Abstract

Read only Compact Discs (CDs), such as the CD-ROM and Digital Audio CD, are made by concurrently forming the plastic disc and the spiral track of pits that represent the data carried on the surface of the disc via an injection molding operation, and subsequently applying a reflective metal layer in a vacuum coating step and a protective polymer layer via spin coating. The original data that is replicated on these "pressed" CDs is carefully written on a master disc (that is used to form the injection molding tool) using a precision master laser writer that is housed in a very clean environment. On the other hand, writable CDs, such as the CD-R and PhotoCD, are made by first using injection molding to form a plastic disc that has a continuous spiral (tracking) groove on one surface and then sequentially coating that grooved surface with a vacuum deposited dielectric layer, a spin coated organic "pit-forming" layer, a vacuum coated metal reflector layer and a spin coated organic protective layer. Although the spiral tracking groove that is replicated on the surface of the writable CD's molded plastic substrate is initially written on a master disc using essentially the same precision laser writer that was used to create the pressed CDs' master discs, the marks that correspond to the user digital data carried by the writable CD are written one at a time via an optical CD disc drive that is housed in an ordinary environment.

© 1994 Optical Society of America