SOI planar photonic crystal fabrication: Etching through SiO2/Si/SiO2 layer systems using fluorocarbon plasmas

Dry plasma etching of sub-micron structures in a SiO2/Si/SiO2 layer system using Cr as a mask was performed in a fluorocarbon plasma. It was determined that the best anisotropy could be achieved in the most electropositive plasma. A gas composition yielding the desired SOI planar photonic crystal structures was optimized from the available process gases, Ar, He, O2, SF6, CF4, c-C4F8, CHF3, using DC bias data sets. Application of the c-C4F8/(noble gas) chemistry allowed fabrication of the desired SOI planar photonic crystal. The average etching rates for the pores and ridge waveguide regions were about 71 and 97 nm/min, respectively, while the average SiO2/Si/SiO2 to Cr etching selectivity for the ridge waveguide region was about 33:1 in case of the c-C4F8/90%Ar plasma with optimized parameters.