Stamper, mold system, recording medium substrate, recording medium, optical disc substrate, optical disc, and method for producing stamper

Abstract

A stamper for forming a data recording region on a recording medium substrate by means of a transfer surface thereof. The transfer surface transfers a predetermined set of data to the recording medium substrate. The stamper is fitted on at least one of metal molds that are arranged opposite one another for forming the recording medium substrate. The stamper includes a stepped portion formed as bends in the material of the stamper. The stepped portion is configured to project from the transfer surface toward the recording medium substrate.

1 . A stamper for forming at least a data recording region on a recording medium substrate by means of a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, the stamper fitted on at least one of metal molds arranged opposite one another for forming the recording medium substrate, wherein 
 a stepped portion formed as bends in the material of the stamper, and    the stepped portion is configured to project from the transfer surface toward the recording medium substrate.    
   
   
       2 . The stamper according to  claim 1 , wherein the stepped portion is formed to have a circular shape and the circle is sized so that an end surface of the stepped portion engages an edge of an inner peripheral wall of the mold, the inner peripheral wall forming an outer peripheral surface of the recording medium substrate.  
   
   
       3 . The stamper according to  claim 2 , wherein the end surface of the stepped portion is bent on either radial end thereof so that the stepped portion has a radial cross-section that projects toward the recording medium substrate.  
   
   
       4 . A recording medium substrate made by using a mold system, the mold system including: 
 a ring mold having an inner peripheral wall for forming an outer peripheral surface of a recording medium substrate;    a pair of planar molds arranged opposite one another for forming top and bottom surfaces of the recording medium substrate;    a stamper fitted on at least one of the pair of planar molds, the stamper forming a data recording region on the recording medium substrate through a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, wherein    the stamper is provided with a stepped portion formed as bends in a material of the stamper, the stepped portion being configured to project from the transfer surface toward the recording medium substrate.    
   
   
       5 . The recording medium substrate according to  claim 4 , wherein the recording medium substrate has a circumferential recess formed radially outside the data recording region on at least one of the surfaces of the recording medium substrate, the recess formed by the stepped portion of the stamper in the mold system.  
   
   
       6 . The recording medium substrate according to  claim 5 , wherein a radially outermost edge of the recess on one of the surfaces is lower than a radially innermost edge of the recess as viewed along the thickness of the recording medium substrate.  
   
   
       7 . The recording medium substrate according to any one of  claim 5 , wherein the radially outermost edge of the recess on one of the surfaces is lower than the radially innermost edge of the recess and is higher than a deepest point of the recess as viewed in the thickness of the recording medium substrate.  
   
   
       8 . The recording medium substrate according to  claim 6 , wherein the radially outermost edge of the recess on one of the surfaces is lower than the radially innermost edge of the recess and is higher than a deepest point of the recess as viewed in the thickness of the recording medium substrate.  
   
   
       9 . The recording medium substrate according to  claim 5 , wherein the recess has a depth that gradually decreases as it extends radially outward from the deepest point, the recess substantially smoothly continues to a peripheral region thereof so that the peripheral region has saw-tooth shape in its radial cross-section.  
   
   
       10 . The recording medium substrate according to  claim 6 , wherein the recess has a depth that gradually decreases as it extends radially outward from the deepest point, the recess substantially smoothly continues to a peripheral region thereof so that the peripheral region has saw-tooth shape in its radial cross-section.  
   
   
       11 . The recording medium substrate according to  claim 7 , wherein the recess has a depth that gradually decreases as it extends radially outward from the deepest point, the recess substantially smoothly continues to a peripheral region thereof so that the peripheral region has saw-tooth shape in its radial cross-section.  
   
   
       12 . The recording medium substrate according to  claim 5 , wherein the radially innermost edge of the recess is positioned at a distance of 0.965d from the center of the substrate or further, preferably 0.975d or further, and more preferably 0.983d or further, assuming d is the radius of the outermost circumference of the substrate.  
   
   
       13 . The recording medium substrate according to  claim 6 , wherein the radially innermost edge of the recess is positioned at a distance of 0.965d from the center of the substrate or further, preferably 0.975d or further, and more preferably 0.983d or further, assuming d is the radius of the outermost circumference of the substrate.  
   
   
       14 . The recording medium substrate according to  claim 7 , wherein the radially innermost edge of the recess is positioned at a distance of 0.965d from the center of the substrate or further, preferably 0.975d or further, and more preferably 0.983d or further, assuming d is the radius of the outermost circumference of the substrate.  
   
   
       15 . The recording medium substrate according to  claim 9 , wherein the radially innermost edge of the recess is positioned at a distance of 0.965d from the center of the substrate or further, preferably 0.975d or further, and more preferably 0.983d or further, assuming d is the radius of the outermost circumference of the substrate.  
   
   
       16 . A recording medium including a recording medium substrate and a light-transmitting layer disposed on at least one of surfaces of the recording medium substrate, wherein 
 the recording medium substrate is made by using a mold system, the mold system including:    a ring mold having an inner peripheral wall for forming an outer peripheral surface of a recording medium substrate;    a pair of planar molds arranged opposite one another for forming top and bottom surfaces of the recording medium substrate;    a stamper fitted on at least one of the pair of planar molds, the stamper forming a data recording region on the recording medium substrate through a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, wherein    the stamper includes a stepped portion formed as bends in a material of the stamper, the stepped portion being configured to project from the transfer surface toward the recording medium substrate.    
   
   
       17 . A method for producing a stamper using a stamper production disc having a negative pattern region that includes microscopic projections/recesses that are a negative image of a data pattern to be formed on a recording medium substrate, the stamper being fitted on at least one of metal molds that are arranged opposite one another for forming the recording medium substrate, the stamper forming a data recording region on the recording medium substrate through a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, the method comprising the steps of: 
 forming on the stamper production disc a circumferential recess for forming a stepped portion, the recess having a larger depth and a larger width than the microscopic projections/recesses; and    forming the stamper by using the stamper production disc, the stamper having the circumferential stepped portion that is formed by bending a material of the stamper by means of the recess, the stamper having a transfer surface transferred from the negative pattern region.    
   
   
       18 . A method for producing a stamper using a master disc and a mother disc, the stamper being fitted on at least one of metal molds that are arranged opposite one another for forming a recording medium substrate, the stamper forming a data recording region on the recording medium substrate through a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, the method comprising the steps of: 
 forming the master disc having a negative pattern region that is a negative image of a data pattern to be formed on the recording medium substrate;    forming the mother disc using the master disc, the mother disc having a positive pattern region transferred from the negative pattern region;    forming on the mother disc in the vicinity of the positive pattern region a recess for forming a stepped portion, the recess having a larger depth and a larger width than microscopic projections/recesses of the positive pattern region; and    forming the stamper using the mother disc, the stamper having the stepped portion formed by the recess as bends in a material of the stamper, the stamper having the transfer surface transferred from the positive pattern region.    
   
   
       19 . A method for producing a stamper using a master disc and a mother disc, the stamper being fitted on at least one of metal molds that are arranged opposite one another for forming a recording medium substrate, the stamper forming a data recording region on the recording medium substrate through a transfer surface thereof, the transfer surface transferring a predetermined set of data to the recording medium substrate, the method comprising the steps of: 
 forming the master disc having a positive pattern region that substantially matches a data pattern to be formed on the recording medium substrate;    forming a first mother disc using the master disc, the first mother disc having a negative pattern region transferred from the positive pattern region;    forming a second mother disc using the first mother disc, the second mother disc having a second positive pattern region transferred from the negative pattern region;    forming a recess for forming a stepped portion either on the master disc in the vicinity of the positive pattern region or on the second mother disc in the vicinity of the second positive pattern region, the recess having a larger depth and a larger width than microscopic projections/recesses of the patterns; and    forming the stamper using the master disc or the second mother disc, the stamper having the stepped portion formed by the recess as bends in a material of the stamper, the stamper having the transfer surface transferred from the positive patter region or the second positive pattern region.