Ammonium Fluoride Anti-stiction Treatments For Polysilicon Microstructures

Abstract

A surface treatment for stiction reduction is described which has been shown to passivate surface micromachined micromechanical structures. Surface passivation is accomplished during the etching of silicon by ammonium fluoride (NH/sub 4/F) by means of a high quality hydrogen-termination of surface dangling bonds. The NH/sub 4/F treatment is integrated directly with the conventional release process, and is compatible with super critical drying techniques. Use of a cantilever beam array specifically designed for the measurement of in-use stiction showed a decrease in the work of adhesion from 42 mJ/m/sup 2/ for the hydrophilic release to less than, 0.3 mJ/m/sup 2/ for the NH/sub 4/F release processes. Encapsulation in a dry ambient will be necessary, as the hydrogen-terminated surface oxidizes after about one week in room air.