Hot-Wire CVD Hydrogenated Amorphous Silicon for Multi-layer Photonic Applications

Amorphous silicon (a-Si) is considered as one of the potential materials for multi-layer photonics due its high refractive index, linear and non-linear optical properties. This makes a-Si integration compatible with the Silicon-on-Insulator (SOl) photonics by increasing circuit density at each optical device layer. However, the high absorption loss of a-Si would require hydrogenation to passivate the dangling bonds for low loss optical waveguide interconnects and coupling of light between optical layers. Without an efficient passivation process, optical loss per layer would be too high for a viable multi-layer photonic platform. Therefore, we have developed a low temperature process hydrogenated a-Si (a-Si:H) with Hot-Wire Chemical Vapour Deposition (HWCVD) method that is compatible with back-end-of-the-line (BEOL) integration with active photonic or electronic layers. This work describes the experimental control of deposition temperature to achieve low loss a-Si:H waveguiding layer and the inter-layer waveguide coupling structures. Our latest results show a-Si:H deposited at 230 degrees C has the lowest propagation loss of 0.7 dB/cm for a sub-micron ridge waveguide at 1550 nm wavelength and 45 dB cross-talk isolation between two waveguides separated by 1 mu m of SiO2 layer.