Optical recording medium, and method of manufacturing same

Abstract

There are provided an optical recording medium and a method of manufacturing the optical recording medium. The optical recording medium has a pattern of microscopic depressions and projections molded thereon with a high fidelity of replication. The method of manufacturing the optical recording medium comprises the steps of forming a photoresist layer on a substrate; exposing a predetermined area of the photoresist layer formed on the substrate to form a plurality of trains of depressions in the photoresist layer; removing the photoresist layer between the adjoining depression trains to form a master; plating the master with a metal; separating the metal coating to form a master stamper; replicating the master stamper repeatedly an odd number of times to form a mother stamper; replicating the mother stamper to form a resin substrate; and forming at least a light-transparent layer on a surface of the resin substrate on which the mother stamper is replicated. The method can mold a pattern of microscopic depressions and projections with a high accuracy.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to an optical recording medium comprising a substrate having formed thereon a pattern of depressions and projections and a light-transparent layer formed on the substrate, and a method of manufacturing the optical recording medium.[0003] 2. Description of Related Art[0004] As typical conventional optical recording media from or into which data is read or written using a light, ones shaped to have a generally disc-like form, so-called optical discs, are well known of which an optical disc substrate is formed from a synthetic resin such as polycarbonate or similar. The optical discs include a read-only type from which a signal already recorded therein can be read, a write-once type into which a signal can be recorded only once, and a rewritable one into which a signal can be recorded more than once.[0005] The read-only type optical disc comprises an optical disc substrate having a pattern of microscopic depressions (...

AI Technical Summary

Problems solved by technology

Also, the thicker a disc portion through which a reading light is transmitted, the larger the aberration due to the tilt angle will become.

In the above-mentioned optical disc, however, it is difficult to mold a pattern of depressions and projections on an optical disc substrate having a thickness of 0.3 mm or less, for example.

Further, even if the molding is possible, the optical disc substrate is likely to warp, which will result in a difficulty in forming thereon layers such as recording layer, reflective layer, etc.

Moreover, if the optical disc substrate having such a thickness, the user will not be able to easily handle an optical disc made from the optical disc substrate.

Actually, however, it is difficult to fully charge such a lower-density resin into microscopic depressions.

Namely, it is not possible to mold pits with a high accuracy.

This means that for example, with depressions formed intermittently in the direction of track on the stamper correspondingly to pits on an optical disc substrate, it is difficult to form microscopic pits.

Furthermore, a mold at a high temperature will be expanded itself, which will cause the molding machine to malfunction.

If the mold is thermally expanded too much, the moving piece of the mold will incur a so-called galling with a result that the molding machine will possibly damaged.

The manufacture of the read-from-rear optical disc is disadvantageous in that the projections formed as additional signals cannot be replicated with a high accuracy, which will lead to a low yield and thus the additional signals could not be read accurately from the corresponding projections not precisely replicated.

However, if the thickness t of the substrate 101 of the conventional optical disc 100 is decreased, microscopic depressions and projections cannot easily be replicated to the substrate 101 and also the substrate 101 itself will easily warp.

However, if the track pitch is decreased for a higher recording density, a sufficient increase of the groove width Wg for a good CN ratio will be physically impossible.

Therefore, in this case, a sufficiently wide signal recording surface is not available within the track pitch.

As a result, signal cannot stable be read from the signal recording surface of an optical disc thus produced.

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