Patent ID: 6423478
Filing Date: 2002-07-23
Classification: G11B

Abstract:
A method of forming a watermark image in a hybrid optical master disc for replication in a hybrid optical disc, comprising the steps of:a) providing a master substrate; b) coating a photoresist layer over a surface of the master substrate to form a photoresist layer having a thickness in a range from 290 to 350 nm; c) exposing at a laser beam groove exposure level a continuous spiral wobbled groove in the photoresist layer, the groove extending from a designated read-only memory (ROM) area to a designated recordable area of the master disc, and exposing at a laser beam depression exposure level depressions in the groove in the ROM area in response to data to be recorded therein; d) projecting a watermark image over at least portions of the ROM area and the recordable area at a watermark exposure level which is lower than the groove exposure level; and e) developing the photoresist layer to provide the continuous spiral wobbled groove, the depressions in the ROM area, and portions of the watermark image remaining in lands between successive turns of the spiral groove.