Advances in Tensile Testing of Polysilicon Thin Films

Abstract

Polysilicon is the most widely used material in current commercial MEMS products, yet its mechanical properties are not fully determined. Vapor deposited polysilicon is thin — on the order of a few microns — which makes handling and testing difficult. It is desirable to use mechanical tests similar to those standardized by ASTM, but this requires special techniques and procedures. Tensile tests of 3.5 micron thick polysilicon film have been conducted and these are briefly described. Two advances in mechanical property testing are then presented. A preliminary investigation of the effect of hydrofluoric acid on the tensile properties of polysilicon shows no deleterious effect of this acid which is commonly used as a release agent. Fracture toughness testing of polysilicon, in which crack opening displacement is measured (an approach similar to that specified by ASTM), yields a preliminary value of 1.6 MPa-m1/2.