Effect of Bonding Pressure on the Strength of Cu/Cu Direct Bonding by Surface Activated Method

We studied Cu-Cu direct bonding for the application of 3D integration. Thin Cu film deposited specimens are bonded under high vacuum by surface activated bonding method at room temperature. In the room-temperature direct bonding process, surface roughness has a strong influence on bonding. In general, metal bonding needs high bonding pressure. For successful bonding, it is important to reveal the influence of surface roughness and bonding pressure on the bonding properties. Therefore, we investigated the relationship between surface roughness and bonding strength with bonding pressure as the parameter. The specimen with smaller surface roughness than 1nm Ra was successfully bonded by bonding pressure of 10MPa, but for bigger roughness than 1nm Ra the successful bonding needed pressure of 50MPa.