Novel Polymeric Protective Coatings for Hydrofluoric Acid Vapor Etching during MEMS Release Etch

Abstract

Micro-electro-mechanical system (MEMS) is rapidly becoming a critical part of advanced fabrication technology such as cellular phones, micromirrors, radio frequency (RF) devices, microprobes, and pressure sensors. Release etching of a sacrificial layer of silicon oxide plays an important role in creating the moving parts during these MEMS device fabrication. Traditionally, wet fluorinated etchants have been applied in order to achieve release etching, by which liquid surface tension can cause the MEMS microstructures to stick together (“stiction”) upon removing from aqueous bath or during the drying of released wet-etched structure. It has been demonstrated that using a hydrofluoric acid (HF) vapor release etch can efficiently circumvent stiction phenomena owing to the fact that it substantially eliminates the surface tension that causes the stiction. Conventionally, inorganic based films such as silicon nitride, alumina, SiC, polysilicon, amorphous silicon, and aluminum etc were used as vapor HF etch-resistant mask materials, which require very high temperature and vacuum deposition techniques often lengthy, complicated and costly. Herein, a novel spin-on and polymeric blanket HF-resistant coating material is presented to provide protection of both silicon oxide and aluminum against HF attack during vapor HF etching. Our newly developed polymeric coatings can be processed at lower temperature (<250 °C) and thinner films (less than 10μm) for extended vapor HF etching period (longer than 1 hour). Hence, our vapor HF resistant materials will enable the MEMS industry to significantly lower the cost of manufacturing MEMS devices and will significantly simplify the manufacturing process as well.