In situ transmission electron microscopy study of thermal-stress-induced dislocations in a thin Cu film constrained by a Si substrate

Abstract

Thermal-stress-induced dislocation motion in a Cu film on an amorphous SiN x (a-SiN x ) passivated Si substrate was investigated by in situ transmission electron microscopy (TEM). Plan-view, in situ TEM experiments revealed a relatively constant dislocation density of 3.4×10 9–5.9×10 9 cm −2 throughout thermal cycling. However, dislocation motion was strongly temperature dependent. At elevated temperatures dislocation moved continuously, while at temperatures below ∼220°C dislocation motion became jerky with a projected mean free path of ∼70 nm. Furthermore, cross-sectional TEM specimens revealed that dislocations were attracted and pulled into the Cu/a-SiN x interface, where upon dislocation contrast disappeared. The limited dislocation mobility observed at low homologous temperatures may contribute to the high yield stress of the Cu films.