Large Area High Quality, Electron Cyclotron Resonance Chemical Vapor Deposition SiC Thin Films for Astronomical Mirrors

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Silicon carbide is a leading new candidate for mirror blanks because of its high stiffness, relatively high thermal conductivity, and abrasion resistance. This base material contains pores or large grains, which make it difficult to provide a smooth front surface. A process has been developed for using electron cyclotron resonance chemical vapor deposition to deposit very smooth amorphous silicon carbide (SiC) on 100 mm substrates. This material is easily polished to obtain a 10-20A rms surface roughness. This process will be scaled up to coat large diameter optics. The main problems associated with scale up involved plasma gas dynamics and fluid flows. As part of this program, we will develop a general computational model that will be used for designing the gas delivery system. We will then modify an existing system to coat large-area optics with smooth, amorphous SiC.