Ridge structure etching of LiNbO₃ crystal for optical waveguide applications

A plasma dry etching technique has been applied to the fabrication of LiNbO₃ optical waveguide with a ridge structure for broadband operation. The etching characteristics of a LiNbO₃ single crystal have been investigated according to various ratios of Ar/C₃F ₈ gas mixture. A Ni metal was used as a dry etching mask. The effects of a gas mixture ratio on etching profile angle, sidewall roughness and etching rate were also studied. The etching surface roughness was evaluated by atomic force microscopy (AFM). The etch rate and profile was observed by scanning electron microscopy (SEM). The optimum etching conditions, considering etch rate, profile and surface roughness, were obtained at the 20 sccm C ₃F₈ gas flow.