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

摘要

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 nonlinear 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.