Enhancing direct metal bonding with self-assembled monolayers

A feasibility study of the application of self-assembled monolayers (SAMs) in enhancing the bondability of Au–Au thermocompression bonding at low temperatures was performed. Au stud bumps were bonded to sputtered Au surface with a thin organic layer of dodecanethiol (DDT) SAMs at temperatures ranging from 80–180 °C and pressures ranging from 225–566 MPa. The bonding strength was measured using tensile test machine. The fracture surfaces were observed and analyzed by scanning electron microscopy (SEM). Preliminary results revealed that SAMs aid in decreasing the bonding temperature for Au thermocompression bonding. From the results, it is concluded that the method realizes strong bonding at significantly lower temperatures. We believe that the SAMs help to passivate the surface after removal of organic contaminant layer by the cleaning solution, preventing the formation of contaminant layers which hinder bonding, and facilitating the whole contact area bonding of Au–Au joint.