Two-Step Ar/N2 Plasma-Activated Al Surface for Al-Al Direct Bonding

In this study, two-step argon/nitrogen plasma-activated aluminum surface for aluminum-aluminum direct bonding is reported. Surfaces from the as-deposited and the argon/nitrogen plasma-activated aluminum are characterized for hydrophilicity and surface chemical states. The results demonstrate that the plasma-activated aluminum surface has smaller water contact angle at 8° (i.e. more hydrophilic) and a thin layer of aluminum nitride. Moreover, the bonded plasma-activated dies, annealed at 300°C under 2000 mBar, have an impressive mechanical bonding strength of ~32 MPa with superior bonding quality. This plasma-activated bonding process is fast (10 s), requires low bonding force (50 N) and can be carried out in cleanroom environment, indicating its full promise for high-throughput heterogeneous integration and advanced packaging.