ICP polishing of silicon for high quality optical resonators on a chip

TL;DR

This paper demonstrates that ICP polishing significantly improves the surface quality of silicon micro-mirrors used in on-chip optical resonators, achieving ultra-smooth surfaces that enhance cavity finesse.

Contribution

It introduces a method to enhance silicon mirror surfaces via ICP polishing, improving shape and roughness for high-quality on-chip optical resonators.

Findings

Surface roughness reduced to 0.5 nm after coating

Achieved surface roughness of 1 nm before coating

Optical cavity finesse limited by mirror shape

Abstract

Miniature concave hollows, made by wet etching silicon through a circular mask, can be used as mirror substrates for building optical micro-cavities on a chip. In this paper we investigate how ICP polishing improves both shape and roughness of the mirror substrates. We characterise the evolution of the surfaces during the ICP polishing using white-light optical profilometry and atomic force microscopy. A surface roughness of 1 nm is reached, which reduces to 0.5 nm after coating with a high reflectivity dielectric. With such smooth mirrors, the optical cavity finesse is now limited by the shape of the underlying mirror.