Changes in surface stress, morphology and chemical composition of silica and silicon nitride surfaces during the etching by gaseous HF acid

Abstract

HF acid attack of SiO 2 and Si 3N 4 substrates is analyzed to improve the sensitivity of a sensor based on microcantilever. Ex situ analysis of the etching using XPS, SIMS and AFM show significant changes in the anisotropy and the rate of the etching of the oxides on SiO 2 and Si 3N 4 surface. Those differences influence the kinetic evolution of the plastic bending deflection of the cantilever coated with SiO 2 and Si 3N 4 layer, respectively. The linear dependence between the HF concentration and the Si 3N 4 cantilever bending corresponds to a deep attack of the layer whereas the non-linear behavior observed for SiO 2 layer can be explained by a combination of deep and lateral etching. The cantilever bending is discussed in terms of free surface energy, layer thickness and grain size.