Experimental Characterization of Roughness Induced Scattering Losses in PECVD SiC Waveguides

An atomic force microscope is used to directly measure the sidewall roughness of silicon carbide waveguides. In order to make the vertical walls accessible, the chip containing the rib waveguides was fixed on a 15 steel wedge and loaded onto an AFM scanner stage; this fitting ensures enough probe contact area on one of the sidewalls. The data was processed using a fully automated algorithm to extract the roughness in the direction of light propagation. This technique allows the investigation of devices at chip level without damaging the structures. The method was calibrated using a well-known smoothing process based on thermal oxidation of silicon waveguides to achieve low transmission loss and applied to PECVD silicon carbide waveguides. A very low loss behavior at 1.3 m ( dB/cm) is reported.