Fabrication of low-loss channel waveguides in Al_2O_3 and Y_2O_3 layers by inductively coupled plasma reactive ion etching

摘要

Etching of amorphous Al_2O_3 and polycrystalline Y_2O_3 films has been investigated using an inductively coupled reactive ion etch system. The etch behaviour has been studied by applying various common process gases and combinations of these gases, including CF_4/O_2, BCl_3, BCl_3/HBr, Cl_2, Cl_2/Ar and Ar. The observed etch rates of Al_2O_3 films were much higher than Y_2O_3 for all process gases except for Ar, indicating a much stronger chemical etching component for the Al_2O_3 layers. Based on analysis of the film etch rates and an investigation of the selectivity and patterning feasibility of possible mask materials, optimized optical channel-waveguide structures were fabricated in both materials. In Al_2O_3, channel waveguides were fabricated with BCl_3/HBr plasma and using a standard resist mask, while in Y_2O_3, channel waveguides were fabricated with Ar and using either a resist or a sputter deposited Al_2O_3 mask layer. The etched structures in both materials exhibit straight sidewalk with minimal roughness and sufficient etch depths (up to 530 nm for Al_2O_3 and 250 nm for Y_2O_3) for defining waveguides with strong optical confinement. Using the developed etch processes, low additional optical propagation losses (on the order of 0.1 dB/cm) were demonstrated in single-mode ridge waveguides in both Al_2O_3 and Y_2O_3 layers at 1550 nm.