Silicon nitride films on silicon for optical waveguides

Abstract

Silicon nitride (Si₃N₄) thin film optical waveguides with propagation losses of less than 0.1 dB/cm for the TE₀ mode at λ₀ = 6328 Å have been successfully grown by low-pressure chemical vapor deposition. Silicon wafers 5 cm in diameter were used as substrates, and the Si₃N₄ was separated from the substrate by a steam-oxide SiO₂ buffer layer. Propagation losses are examined for the various waveguide modes, and their dependence on waveguide parameters and wavelength are discussed and compared with exact calculations. Leakage into the silicon substrate is shown to be a major loss mechanism, especially at longer wavelengths and for higher mode numbers.