Investigation of the Mechanical Properties and Adhesion of P.V.D. Tungsten Films on Si and Silicon Compounds by Bulge and Blister Tests

Abstract

P.V.D. tungsten films deposited on silicon wafers (covered or not with a P.E.C.V.D. silicon oxide, nitride or oxynitride sublayer) were submitted to bulge and blister tests. The mechanical equilibrium and geometry of the bulged tungsten membranes is compared to various models. From this analysis, values of the residual stresses and the Young’s moduli in the films are derived, and found to be consistent with previous values deduced from curvature radius measurements or other mechanical test methods, as functions of the deposition conditions. Decohesion of the films from their substrates is easily observed on the W / SiO₂ / Si membranes, and the film / sublayer interfacial fracture energy is estimated about 1 J/m². This energy increases when the sublayer is changed from SiO₂ to silicon oxi-nitride and to nitride. The W / Si membranes show a much stronger adhesion than the abovementioned ones and could not be debonded before bursting.