An ALD etch-back method to fabricate high aspect ratio nanopillar arrays for photonic crystal sensors

Abstract

An IC-compatible technique for photonic crystal sensors is presented here to fabricate dense arrays of high aspect ratios nanopillars, which are made of extremely hard materials that are difficult to shape, such as TiO2. This technique, called Atomic layer deposition ARrays Defined by Etch-back technique (AARDE), can significantly reduce direct bombardment on the functional surfaces and allows the precise control of the size of the densely spaced high pillars. A case study of an array of 1 μm pitch and 1.7 μm high TiO2 pillars is investigated. Starting from 145 nm radius Si rods, the pillars are coated with a 78 nm thick ALD TiO2 layer and subsequently uncapped by a short time plasma etching. The exposed Si cores are then removed and a second ALD deposition is used to refill the opened holes and extend the pillar radius to the desired value.