Reduction of sidewall roughness in silicon-on-insulator rib waveguides

Silicon-on-insulator (SOI) rib waveguides with residual sidewall roughness were achieved through inductive coupled plasma reactive ion etching (ICPRIE) process. Sidewall roughness is the dominant scattering loss source. Conventional ICPRIE could result in the sidewall ripples derived from the etch/deposition cycle steps. Mixed ICPRIE process and hydrogen annealing were used to improve the sidewall roughness of SOI rib waveguides and eliminate the sidewall ripples. Scan electron microscope and atomic force microscope were used to demonstrate the surface profiles of the sidewall. The results indicated that the sidewall roughness could be low down to 0.3 nm level by optimization and combination of these two techniques and the ripples disappeared. According to the scattering theory developed by Payne and Lacey, the scattering loss could be reduced to below 0.01 dB/cm.