Membranes of SiO xN y with 3D topography formed by PECVD for MEMS applications

Abstract

Self-sustained corrugated membranes with 3D topography are fabricated utilizing low stress silicon oxynitride (SiO x N y ) films obtained by the PECVD technique at low temperatures. The membranes are 4 μm thick and exhibit a pronounced 3D profile that defines pyramids and truncated pyramids of ∼70 μm high and with 100, 200 and 400 μm in the base. The SiO x N y films have been obtained at 320 °C, from gaseous mixtures of SiH 4 and N 2O. The deposition conditions of the films were established in previous works and were selected to obtain high deposition rates, low total internal mechanical stress and high resistance to chemical corrosion in KOH solutions. The microstructures are fabricated as an array of four large area membranes, with pyramidal microstructures of different size. The membranes are fabricated by bulk micromachining of the silicon substrates and the pyramidal microstructures were investigated mainly by optical and scanning electron microscopy. The results confirm the excellent mechanical stability of the SiO x N y films and their resistance to KOH corrosion, which allow the fabrication of self-sustained membranes with up to ∼1 cm 2 of total area, only possible due to the low internal stress of the films.