Redeposition-free inductively-coupled plasma etching of lithium niobate for integrated photonics.

Lithium niobate on insulator is being established as a versatile platform for a new generation of photonic integrated devices. Extensive progress has been made in recent years to improve the fabrication of integrated optical circuits from a research platform towards wafer-scale fabrication in commercial foundries, and optical losses have reached remarkably low values approaching material limits. In this context, argon etching of lithium niobate waveguides has been shown to provide the best optical quality, yet the process is still challenging to optimise due to its physical nature. Namely, the micro-masking effects introduced by the material redeposition and a close to one etch mask selectivity for deep etches. We present a workflow to identify the parameter set offering the best etching results independent of the plasma system being used. We show how to reach the redeposition-free regime and propose three methods to achieve redeposition-free lithium niobate etching with good quality sidewalls without need of wet chemistry for cleaning.