Victor Company of Japan, Limited

Noboru Kawai

Tetsuya Kondo

Toshiro Abe

Kei Murata

An information recording disk for recording an information signal along a track defined by a depression on the disk as a change of physical property of a recording material deposited on the track comprises a disk-shaped glass substrate made of a glass and carries a groove corresponding to the track. The groove has a surface roughness substantially smaller as compared to the surface roughness caused at a bottom surface of a groove on a silica glass substrate when both the disk-shaped glass substrate and silica glass substrate are dry-etched under same conditions. The disk-shaped glass substrate comprises SiO.sub.2 component and one or both of Al.sub.2 O.sub.3 and BaO components with substantially no alkali components. Further, a recording layer comprised of the recording material which changes in physical property responsive to a projected energy beam is deposited on the substrate such that the depression is formed in correspondence with the track.

Information recording medium having a glass substrate

In a method of fabricating a master recording disc, a photoresist layer is formed on a glass substrate to form a master blank, which is revolved and exposed to an intensity-modulated laser beam so that a series of optically excited regions is formed in track turns in the photoresist layer. The optically excited regions are removed, forming a series of pits in the photoresist layer. An etchant gas is sputtered onto the master blank until the pits in the photoresist layer extend through the boundary surface of the photoresist layer and the glass substrate to a desired depth and pits having side walls tapered in a direction away from the boundary surface are formed in the substrate. The photoresist layer which remains on the glass substrate is finally removed.

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Komae, Japan

Noboru Kawai