Information recording medium having a glass substrate

Claim 1

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 comprising: a disk-shaped glass substrate made of a glass defined by a flat first surface at a first side and a second surface carrying a groove corresponding to the track at a second side opposite to the first side, said groove being defined by a bottom surface having 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, and said disk-shaped glass substrate comprising SiO 2 component and one or both of Al 2 O 3 and BaO components while free from those alkali and alkali earth elements having one or more elements selected from a group consisting of sodium, magnesium, potassium, and calcium; a recording layer comprised of the recording material which changes in physical property responsive to a projected energy beam modulated with the information signal, said recording layer deposited on the second surface of the substrate having one side thereof making an intimate contact with the second surface, said recording layer carrying said depression which defines the track on other side of the recording layer; and a protection layer deposited on said another side of the recording layer so that the depression on the recording layer is buried under the protection layer with an intimate contact between the protection layer and the recording layer.

Claim 12

A method of manufacturing an information recording disk for recording an information signal along a track defined by a depression as a change of physical property of a recording material deposited on the depression comprising steps of: applying a photoresist on a surface of a disk-shaped glass substrate made of a glass free from those alkali and alkali earth elements having one or more elements selected from a group consisting of sodium, magnesium, potassium, and calcium; exposing the photoresist to a radiation of energy beam so as to write a pattern on the photoresist by the radiation, developing the photoresist and removing a portion of the photoresist irradiated by the radiation from the surface of the glass substrate; subjecting the glass substrate to an etching at an etching rate substantially slower than an etching rate which is obtained when a silica glass is etched under a same etching condition and forming a groove deep into the glass substrate at a portion of the surface of the glass substrate which is not covered by the photoresist after the etching, said groove formed by the dry etching being corresponding with the depressions defining said track removing a remaining photoresist from the surface of the glass substrate; depositing the recording material, physical property thereof is transformable responsive to further radiation of energy beam modulated with the information signal, on the surface of the glass substrate to form a recording layer such that the depression which defines the track is formed on a surface of the recording layer in correspondence with the groove at the surface of the glass substrate; and depositing a protection layer on the surface of the recording layer for protecting the depression at the surface of the recording layer.

Claim 13

A method of manufacturing an information recording disk for recording an information signal along a track defined by a depression as a change of physical property of a recording material deposited on the depression comprising steps of: applying a photoresist on a surface of a disk-shaped glass substrate made of a glass free from those alkali and alkali earth elements having one or more elements selected from a group consisting of sodium, magnesium, potassium, and calcium; exposing the photoresist to a radiation of energy beam so as to write a pattern on the photoresist by the radiation, developing the photoresist and removing a portion of the photoresist irradiated by the radiation from the surface of the glass substrate; subjecting the glass substrate to an etching at an etching rate substantially slower than an etching rate which is obtained when a silica glass is etched under a same etching condition and forming a groove deep into the glass substrate at a portion of the surface of the glass substrate which is not covered by the photoresist after the etching, said groove formed by the dry etching being corresponding with the depressions defining said track removing a remaining photoresist from the surface of the glass substrate; depositing the recording material, physical property thereof is transformable responsive to further radiation of energy beam modulated with the information signal, on the surface of the glass substrate to form a recording layer such that the depression which defines the track is formed on a surface of the recording layer in correspondence with the groove at the surface of the glass substrate; and depositing a protection layer on the surface of the recording layer for protecting the depression at the surface of the recording layer.