Abstract

Optical thin films generated by the co-deposition of two or more materials exhibit a refractive index proportional to the indices of the components in proportion to the mixing ratio. The coevaporation of Ti₂O₃ and SiO requires strict control of rates and chamber environmental parameters to maintain proper stoichiometry and film performance. Films are oxidized to TiO₂ and SiO₂ at the substrate. A broad-band photometer monitors film development in the visible region. Photometer scans are acquired by the control computer every 10 seconds. Film absorption, index, and optical thickness are found to be sensitive to rate as well as trace amounts of water vapor. Absorption is due to unconverted SiO, and although the film will convert on chamber venting or a post bake, absorption inhibits reliable interpretation of photometer results. Reliable results are achieved by using a rule-based computer algorithm during source ramp-up and rate stabilization to verify system readiness. Environmental parameters are compared to a data base of previous runs to verify normal status. Photometer scans and scan-to-scan differences are checked for normal behavior. Computer rules are performance goal-oriented, and system status is weighed against the desired film spectral performance.

© 1990 Optical Society of America