Improvement of Sidewall Roughness of Submicron SOI Waveguides by Hydrogen Plasma and Annealing

We report the successful fabrication of low-loss submicrometric silicon-on-insulator strip waveguides for on-chip links. Postlithography treatment and postetching hydrogen annealing have been used to smoothen the waveguide sidewalls, as roughness is the major source of transmission losses. An extremely low silicon line-edge roughness of 0.75 nm is obtained with the optimized process flow. As a result, record-low optical losses of less than 0.5 dB/cm are measured at 1310 nm for strip waveguide dimensions exceeding 500 nm. They range from 1.2 to 0.8 dB/cm for 300-400-nm-wide waveguides. Those results are to our knowledge the best ever published for a 1310-nm wavelength. These results are compared to modeling based on Payne and Lacey equations.