Glycerol surface pretreatment enabled Cu-Cu low-temperature direct bonding in ambient air

The broad application of Cu-Cu direct bonding is substantially constrained owing to the propensity of copper to oxidize, coupled with complex processes including elevated bonding temperatures and compulsory protective atmospheres. Glycerol is employed to diminish Cu oxide while concurrently preserving the reduced Cu surface in ambient air. Cu-Cu direct bonding was thus accomplished at a lower temperature range (150 °C–200 °C) in ambient air, leveraging glycerol pretreatment for the reduction and protection. The effectiveness of glycerol in curtailing the surface oxidation of Cu at 200 °C in ambient air was discovered. The bonding strength exhibited a steady increase from 19.5 MPa to 32.6 MPa as the bonding temperature escalated from 150 °C to 200 °C. Furthermore, in the case of bonding at 200 °C, the bonding interface presented a dense, continuous nature with minimal oxide and carbon residue. Concurrently, good electrical properties were observed at the bonding interface.