Optical information recording medium and method of producing a master and stampers therefor

Abstract

New and unobvious techniques for manufacturing optical information recording media (such as a phase-change type optical disc), including techniques for producing a master and stampers for producing the optical information recording media, are provided. Exposure light beams are controlled to form information recording tracking tracks and phase pits reliably and precisely.

1 . An optical information recording medium comprising: 
 information recording tracks configured to serve as grooves; and    phase pits formed on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other,    wherein preformatted information is recorded as said phase pits.    
   
   
       2 . An optical information recording medium comprising: 
 grooves configured to serve as information recording tracks; and    phase pits formed on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other,    wherein preformatted information is recorded as said phase pits, and    wherein a track center of the grooves and a center of the phase pits are substantially identical, gap widths of the grooves and the phase pits are substantially identical, and gap depths of the grooves and the phase pits are substantially identical.    
   
   
       3 . An optical information recording medium comprising: 
 grooves configured to serve as information recording tracks; and    phase pits formed on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other,    wherein preformatted information is recorded as said phase pits, and    wherein a center of the phase pits is radially displaced relative to a track center of the grooves, a gap width of the phase pits is greater than a gap width of the grooves such that each of the phase pits leaves a radial clearance from an immediately adjacent one of the grooves, and gap depths of the grooves and the phase pits are substantially identical.    
   
   
       4 . An optical information recording medium comprising: 
 grooves configured to serve as information recording tracks; and    phase pits formed on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other,    wherein preformatted information is recorded as said phase pits, and    wherein a center of the phase pits is radially displaced relative to a track center of the grooves such that each of the phase pits leaves a radial clearance from an immediately adjacent one of the grooves, gap widths of the grooves and the phase pits are substantially identical, and gap depths of the grooves and the phase pits are substantially identical.    
   
   
       5 . An original medium exposing method for producing the optical information recording medium of  claim 2 , said method comprising the steps of: 
 arranging a groove exposure beam at a track-center oriented position;    arranging a phase pit exposure beam at a place radially displaced from a track center;    conducting a groove exposure with the groove exposure beam; and    conducting a phase pit exposure substantially simultaneously with the groove exposure,    wherein in a time of the phase pit exposure, a light amount of the groove exposure beam is reduced, and a light amount of the phase pit exposure beam is smaller than the reduced light amount of the groove exposure beam.    
   
   
       6 . An original medium exposing method for producing an optical information recording medium, said method comprising the steps of 
 conducting a groove exposure for exposing an original medium with an exposure beam by arranging the exposure beam at a track-center oriented position; and    conducting a phase pit exposure for exposing the original medium with the exposure beam slightly displaced in a radial direction from the track-center oriented position,    wherein a light amount of the phase pit exposure is reduced from a light amount used in the groove exposure,    wherein, in the optical information recording medium, grooves serve as information recording tracks and phase pits are formed as preformatted information on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other, and    wherein a center of the phase pits is radially displaced relative to a track center of the grooves, a gap width of the phase pits is smaller than a gap width of the grooves, and gap depths of the grooves and the phase pits are substantially identical.    
   
   
       7 . An original medium exposing method for producing the optical information recording medium of  claim 3 , said method comprising the steps of: 
 arranging a groove exposure beam at a track-center oriented position;    arranging a phase pit exposure beam at a place radially displaced from a track center;    conducting a groove exposure with the groove exposure beam; and    conducting a phase pit exposure substantially simultaneously with the groove exposure,    wherein in a time of the phase pit exposure, a light amount of the groove exposure beam is reduced and a light amount of the phase pit exposure beam is smaller than the reduced light amount of the groove exposure beam.    
   
   
       8 . An original medium exposing method for producing the optical information recording medium of  claim 4 , said method comprising the steps of: 
 arranging a groove exposure beam at a track-center oriented position;    arranging a phase pit exposure beam at a place radially displaced from a track center;    conducting a groove exposure with the groove exposure beam; and    conducting a phase pit exposure substantially simultaneously with the groove exposure,    wherein in a time of the phase pit exposure, a light amount of the groove exposure beam is reduced and a light amount of the phase pit exposure beam is smaller than the reduced light amount of the groove exposure beam.    
   
   
       9 . An original medium exposing method for producing an optical information recording medium, said method comprising the steps of: 
 conducting a groove exposure for exposing an original medium with an exposure beam by arranging the groove exposure beam at a track-center oriented position; and    conducting a phase pit exposure for exposing the original medium with a phase pit exposure beam which is slightly displaced in a radial direction from the track-center oriented position,    wherein a light amount of the phase pit exposure beam is reduced from a light amount of the groove exposure beam,    wherein, in the optical information recording medium, grooves serve as information recording tracks and phase pits are formed as preformatted information on the tracks in a way such that radially opposite edge portions of the phase pits orthogonal to the tracks have tilt angles different from each other, and    wherein a center of the phase pits is radially displaced relative to a track center of the grooves, a gap width of the phase pits is greater than a gap width of the grooves such that each of the phase pits leaves a radial clearance from an immediately adjacent one of the grooves, and gap depths of the grooves and the phase pits are substantially identical.    
   
   
       10 . An exposure method for exposing a master for manufacturing an optical information recording medium, said method comprising the steps of: 
 exposing a light-sensitive layer of the master, to form on the light-sensitive layer a first latent image corresponding to a groove, by applying an exposure beam having constant light intensity and centered at a center of a track on the master; and    shifting the exposure beam in a radial direction from the center of the track, and exposing the light-sensitive layer with the shifted exposure beam, to form on the light-sensitive layer a second latent image corresponding to a phase pit.    
   
   
       11 . A stamper manufacturing method comprising: 
 forming a glass master including a light-sensitive layer;    exposing the glass master including the light-sensitive layer by applying the exposure method of  claim 10;     developing the light-sensitive layer to form a groove pattern on the glass master;    forming an electrically conductive film on a surface of the glass master having the groove pattern thereon;    applying an electroforming process to form a stamper plate on the conductive film; and    peeling the stamper plate from the glass master, and processing the stamper plate to form a stamper.    
   
   
       12 . A stamper formed by the stamper manufacturing method of  claim 11 .  
   
   
       13 . An optical information recording medium manufacturing method including the exposure method of  claim 10 .  
   
   
       14 . An optical information recording medium manufactured by the optical information recording medium manufacturing method of  claim 13 .  
   
   
       15 . An optical information recording medium master manufacturing apparatus comprising: 
 a laser light source; and    a laser control unit,    wherein said laser control unit controls said laser light source to apply an exposure beam to a master, in accordance with the exposure method of  claim 10 .    
   
   
       16 . A stamper manufacturing apparatus including the master manufacturing apparatus of  claim 15.