Focused ion beam fabrication of photonic crystal structures

Abstract

Excess etch due to non-ideal beam profile during focussed ion beam etching of photonic crystal structures is investigated. It.has been found that a slow etch material mask improves the quality of etching. In recent years there has been increasing interest in photonic crystal (PhC) structures For light wave circuits. Currently most of this interest is in 2D structures as these are more suited to standard planar fabrication technologies. There has been much modeling of various types of PhC structures from square lattice to Penrose' type lattices. These structures have not been fully investigated experimentally, especially some OF the more interesting patterns, because of the limitations of current lithographic and pattern transfer processes. For example direct write E beam lithography is quite flexible, however it still requires pattern transfers through multiple mask layers before applying standard etching techniques (RIWICP). On the other hand, Focussed Ion Beam Etching (FIBE) requires no mask as the component is etched directly, which enables very Fast concept to test times. For PhC fabrication it is necessary to etch accurate and repeatable structures, and thus important to understand the limitations of the etch process and design the component with these in mind. One of these limitations is the excess etch due to the beam profile of the focused ion beam. Although the ion beam is focused to a small spot size, there is still a ne= Gaussian beam profile. For etching small structures this profile must he taken in to account.