities to the wavelength of the laser light are sequentially stacked from the one having the lowest sensitivity to form the photoresist film, and the plurality of photoresist layers are formed from the surface of the photoresist film. A method for manufacturing an exposure master for an optical disc, which comprises: selecting a plurality of exposure amounts capable of exposing any one of the photoresist layers and performing exposure. 4. The method according to claim 3, wherein the plurality of photoresist layers have a sensitivity difference of about 5 times or more with respect to a predetermined exposure light source wavelength. .