Influence of Initial Microstructure on Thermomechanical Fatigue Behavior of Cu Films on Substrates

Display Omitted We follow the texture changes of grains in Cu thin films during thermal cycling.Repeated thermal cycling leads to severe surface roughening and a change in texture.Epitaxial Cu film show no surface degradation and maintain their initial texture.Orientation changes and surface damage evolution are explained classical slip induced lattice rotation.Lattice rotation is assisted by anisotropy of Cu, dislocation plasticity and diffusion. During a switch event in a power semiconductor device temperature changes of up to 300K can occur in the Cu layer. Repeated switching operations causes cyclic thermal cycling which may finally lead to thermomechanical fatigue with severe microstructural changes. In this study, the influence of the starting microstructure and film thickness (600nm and 5000nm) on thermomechanical fatigue was investigated for epitaxial and polycrystalline Cu films for up to 1000 thermal cycles. Severe surface roughening and a texture change (crystal rotation) are detected during thermal cycling for the polycrystalline Cu films, while the epitaxial films maintain their microstructure. Controlling the initial microstructure of a Cu layer in a device exposed to cyclic thermomechanical straining is a route to delay surface damage.