Master disk and method of manufacturing the same

Abstract

There are provided an optical disk and a manufacturing method thereof which can increase its recording capacity, e.g. to 15 GB or higher. This optical disk may comprises an optical disk substrate 3 in which successive pits corresponding to a recording signal are formed, a reflection film 4 formed in this optical disk substrate 3 on its surface that successive pits 2 are formed and a light transmissive layer 5 formed on this reflection film 4. When a recorded signal is read out, i.e. reproduced from the optical disk, a signal recorded as successive pits is read out by irradiating of short-wavelength laser light having a wavelength of 350 nm to 420 nm from the side of the light transmissive layer 5 formed on the surface of the optical disk. Moreover, in this optical disk, when the successive pits are observed from the side of the light transmissive layer irradiated by reproducing laser light, the successive pits contain pits having length and width ranging from 80 nm to 250 nm, and the reflection film has the film thickness selected to be 20 nm or less, e.g. greater than 8 nm.

1 . An optical disk comprising an optical disk substrate in which successive pits corresponding to a recording signal are formed, a reflection film formed in said optical disk substrate on its surface that said successive pits are formed and a light transmissive layer formed on said reflection film, wherein a signal recorded as said successive pits is read out by irradiating of laser light having a wavelength ranging from 350 nm to 420 nm, characterized in that when the successive pits are observed from the side of said light transmissive layer, said successive pits contain pits having length and width ranging from 80 nm to 250 nm and said reflection film has a film thickness selected to be 20 nm or less.  
     
     
         2 . An optical disk as claimed in  claim 1 , comprising a signal recording film such as a phase-change film between the reflection film and the light transmissive layer.  
     
     
         3 . An optical disk as claimed in  claim 2 , wherein the reflection film and/or signal recording film is formed as two or more layers.  
     
     
         4 . An optical disk as claimed in  claim 1 , wherein said reflection film is made of one or more kinds of materials of aluminum, silver and gold or two or more kinds of alloy materials thereof.  
     
     
         5 . An optical disk as claimed in  claim 2 , wherein said reflection film is made of one or more kinds of materials of aluminum, silver and gold or two or more kinds of alloy materials thereof.  
     
     
         6 . An optical disk as claimed in  claim 3 , wherein said reflection film is made of one or more kinds of materials of aluminum, silver and gold or two or more kinds of alloy materials thereof.  
     
     
         7 . An optical disk as claimed in  claim 1 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         8 . An optical disk as claimed in  claim 2 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         9 . An optical disk as claimed in  claim 3 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         10 . An optical disk as claimed in  claim 4 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         11 . An optical disk as claimed in  claim 5 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         12 . An optical disk as claimed in  claim 6 , wherein said reflection film has a reflectance selected to be 15% or greater.  
     
     
         13 . An optical disk manufacturing method comprising the steps of: 
 producing an optical disk manufacturing master disk for forming successive pits by exposure corresponding to a recording signal using laser light having a wavelength ranging from 200 nm to 370 nm;    producing an optical disk substrate in which successive pits containing pits having length and width both ranging from 80 nm to 250 nm are formed by transferring said successive pits of said master disk; and    forming a reflection film having a film thickness of 20 nm or less in said optical disk substrate on its surface that said successive pits are formed.    
     
     
         14 . An optical disk manufacturing method as claimed in  claim 13 , wherein said reflection film is made of one or more kinds of materials of aluminum, silver and gold or alloy materials containing these materials.  
     
     
         15 . An optical disk manufacturing method as claimed in  claim 13 , wherein said reflection film has a reflectance selected to be 15% or greater.