In situ epitaxial thickening of wafer-scale, highly oriented nanotwinned Ag on tailored polycrystalline Cu substrates

Abstract

Highly (111)-oriented nanotwinned Ag (nt-Ag) is a promising candidate for a next-generation direct metal bonding material without a vacuum environment. However, conventional methods used for its preparation are costly, complex, and inefficient. Herein, we report an in-situ epitaxial thickening approach of wafer-scale (111) nt-Ag on tailored polycrystalline Cu substrates via a galvanic replacement reaction (GRR). The resultant Ag films replicate the crystallographic structure of the Cu substrate and exhibit local single crystallinity, which effectively protects the substrate from oxidation and achieves better bonding quality. Through detailed structural characterization and theoretical calculations, we provide insights on the counterintuitive thickening-corrosion mechanisms of GRR for the first time. We find that the interfacial interaction within the Ag/Cu becomes an additional driving force for the Ag ions to enter the lattice when the Cu substrate corrosion is inhibited. Our findings provide valuable insights into the formation and growth of nanotwin structures and can advance the future practical application of (111) nt-Ag in the microelectronics industry.