Rapid fabrication of lightweight silicon-carbide mirrors

Silicon carbide (SiC) has long been recognized as an attractive mirror material due to its superior mechanical and thermal properties when compared to conventional optical materials. However, the material properties of SiC which make the material attractive from a design standpoint have often precluded its use when low cost and rapid delivery of an optical mirror were required. This paper describes an approach that was developed by Zygo Corporation, working in conjunction with POCO Graphite Inc. for the rapid fabrication of lightweight silicon carbide optics. This approach utilizes a SiC substrate produced by POCO Graphite Inc. using a non-traditional process coupled with deterministic finishing techniques developed by Zygo. Using this approach, we are now capable of producing high quality prototype components (λ/10 PV figure, 10 Å rms. micro roughness) of SiC within a few weeks, rather than the traditional period of months. Applications include lightweight scan mirrors, stage mirrors for lithography positioning tools, as well as similar applications where high stiffness and low weight are significant performance parameters. MRF polishing results comparing SiC to conventional optical materials are also presented.