Ar/N2 Plasma Induced Metastable CuxNy for Cu-Cu Direct Bonding

Abstract

Metal-metal bonding is a promising bonding technique in semiconductor processing. In this work, we report Ar/N2 plasma induced metastable CuxNy for Cu-Cu die-die direct bonding performed at room temperature in ambient environment. Surface characterizations (water contact angle, surface roughness, and XPS) are performed on the Cu surface both before and after plasma exposure. The results reveal that the Ar/N2 plasma induces a layer of CuxNy, and the surface of the Ar/N2 plasma activated Cu remains in an “activated” state, as shown by low contact angle, for up to 6 hours compared to that of the non-activated Cu. Subsequently, the plasma activated dies are bonded. The bonded interface is characterized by C-SAM and SEM, the bonding quality is assessed for mechanical bonding strength, hermeticity, and electrical conduction. The results support successful bonding with the desired properties. This reported bonding technology can be applied for high-throughput 3D integration and CMOS-MEMS packaging.