Influence of interface structure on chemical etching process for air gap of microelectromechanical system based on surface micromachining

This paper analyses the problems posed by the interface structure during ch emical etching by Hydro-fluoric (HF) acid for creating air gaps in microele ctromechanical system (MEMS) devices using PZT(53/47) films and surface mic romachining techniques. In order to investigate the influence of interface structure on the HF chemical etching process. Pt/PZT/Pt/Ti/TiO2/polysilicon /Si3N4/PSG/Si (Samples A and C) and Pt/PZT/RuO2/Ru/Si3N4/PSG/Si (Sample B) structures were fabricated. These structures are selected for a microcantil ever beam and/or an uncooled TR detectors fabricated; with PZT piezoelectri c/pyroelectric films based on the surface micromachining technique. Both ne ed etching for the removal of phosphor silicate glass (PSG) to create an ai r gap. If the devices had a poor interface structure, they would fail durin g the HF chemical etching process because the poor interface structure woul d act as a kind of penetration path for etching acid leading to unwanted et ching. Therefore, it is very important to investigate the interface structu re to fabricate efficient MEMS devices. In this study two different solutio ns have been suggested to improve the interface structure. The first is pos t thermal annealing at 900 degrees C for 30 min. after deposition of polycr ystalline silicon for sample A. Secondly, a RuO2/Ru hybrid electrode was de posited on Si3N4 directly instead of on the Pt/Ti/TiO2/Polysilicon electrod e, which has Pt/PZT/RuO2/Ru/Si3N4/PSG/Si as the device structure. These two solutions suggest that a dense interface structure increases enhances of s uccess of the chemical etching process of MEMS devices fabricated using PZT films and surface micromachining techniques.