Multi-Die to Wafer Bonding Through Plasma-Activated Cu-Cu Direct Bonding in Ambient Conditions

In this work, we study multi-die to wafer bonding through plasma-activated Cu-Cu direct bonding carried out at room temperature in cleanroom ambient conditions. During the pre-bonding phase, surface analyses (e.g. surface profile, surface roughness, water contact angle and surface chemical states) are performed on both the as-deposited and the Ar/N2 plasma-activated Cu surfaces. It is found that the Ar/N2 plasma-activated Cu surface has lower water contact angle and surface roughness than the as-deposited Cu surface. From XPS, a thin passivation layer of CUxN is produced on the Ar/N2 plasma-activated Cu surface, which prevents the activated Cu from oxidation. The Ar/N2 plasma-activated dies are bonded onto a wafer at room temperature in ambient conditions and annealed at 300°C for 1 hour, where successful bonding is achieved. This bonding scheme shows promising features for high-throughput advanced 3D packaging and heterogeneous integration.