SOI-based monolithic integration of SiON and Si planar optical circuits

In recent years there has been a growing interest in using Silicon on Insulator (SOI) as a platform for integrated planar optical circuits [] , this is mainly due to the high quality yield volume processes demonstrated by the CMOS manufacturing industry and recent MEMS technology progress[]. In this work we present monolithic integration of Silicon and SiON planar lightwave circuits on a single SOI chip processed in a CMOS fabrication environment. The demonstration of a processing scheme that yields low loss waveguides for both silicon and SiON as well as efficient transition of light between the two materials is the goal of this present work. The patterning of waveguides in both silicon and SiON regions is done in a self aligned process using one lithography mask and two separate dry etch steps each highly selective to one of the two materials. The effect of a high temperature anneal on the IR absorption of SiON related N-H bond was measured using FTIR and waveguide optical loss. Up to 98% reduction in absorption is demonstrated which allows acceptable loss across the C-band. We have achieved low propagation loss, single mode, and rib waveguides for both Silicon and SiON core regions as well as low loss silicon-SiON waveguides junction. The silicon-SiON junction loss has been measured to be 0.9+/-0.1dB, only 0.3dB greater than the theoretical value determined by Fresnel’s facet reflection. A new design of surface corrugated Bragg grating on the SiON section of the integrated device is described where the grating is embedded within the core which is composed of two slightly skewed index SiON layers. We show 8 times improvement of the grating spectral thermal stability compared to the previous work done on SOI platform. Achieving silicon-SiON monolithic integration of planar waveguide circuit enables future integration of already demonstrated applications, e.g., silicon can be used to achieve fast modulation, optical amplification, and Raman lasing whereas SiON can be used for a-thermal Bragg grating filters and efficient fiberwaveguide coupling.