Effect of Noble Metal Passivation Deposited by ECD on Cu Surface for Low-Temperature Cu-to-Cu Bonding

The increasing demand for high I/O count, high performance, and low power consumption has driven the adoption of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$3\mathrm{D}$</tex> stacking technology. Achieving chip or wafer stacking requires processes such as TSV, wafer grinding, and bonding. This study investigates low-temperature Cu-to-Cu bonding and examines the effects of noble metal passivation layers deposited via electroplating (EP) and electroless plating (ELP) methods on the Cu surface. Surface analysis was conducted using XPS, GIXRD, TEM, and AFM methods. The results show that EP-Pd exhibited clear Pd peaks on the Cu surface, while no Pd peaks were detected in the ELP-Pd sample. A detailed discussion of the oxidation and diffusion behavior of noble metals like Pd and Ru, depending on the deposition methods, will be presented. Additionally, bonding was performed at 200°C with noble metal passivation layers, and the bonding interfaces were thoroughly evaluated.