Atomic layer deposited etch stop layers for hydrofluoric acid

Abstract

We report on the evaluation of the etch rate in hydrofluoric acid (HF) for various atomic layer deposited (ALD) thin films. Specifically, the intent is to characterize several films as potential etch stop layers as HF is often used as a release etch for various sacrificial films but most commonly SiO2. Traditionally in MEMS, SiN has been used as an HF etch stop, and we show that plasma enhanced ALD (PEALD) of SiN at 350C can achieve similar etch rates to SiN from low pressure chemical vapor deposition (LPCVD) at 850C. Further, the etch rate of PEALD SiN is drastically reduced when the film contains ~10% AlN as a dopant. Additionally, several metal oxide films are evaluated for their etch characteristics as deposited and as a function of post-deposition anneal temperature. Some of the evaluated metal oxide films showed greater HF etch resistance than PEALD SiN after anneals of moderate temperature (~400C).