InP-based Waveguides: comparison of ECR Plasma Etching and Wet-chemical Etching

Electron Cyclotron Resonance (ECR) reactive ion etching of InP-based waveguide structures was studied using CH4/H2/Ar chemistry. The ECR process was first optimized on InP substrates before being used to process waveguides. Stripes of 2 µm width were patterned in silicon nitride and used as masking to etch strip-loaded waveguides. These waveguides were compared with wet-etched waveguides, in order to identify the dominant loss mechanism. Fabry-Perot loss measurements showed values as low as 1.1 dB/cm for the ECR-etched waveguides. From the comparison it appears that roughness of the sidewalls is more important than surface damage for the loss of these waveguides