Abstract
Copper (Cu) is an important conductive material used in microelectronic integrated-circuit devices due to its high electrical conductivity and low cost. However, Cu also suffers some intrinsic drawbacks such as oxidation and fast atomic diffusion, which would degrade device performance and even cause reliability problems. Cu metallization with highly dense nanoscale twin boundaries (nanotwinned Cu) have received wide attention because it possesses some excellent properties such as high tensile strength, good electromigration resistance and excellent thermal stability. However, few studies have addressed the chemical property of twin-modified Cu surface, especially for the nanotwinned Cu nanowires (nt-CuNWs). In this study, we investigate the chemical reactivity and structure stability of nt-CuNWs under moistured air ambient, water and acidic solution. The microstructural evolution and oxide formation behavior of nt-CuNWs were ex-situ monitored by transmission electron microscopy. By comparing the nt-CuNWs and nanocrystalline CuNWs (nc-CuNWs), it is found that the former exhibits a zig-zag faceted structure with very low atomic step density, while the latter have an atomically rough surface with high atomic step density. The nt-CuNWs appear to have reduced chemical reactivity and enhanced resistance to chemical corrosion. On the other hand, the nc-CuNWs were gradually oxidized by forming cuprous oxide (Cu2O) under water or moisture environment, which decomposed and transformed into Cu nanoparticles when exposed to visible light. According to the photoelectrochemical reaction of Cu/Cu2O system, we found that the nt-CuNWs demonstrate high chemical stability against the photolytic reaction. A kinetic mechanism based on the low chemical reactivity of twin-modified Cu surface and effective Cu/Cu2O interfacial vacancy sinking is proposed to explain why the nt-CuNWs are resistant against Kirkendall void formation.