Apparent and steady-state etch rates in thin film etching and under-etching of microstructures: II. Characterization

Abstract

The apparent and steady-state etch rates of PECVD SiO2, HDP SiO2 and PECVD Si3N4 are measured both in a single thin film and a stacked film configuration. This is done for a HF:H2O/1:1, a HF49 wt%: IPA/1:1 and a BHF solution. It is shown that etch rates vary with the used etch time, confirming the influence of both an incubation and a rinsing period on the average etch rate when performing typical ex situ etch rate experiments. Hence, this second part of a set of two papers provides the experimental evidence for part I where a general etch rate model was proposed. Furthermore this work shows that the etch rate varies whether it is determined on a single layer, in a stacked configuration or while under-etching a structural layer. This confirms the need of a straightforward characterization method for under-etching measurements at the sacrificial release stage of MEMS fabrication processes. Therefore, a new characterization method, using a suspended beam array and a surface profilometer, is proposed to determine the amount of under-etch after sacrificial release of surface micromachined devices.