Fabrication of low-loss silicon nanophotonic waveguide for photonic device integration

As the basic building block for photonic device integration, silicon nanophotonic waveguide requires low-loss propagation for high-performance ultra-compact photonic device. We experimentally study SiO₂ grown by two different methods (thermal oxidation and PECVD) as hard masks for Si nano-waveguides fabrication and study their effects on propagation loss. It was found that the denser and smoother quality of thermally grown SiO₂ will increase the etch selectivity of Si and reduce the line-edge roughness transferred to the Si nanowaveguide sidewall, hence giving a lower loss compared to having PECVD SiO₂ hard mask. With thermally grown SiO₂ as hard mask, the Si nano-waveguides loss can have a loss reduction as high as 5.5 times for a 650 nm wide nanowaveguide. Using thermally grown SiO₂ as hard mask will allow the Si nano-waveguide to have as low a propagation loss as direct resist mask and enable III-V semiconductor on silicon via bonding for multifunctional photonic system on chip.