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Silicon nitride is widely used in photonic integrated circuits process flow, it’s an important component of the integrated silicon-based optical device. The fabrication of a low-loss waveguide is important in silicon nitride microresonator, which is generally composed of silica cladding and silicon nitride waveguide. This paper mainly optimizes the process flow of silicon nitride and silicon oxide film to obtain a low-loss waveguide. A critical thickness of the light leakage from the silicon nitride waveguide to the silicon substrate is obtained by simulation, and the process flow of dry oxidation, wet oxidation, and annealing are combined to fabricate silica film with high uniformity, compactness, and confinement. This process flow traps the light leakage from silica to silicon and reduces the surface roughness, providing a good environment for the growth of silicon nitride. Thin silicon nitride film is fabricated after the thick silicon nitride film is grown by two-step process flow, a long-time annealing after growing the thin film greatly reduced the loss of waveguide. In this paper, the scattering loss is reduced by optimizing the process flow of the silica layer, and the fabrication optimization of the silicon nitride layer leads to low absorption loss, providing superior performance optimization for high Q silicon nitride microresonators of photonic integrated circuits.
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