JP3480029B2 - Glass substrate for making optical disc masters - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate for producing an optical disc master used in an optical disc master producing process (so-called mastering process).

[0002]

2. Description of the Related Art An optical disk master is prepared by applying a photoresist on a glass substrate, exposing and developing the photoresist to form a predetermined pattern on the photoresist on the glass substrate. , An optical disk master making process, a so-called mastering process.

In the mastering process, so-called soda lime glass, which is soda lime glass, is generally used as the above-mentioned glass substrate, and it is used for manufacturing a master disc such as a digital audio disc or a video disc.

On the other hand, in the rewritable optical disk using the magneto-optical effect, the C / N of the magneto-optical signal which is not present in the above digital audio disk and video disk is important,
Improving C / N is a major issue in disc quality. In particular, the improvement of C / N is indispensable for promoting higher density.

[0005]

By the way, in general, C
In order to improve / N, it is necessary to increase the carrier level (C) or reduce the noise (N). Of the C / N characteristics, the carrier level (C) is mostly determined by the recording film, but the noise (N) largely depends on the surface shape of the master (surface state of the land or groove).

Under the circumstances, the inventors of the present invention have made various studies and found that the surface shape of the master is closely related to the amount of alkali contained in the glass substrate used for preparing the master. Things have become clear from experiments.

Therefore, in order to reduce the noise of the magneto-optical signal, it is not appropriate to use soda lime glass, which has been widely used in the past, for making a master, and it is necessary to use a glass substrate with a reduced alkali content. .

Since the quartz glass substrate contains almost no alkali, it is considered to be effective in reducing the noise. For example, in Japanese Patent Laid-Open No. 63-50935, the quartz glass substrate is actually used as an optical disk. An example adopted for a glass substrate for making a master is described.

This quartz glass substrate is very expensive,
If it is used as an optical disc master, the manufacturing cost will increase significantly.

The present invention has been proposed for the purpose of eliminating the disadvantages of the prior art. That is, it is an object of the present invention to provide a glass substrate for producing an optical disc master, which can produce an optical disc master with less deterioration of the surface shape and can produce a high-quality magneto-optical disc having a high C / N. And Another object of the present invention is to provide a glass substrate for producing an optical disc master, which can suppress the influence of alkali even when a glass having a high alkali content is used and which can reduce the manufacturing cost of the optical disc. And

[0011]

The present invention achieves the above-mentioned object by suppressing the amount of alkali on the glass substrate surface.

[0012]

That is, for the optical disc master according to the present invention
In the glass substrate, Na near the surface of the soda lime glass substrate is replaced with K by low temperature ion exchange to form a strengthening layer on the surface of the soda lime glass substrate that restricts movement of alkali or alkali ions in the soda lime glass substrate. It was done.

[0014]

[0015]

The chemical strengthening method used in the present invention is a strengthening method by ion exchange of an alkali metal on the surface of a glass substrate, which is larger than the alkali ion (sodium ion) contained in the glass in a temperature range not exceeding the glass transition point. The ion-exchanged strengthening layer is formed on the surface of the glass substrate by low temperature type ion exchange that is brought into contact with a molten salt of alkali ions (potassium ions) having an ionic radius. The thickness of the reinforcing layer (layer to be ion-exchanged) formed by this chemical strengthening method is 10 μm or less.

In the present invention, any glass can be used as the base glass substrate, but soda lime glass (soda lime glass) containing a large amount of sodium and inexpensive.
When used, the economic effect is great.

[0018]

As shown in FIG. 1, the amount of alkali contained in the glass substrate for producing an optical disk master is closely related to the noise level, and the noise level rapidly increases as the amount of alkali increases.

Blue plate glass contains 1 alkali (sodium)
It contains about 3 to 14% by weight, and if it is used as it is in the mastering process, the noise level becomes high.

[0020]

In the present invention, the strengthening layer formed on the surface of the glass substrate restricts the movement of alkali or alkali ions in the glass substrate, and as a result, the amount of alkali on the surface of the glass substrate decreases, so that the noise level is also reduced. A low optical disc master is created.

[0022]

EXAMPLES Examples to which the present invention is applied will be described in detail below based on concrete experimental results.

An optical disk master was prepared according to a normal optical disk master manufacturing process (mastering process), and the relationship between the amount of alkali in the glass substrate and the noise level was investigated. The experiment was performed according to the method described below.

The glass substrates prepared are the following five types. <Glass substrate used> Glass substrate A: Soda lime glass (Asahi Glass Co., Ltd., trade name AS) Glass substrate B: Low expansion glass (Asahi Glass Co., Ltd., trade name A
X) Glass substrate C: Alkali-free glass (Asahi Glass Co., Ltd., trade name AN) Glass substrate D: Glass substrate A chemically strengthened. Glass substrate E: A glass substrate A having a SiO ₂ film formed on its surface.

The glass substrate D was obtained by replacing Na in soda lime glass with K by a chemical strengthening method (low temperature type ion exchange). As shown in FIG. 2, K was substituted in the vicinity of the surface of the glass substrate 1. The reinforcing layer 1a is formed. When the thickness (depth replaced with K) of the reinforcing layer 1a was measured by the Auger method, it was 5 μm or less.

The glass substrate E has a SiO ₂ coating 2 formed on the surface of a glass substrate 1 made of soda lime glass as shown in FIG. 3 by applying a coating solution for forming a SiO ₂ coating and baking. Is. here,
As a coating liquid for forming SiO ₂ film, manufactured by Tokyo Ohka Kogyo Co., Ltd.
Using the product name OCD-Type 7 (10%), 1000r
After spin coating with pm, baking was performed at 200 ° C. for 60 minutes. The thickness of the SiO ₂ coating was about 0.5 μm.

Using the above-mentioned five types of glass substrates, a master for magneto-optical disks (ISO standard) having a diameter of 130 mm was prepared by a normal mastering process.

The mastering process will be briefly described. First, as shown in FIG. 4A, a photoresist is applied to the surface of the glass substrate 11 to form a resist layer 12.

Next, as shown in FIG. 4B, exposure (cutting) with a laser beam is performed, and as shown in FIG. 4C, development processing is performed to form irregularities according to signals on the resist layer 12.

Next, as shown in FIG. 4D, the resist layer 1
A thin conductive film 13 is formed on the surface 2 by silver plating, for example, and a metal master 14 is formed by Ni electroforming as shown in FIG. 4E.

In this example, the metal master 14 is used as an optical disc master (stamper), and an optical disc is prepared by ultraviolet curing using a photo-curing resin (so-called 2P).
Optical disk substrate was prepared according to the method).

Al is evaporated as a reflection film on the optical disk substrate prepared by the above process to form an optical disk, and the pregroove is returned by a signal measuring instrument having a laser light wavelength 830 nm / numerical aperture 0.53 / circularly polarized light pickup. The light was measured and used as the noise level. The noise level is the amplifier noise ratio (d) of the noise component in the return light of the groove.
B). The measurement frequency is 1 MHz to 5 MHz.

The results are shown in FIG. The numbers given to the circles in the figure correspond to the types of glass substrates used.

As is apparent from FIG. 1, the noise level increases as the amount of alkali in the glass substrate increases, but when the glass substrates D and E are used (corresponding to the embodiment). Since the amount of alkali on the surface of the glass substrate is suppressed, the noise level is suppressed to the same level as when the non-alkali glass substrate (glass substrate C) is used.

[0035]

As is apparent from the above description, in the present invention, N near the surface of the soda lime glass substrate is applied to the surface of the soda lime glass substrate by low temperature ion exchange.
By providing a reinforcing layer formed by replacing a with K,
By suppressing the amount of alkali on the surface of the soda lime glass substrate, it is possible to create an optical disk master with a low noise level.
It is possible to obtain a high-quality optical disc having a high C / N, especially a magneto-optical disc. Generally, when the carrier is increased to improve the C / N in the recording film structure, the so-called lifetime is reduced, but in the present invention, such a lifetime is not reduced.

Further, even if an inexpensive glass substrate having a high alkali content is used, an optical disc master having a low noise level can be produced, which is advantageous in terms of manufacturing cost.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between an amount of alkali in a glass substrate and a noise level.

FIG. 2 is a schematic sectional view of a glass substrate having a reinforcing layer formed on its surface by a chemical strengthening method.

FIG. 3 is a schematic cross-sectional view of a glass substrate having a SiO ₂ -based coating formed on its surface.

FIG. 4 is a schematic view showing a mastering process in process order.

[Explanation of symbols]

1 glass substrate, 1a strengthening layer, 2 SiO ₂ based coating

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kiyoe 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Kyoko Tada 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Within Sony Corporation (56) Reference JP-A-58-45997 (JP, A) JP-A-62-102445 (JP, A) Actual development Sho-62-180324 (JP, U) (58) Fields investigated ( Int.Cl. ⁷ , DB name) G11B 7/26 G11B 7/24

Claims (2)

(57) [Claims] 1. A low temperature ion exchange replaces Na in the vicinity of the surface of a soda lime glass substrate with K, and a strengthening layer for restricting migration of alkali or alkali ions in the soda lime glass substrate is formed on the surface of the soda lime glass substrate. A glass substrate for an optical disc master, which is formed. 2. The glass substrate for making a disk master according to claim 1, wherein the reinforcing layer has a thickness of 10 μm or less.