A GEOMETRICALLY NONLINEAR MODEL FOR PREDICTING THE INTRINSIC FILM STRESS BY THE BENDING-PLATE METHOD

This study presents a new method for calculating the intrinsic stress that develops in a film as it is deposited onto a substrate. Previous investigations have employed a simplified, geometrically linear beam or plate theory that assumes very thin films and, in most cases, a uniform film stress in order to calculate the film stress from measured deflections of the substrate. The model presented here makes no assumptions regarding the thickness of the film or the uniformity of the film stress and also accounts for nonlinear geometric effects which may become singificant whenever the measured deflections reach an order of magnitude equal to or greater than that of the substrate thickness. Results are presented based upon material properties and geometrical parameters that are typical for the bending-plate experiment. Comparisons are also made based upon actual experimental data that have appeared in the literature. These results clearly indicate the significance of nonlinear geometric effects in the bending-plate experiment. The model developed here may be used either to directly account for these effects or to design an experiment in such a way that these effects will be negligible. © 1990.