STRESS EVOLUTION IN PASSIVATED THIN-FILMS OF CU ON SILICA SUBSTRATES

Stresses supported by thin films of Cu passivated by SiOx, have been m easured upon thermal cycling. Very high stresses have been found, appr oaching 1 GPa in the thinnest (40 nm) films. Strengthening beyond yiel d occurs upon both cooling and healing, indicative of strong strain ha rdening in the Cu. The hardening continues down to at least 77 K. The yielding behavior of the Cu films has been characterized by a kinemati c constitutive law, with exceptional strain hardening and a convention al temperature-dependent yield strength. The physical basis for this b ehavior is ascribed to confined shear bands in the Cu that induce larg e back stress. Transmission electron microscopy reveals aligned disloc ations, which seemingly dictate the inelastic deformations in the shea r bands.