# US 5,705,246 A · Master disc for an optical disc and method for manufacturing the master disc > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,705,246 A - Document ID: US5705246A - Status: Granted - Kind: A - Application number: 08/546,948 - Filed: 1995-10-23 - Granted: 1998-01-06 - Earliest claimed: 1994-10-21 - Assignees: NEC Corporation - Inventors: Shinichi Katsuda - Web page: https://patentgrep.com/patent/US5705246A ## CPC - G11B 7/261: {Preparing a master, e.g. exposing photoresist, electroforming} - Y10S 428/913: Material designed to be responsive to temperature, light, moisture - Y10S 430/146: Laser beam - Y10T 428/21: Circular sheet or circular blank - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) - Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS - Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION ## Abstract 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. ## Claims ### Claim 1 An apparatus for manufacturing a stamper of an optical disc, comprising: a master disc, including a substrate having a main surface, and a photoresist laminate including a first photoresist layer formed on said main surface and a second photoresist layer formed on said first photoresist layer, said photoresist laminate having a first pit revealing said main surface of the substrate and a second pit revealing said first photoresist layer, said second photoresist layer having a photosensitivity higher than the photosensitivity of said first photoresist layer; and a scanning light source having a selectable beam intensity; wherein said scanning light source operates substantially at an ultra-violet wavelength. ### Claim 2 (depends on 1) An apparatus as defined in claim 1 wherein the photosensitivity of said second photoresist layer is approximately five times higher than the photosensitivity of said first photoresist layer. ### Claim 3 (depends on 1) An apparatus as defined in claim 1 wherein the photosensitivity of said second photoresist layer is approximately one order higher than the photosensitivity of said first photoresist layer. ### Claim 4 (depends on 1) An apparatus as defined in claim 1 wherein said second photoresist layer is made of g-line type photoresist and said first photoresist layer is made of i-line type photoresist. ### Claim 5 (depends on 1) An apparatus as defined in claim 1 wherein said selectable beam intensity includes a first intensity insufficient to expose said second photoresist layer, a second intensity high enough to expose said second photoresist layer but not high enough to expose said first layer, and a third intensity high enough to expose both the first and second photoresist layers. ### Claim 6 (depends on 1) An apparatus of claim 1 wherein said selectable beam intensity includes at least two steps in which the second step is five to ten times the intensity of the first step. ### Claim 7 An apparatus for manufacturing a stamper of an optical disc, including a substrate having a main surface; a photoresist laminate including at least two photoresist layers wherein a first photoresist layer is formed on said main surface and a second photoresist layer formed on said first photoresist layer, and any additional photoresist layers are formed on a preceding layer; said photoresist laminate having a plurality of pits, each having a depth corresponding to the number of exposed photoresist layers; each said photoresist layer having a photosensitivity higher than the photosensitivity of at least one preceding photoresist layer; and a light source having a selectable beam intensity; wherein said light source operates substantially at an ultraviolet wavelength. ### Claim 8 (depends on 7) An apparatus of claim 7 wherein said light source has a plurality of beam intensity settings corresponding to an exposure power necessary to fully expose one photoresist layer but not the next. ### Claim 9 (depends on 7) An apparatus of claim 7 wherein at least two of said photoresist layers are of an i-line type photoresist and a g-line type photoresist. ### Claim 10 A method for manufacturing a master disc for a stamper of an optical disc, said method including steps of: forming a photoresist laminate including a first photoresist layer and a second photoresist layer consecutively formed on a master disc substrate, 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 an intensity level from a set of preselected intensity levels of the scanning light source; and developing the photoresist laminate to form therein a first pit revealing the substrate and a second pit revealing the first photoresist layer; wherein said scanning light source operates substantially at an ultra-violet wavelength. ### Claim 11 (depends on 10) A method for manufacturing a master disc as defined in claim 10 wherein the photosensitivity of the second photoresist layer is approximately five times higher than the photosensitivity of the first photoresist layer. ### Claim 12 (depends on 10) A method for manufacturing a master disc as defined in claim 10 wherein the photosensitivity of the second photoresist layer is approximately one order higher than the photosensitivity of the first photoresist layer. ### Claim 13 (depends on 10) A method for manufacturing a master disc as defined in claim 10 wherein the second photoresist layer is made of g-line type photoresist and the first photoresist layer is made of i-line type photoresist. ### Claim 14 (depends on 10) A method as defined in claim 10 wherein said set of preselected intensity levels of said scanning light source includes at least three levels: a first intensity insufficient to expose said second photoresist layer, a second intensity high enough to expose said second photoresist layer but not high enough to expose said first layer, and a third intensity high enough to expose both the first and second photoresist layers. ### Claim 15 (depends on 10) A method as defined in claim 10 wherein at least one level in the set of preselected intensity levels is five to ten times the intensity of another level.