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Master disc for an optical disc and method for manufacturing the master disc
| Details |
Inventors: Katsuda, Shinichi;
Assignee: NEC Corporation (Tokyo, JP)
Primary Examiner: Evans; Elizabeth
Assistant Examiner:
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas, PLLC
An exposure master disc includes a photoresist laminate formed on a glass substrate. The photoresist laminate includes an i-line type, first photoresist layer and a g-line type, second photoresist layer consecutively formed on the substrate. The photoresist laminate is exposed by a scanning laser light while selecting the exposure power level, to thereby effectively expose the first and second photoresist layers or to effectively expose only the second photoresist layer. The resultant photoresist laminate has first pits revealing the substrate and second pits revealing the first photoresist layer, thereby forming two types of pits having different depths. Two type of pits and flat surface of the photoresist laminate provide three-valued data for a higher storage density. |
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DETAILED DESCRIPTION In view of the foregoing, it is an object of the present invention to provide a master disc and a method for manufacturing the master disc in which a plurality of pits having different depths can be accurately formed in a simplified manner.
A master disc for use in manufacturing a stamper of an optical disc according to the present invention comprises a substrate having a substantially flat surface, a photoresist laminate including a first photoresist layer formed on the flat surface and a second photoresist layer formed on the first photoresist layer, the photoresist laminate having a first pit revealing the flat surface of the substrate and a second pit revealing the first photoresist layer, the second photoresist layer having a photosensitivity higher than the photosensitivity of the first photoresist layer.
A method for manufacturing a master disc for use in manufacturing a stamper of an optical disc includes the steps of: forming on a substrate a photoresist laminate including a lower, first photoresist layer and an upper, second photoresist layer, the second photoresist layer having a photosensitivity higher than the photosensitivity of the first photoresist layer; exposing, by a scanning light source, the photoresist laminate while selecting laser power level of the scanning laser light: and developing the photoresist laminate to form a first pit revealing the substrate and a second pit revealing the first photoresist layer.
In accordance with the present invention, when the scanning exposure power is properly selected during scanning exposure, the exposure can be performed such that the upper, second photoresist layer is effectively exposed while the underlying, first photoresist layer is not effectively exposed.
Accordingly, a plurality of pits having different depths can be simply and accurately formed by a single exposure process.
This makes it feasible to manufacture high storage density optical discs at reduced costs.
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Manufacturing Materials 
