JP2519987B2 - Glass master for optical disc manufacturing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention manufactures a read-only optical disc such as a video disc and a digital audio disc, a writable or rewritable optical disc used for an image file, a document file, a computer external memory and the like. The present invention relates to a glass master used for

[Conventional technology]

The mastering process of an optical disc is a process of forming a prototype of an optical disc by coating a polishing glass plate with a resist, exposing it with a laser beam and developing it to form pits corresponding to tracking grooves and signals. The glass master used here is usually a disc with a diameter of 200-350 mm and a thickness of 6-10 mm.
Depending on the method of fixing the master to the turntable when performing laser exposure, a master having a through-hole, a non-through-hole, or no hole is used. The front and back surfaces are mirror finished. Since surface defects are sequentially transferred to the stamper and optical disc substrate, the surface is usually polished to the limit so that there is no defect, and the surface roughness is 10 Å or less, which is close to the detection limit of the surface roughness by the diamond stylus method. There is. Chamfers or roundness of 1.0 mm or less are provided at the upper and lower outer peripheral edges of the disc, and it is usual to apply a chamfer or a roundness to avoid the risk of becoming the starting point of damage to the entire disc. If there is a central hole, finish the upper and lower ends in the same way. In the prior art, the outer peripheral side surface and the central hole wall surface were not polished including chamfered portions or rounded portions, and were usually used as they were as rough surfaces.

[Problems to be solved by the invention]

However, in the above-mentioned conventional technique, after the glass master is surface-polished with an abrasive such as cerium oxide, fine particles of the abrasive remain adhered and remain on the outer peripheral side surface of the glass master and the rough surface portion of the inner wall of the center hole in the cleaning step, which is a subsequent step. At the same time, it moved and adhered to the surface of the glass master, causing defects in the stamper created.

Furthermore, after nickel electroforming, when the nickel stamper is peeled off from the glass master, the nickel film attached to the rough surface of the glass master does not easily peel off, and the glass master is often damaged. There was no possibility of reuse.

[Means for solving problems]

As a result of earnest studies, the inventors have invented means for solving the above problems. That is, by polishing the outer peripheral side surface of the glass master and the rough surface of the inner wall of the center hole to be a mirror surface, fine particles of the polishing agent did not remain, and the nickel film was easily peeled off after electroforming.

For polishing the rough surface, known methods for polishing glass such as a method of rubbing with synthetic leather using a suspension agent of cerium oxide in water and a method of gradually polishing from coarse to dense with sandpaper can be used. Rotating or translating a polishing tool or an object to be polished to facilitate polishing or to automate the polishing is also preferable from the viewpoint of production capacity. The required smoothness of the mirror surface can be determined by visual inspection, but it is preferably 0.01 S or less as measured by a diamond stylus type surface roughness meter.

In order to achieve the object of the present invention, it is preferable that the chamfer or the rounded portion provided on the outer periphery and the central hole is also polished so as to have smoothness corresponding to an acute surface.

 Examples will be described below more specifically with reference to the drawings.

〔Example〕

FIG. 1 is a schematic view of a cross section of a glass master according to the present invention.
With a soda glass with a diameter of 200 mm, a central hole diameter of 10 mm, and a thickness of 6 mm,
The front surface 1, the back surface 1 ', the outer surface 2, the inner wall surface 3 of the center hole, and the chamfers (0.5C) at the outer periphery and the upper and lower ends of the center hole are mirror-polished. After cleaning and drying this glass master, a uniform resist film is formed on the surface, scanning exposed by a laser beam on a turntable, and developed to develop a width of 0.6μ, a depth of 800Å,
Tracking grooves with a pitch of 1.6μ were formed spirally. (FIG. 2) A conductive film was formed on this resist master by an electroless nickel method, and nickel electroforming was performed to obtain a nickel replica having a thickness of 0.3 mm.
(FIG. 2) The back surface of the replica was polished, the outer diameter was trimmed, and the center hole was formed with predetermined dimensions to obtain a stamper.
Peeling was extremely smooth, and the defect rate of the disk substrates molded using this stamper was in the range of 1 to 5 × 10 ⁻⁶ when measured on 10 sheets.

[Comparative example]

A stamper was prepared under the same conditions except that the side surface was not polished. When the stamper is peeled off from the glass master, the outer periphery and the center hole have visually observable scratches, and the master surface also has scratches or defects that may be derived from abrasive particles. Injection molding using this stamper The defect rate of the prepared disk substrates was measured for 10 and was in the range of 1 to 6 × 10 ⁻⁴ .

〔The invention's effect〕

Thus, by polishing the outer peripheral side surface and the central hole wall surface of the glass master for optical disk mastering, the polishing agent does not remain and does not cause defect formation, and the electroformed product can be easily peeled from the master. It is extremely rare to damage the board and make it unplayable.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a typical polished glass master, and FIG. 2 is a schematic view of a cross section after nickel electroforming is performed on this glass master. 1 ... Polished glass surface, 1 '... Polished glass back surface, 2 ...
... outer peripheral side surface, 3 ... center hole wall surface, 4 ... soda glass,
5: Resist groove, 6: Nickel electroformed replica.

Claims (1)

(57) [Claims] 1. A glass master for use in an optical disk mastering process, characterized in that an outer peripheral side surface and a central hole wall surface are mirror surfaces.