Reactive Ion Etching of X-Cut LiNbO₃ in an ICP/TCP System for the Fabrication of an Optical Ridge Waveguide

Abstract

In this study, the technology for producing ridge waveguides with a minimal roughness of the sidewalls and material surface in a near-waveguide region was developed with the purpose of fabricating miniature photonic integrated circuits on a LiNbO3 substrate. Plasma etching processes were used for the ridge waveguide fabrication on different material substrates. The specifications of the equipment and plasma source, method of mask fabrication and substrate material determined the process conditions for producing ridge waveguides with minimal sidewall roughness. In this work, for the ridge waveguide fabrication, the processes of reactive ion etching of LiNbO3 with a chromium mask were carried out in a mixture of SF6/Ar with an ICP/TCP plasma source. The process of plasma etching the LiNbO3 with the ICP/TCP plasma source is not well studied, especially for integrated photonics purposes. As a result of our experimental work, the narrow ranges of technological parameters suitable for producing ridge waveguides on LiNbO3 with smooth sidewalls, a slope angle of 60°–75° and a minimal quantity of observed defects in the near-waveguide region were identified. A model explaining the kinetics of the etching process of LiNbO3 in SF6/Ar plasma as a physical–chemical process was proposed.

Keywords

• lithium niobate
• ridge waveguides
• reactive ion etching