Anti-oxidative copper nanoparticle paste for Cu-Cu bonding at low temperature in air

New wide bandgap semiconductors with high working temperature demand interconnect materials that can serve at high temperature. The copper nanoparticle paste is a potential alternative interconnect material. However, it is confronted with the problem of copper oxidation. In this article, commercial copper nanoparticles with average diameter of 100 nm were first simply treated with lactic acid to remove the surface oxide and the resulting cupric lactate on the surface can prevent the oxidation of copper. Then the nanoparticles were mixed with 3-dimethylamino-1,2-propanediol to prepare an anti-oxidative copper paste. The sintered films of the paste showed good electrical conductivity. The paste can be used for Cu-Cu thermocompression bonding at low temperature in air. The shear strength of the Cu/paste/Cu samples reached 28.7 +/- 1.6 MPa after thermocompression at 225 degrees C under 8 MPa in air. The coalescence of the copper nanoparticles and the connection between copper nanoparticles and bulk copper surface were observed.