RUGATE FILTERS GROWN BY PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

Rugate filters, based on the sinusoidal variation of the refractive index normal to the substrate, are fabricated by computer-controlled plasma-enhanced chemical vapor deposition (PECVD). Silane, nitrogen, and nitrous oxide are the source gases. The flow rate of nitrous oxide and the deposition time are controlled in real time to grow 10 and 20 periods of silicon oxynitride with a sinusoidally varying refractive index. The spectral responses of the rugate filters are in good agreement with theoretical calculations, demonstrating the reproducible growth of inhomogeneous dielectric layers by computer-controlled PECVD.