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

Thermal-stress-induced dislocation motion in a Cu film on an amorphous SiNx (a-SiNx) 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 3.4×109–5.9×109 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-SiNx 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.