JPH0626820B2 - Optical disk substrate manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] As a method of forming an optical disk substrate with a guide groove by a photopolymer method with a low defect rate, a transfer mold heated by UV irradiation is cooled to a temperature before UV irradiation and used. Optical disk substrate manufacturing method.

[Field of Industrial Application] The present invention relates to a method for manufacturing an optical disk substrate in which a guide groove is formed using an ultraviolet curable resin.

Optical discs are classified into so-called optical discs and magneto-optical discs, both of which are memories that perform high-density information recording using laser light, have a large recording capacity, and are capable of non-contact recording and reproduction. It also has excellent features such as being unaffected by dust.

That is, the laser beam can be focused by a lens into a small spot having a diameter of about 1 μm.
The area required for recording information of bits is about 1 μm ² .

In addition, since the distance to the focal plane of the laser beam focused by the lens can be 1 to 2 mm, it can be made non-contact, and the diameter of the light beam on the substrate surface is about 1 mm. Even if there is dust with a size of 10 μm ² , recording and reproduction can be hardly affected.

Here, an optical disc uses a low melting point metal as a recording medium, and a read-only memory (Read Only Memory) or a write-once type memory (Wri
te Once Memory), and rewritable memory (Erasable Memo) that records and plays using changes in reflectance.
There are various things such as (ry).

On the other hand, a magneto-optical disk is a rewritable memory (Erasabl
e memory), the recording medium consists of a perpendicularly magnetized magnetic film, and the magnetization reversal due to the temperature rise of the laser-irradiated magnetic film is used for recording and erasing information. Reproduction is performed by utilizing the fact that the rotation of the plane of polarization of reflected light or transmitted light differs depending on the magnetization direction.

The present invention relates to a method for manufacturing a substrate that constitutes such an optical disc.

[Conventional technology]

The substrate forming the optical disk is glass or polymethylmethacrylate (abbreviation PMMA), polycarbonate (abbreviation P
It is made of transparent plastic such as C) and is used with a concentric or spiral guide groove (pre-group).

Here, the guide groove is a place where information is recorded, and is formed on the optical disc substrate with a width of 0.7 μm, a depth of 0.07 μm, and a pitch of 1.6 μm. In this situation, the laser beam focused to a diameter of about 1 μm is irradiated along this guide groove to record / reproduce and erase information.

The method of manufacturing the optical disk substrate with the guide groove differs depending on the substrate material, but the following method is used.

A method in which molten PMMA or PC resin is cast into a transfer mold with guide grooves formed in advance.

After applying a UV-curable resin (photopolymer) on a smooth transparent substrate made of glass or plastic, press-fit the mold with the guide groove and irradiate it with ultraviolet rays through the transparent substrate to cure it. A method of forming them integrally.

A method in which a glass substrate is coated with a photoresist, selectively exposed, developed, and etched by a photo-etching technique (photolithography).

This method is called the 2P method, is suitable for mass production, and is generally used because it has good quality.

The present invention relates to improvements in this method.

FIGS. 2A to 2D are sectional views for explaining the 2P method, and the manufacturing process will be described as follows.

First, the ultraviolet curable resin 3 is piled up on the guide groove 2 of the transfer mold (commonly called stamper) 1 made of nickel (Ni) in which the guide groove is formed. (A in the figure) Next, the transparent substrate 4 is placed and positioned on this, and the transparent substrate 4 is pressed. (B in the figure) Next, the ultraviolet curable resin 3 is cured by irradiating the ultraviolet ray 5. Next, by peeling the transparent substrate 4 from the transfer mold 1, the optical disc substrate 8 having the guide groove 2 can be obtained.
(D in the same figure) However, the problem with this method is that if the bubble 6 exists in the ultraviolet curable resin 3 and its position is in the position of the guide groove 2 as shown in FIG. Width is about 0.7
Since it is as narrow as μm, a defect 7 occurs as shown in FIG.
In addition, the problem of defocusing occurs.

Now, in the manufacture of optical disks, the optical disk substrate 8 using an ultraviolet curable resin is repeatedly used by using the transfer mold 1, but the bubble generation tends to increase with continuous use, and this solution has been desired. .

[Problems to be solved by the invention]

As described above, when forming an optical disk substrate with a guide groove using an ultraviolet curable resin, defects due to the presence of air bubbles are likely to occur, and this is a problem especially when the transfer mold is used continuously. .

[Means for solving problems]

The above problem is that a photo-curing resin is placed on a transfer mold having a guide groove formed therein, ultraviolet rays are radiated while pressing a smooth transparent substrate against the transfer mold, and the photo-curing resin is polymerized to be integrated and guided. In a manufacturing process of an optical disk substrate in which a transparent substrate with a groove is repeatedly formed, it can be solved by a manufacturing method of an optical disk substrate in which a transfer mold heated by UV irradiation is cooled to a temperature before UV irradiation and used. The present invention has been made as a result of the discovery that the decrease in the viscosity of the photopolymer is closely related to the increase in bubbles when the guide groove is formed by the 2P method.

That is, to form the guide groove, it is necessary to keep the viscosity of the UV curable resin used at 100 to 200 CPS (centipoise), but as the number of times of use increases, the temperature of the transfer mold increases due to the preheating of UV irradiation, Therefore, it was found that the decrease in the viscosity of the supplied ultraviolet curable resin is a cause of the generation of bubbles.

In order to form the guide groove without the inclusion of bubbles by the 2P method, it is necessary to build up the ultraviolet curable resin 3 on the disc-shaped transfer type guide groove 2 as shown in FIG. 2 (A). Therefore, the viscosity should be high.

On the other hand, UV curable resin needs to be filtered prior to use in order to remove dust and oligomers contained in it.From this point, it is better that the viscosity is low, and from this tradeoff, the viscosity used is 100-200 CPS. It is restricted.

However, the temperature of the transfer mold has risen after the UV-curable resin has been cured by irradiating it with ultraviolet rays. For example, if the temperature before irradiation was 25 ° C, the temperature rises to 32 ° C, and the heat capacity is large. Because of this, the temperature does not drop to room temperature.

Therefore, when the same transfer mold is used and the process shown in FIG. 2 is repeated, the temperature of the transfer mold gradually rises, and the frequency of bubble inclusion increases proportionally.

Therefore, in the present invention, the transfer die is cooled and returned to room temperature after each use, or the transfer die is attached to a cooling device such as a water cooling device and the 2P method shown in FIG. It suppresses.

〔Example〕

A Ni stamper with a diameter of 190 mm and a thickness of 0.3 mm has a thickness of
A reinforced with a 15 mm aluminum (Al) disk was used as a transfer mold, and an acrylic acid ester (product name SA1002) manufactured by Mitsubishi Yuka was used as an ultraviolet curable resin.

The viscosity is 100 cps at 25 ° C.

A glass plate having a thickness of 1.2 mm and a diameter of 200 mm was used as the transparent substrate.

The manufacturing process is as shown in FIG. 2, and the time required for each process of resin supply, transparent substrate mounting, ultraviolet irradiation, and peeling is set to 1 minute, and the type is divided into two, one of which is related to the present invention. As described above, the transfer die was forcibly cooled to room temperature every cycle, and the other one was produced as usual.

The irradiation of ultraviolet rays was 120 W / cm, and the distance between the light source and the glass substrate was kept at 20 cm.

FIG. 1 is a diagram showing the relationship between the error rate measured on the optical disc formed in this manner and the number of times of transfer. The error rate sharply increases as shown by the broken line 9 in the case of the conventional method. According to the method, the value of about 5 × 10 ⁻⁷ could be maintained as shown by the solid line 10.

〔The invention's effect〕

As described above, even if the transfer mold is repeatedly used by implementing the present invention, it is possible to suppress an increase in the error rate, and thus it is possible to improve the manufacturing yield.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the number of transfers of a prototype optical disc and the error rate, and FIGS. 2 (A) to 2 (D) are sectional views for explaining the 2P method. In the figure, 1 is a transfer type, 2 is a guide groove, 3 is an ultraviolet curable resin, 4 is a transparent substrate, 5 is ultraviolet rays, 6 is a bubble, 7 is a defect, and 8 is an optical disk substrate.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasumasa Iwamura 1015 Kamiodanaka, Nakahara-ku, Kawasaki-city, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Mitsuyo Maeda 1015, Kamiodanaka, Nakahara-ku, Kanagawa Prefecture, Fujitsu Limited

Claims (1)

[Claims] 1. An ultraviolet curable resin is placed on a transfer mold having a guide groove formed therein, and ultraviolet rays are applied to the transfer mold while pressing a smooth transparent substrate, and the ultraviolet curable resin is polymerized and integrated, A method for manufacturing an optical disk substrate, characterized in that in a manufacturing process of an optical disk substrate in which a transparent substrate having a guide groove is repeatedly formed, a transfer mold heated by ultraviolet irradiation is cooled to a temperature before ultraviolet irradiation and used.