INFLUENCE OF SURFACE CONTAMINATION ON METAL METAL BOND CONTACT QUALITY/

The influence of surface cleanliness of Au/Ni coated multichip materia ls (MCMs), Ag plated Cu lead frames, and Al bond pads on semiconductor chips ion the strength of Au wire bond contacts has been investigated . A clean surface is important for good adhesion in any kind of attach ment process. Investigations by means of x-ray photoelectron spectrosc opy have been Performed on the bond substrates to determine the chemic al composition, the nature as well as the thickness of the contaminati on layer. The influence of contamination on bond contact quality has b een examined by pull force measurements, which is an established test method in semiconductor packaging industry for evaluating the quality of wire bonds. The results clearly show that a strong correlation betw een : the degree of contamination of the substrate and pull strength v alues exists. Furthermore, a contamination thickness limiting value of 4 nm for Au and Ag substrates was determined, indicating good wire bo nd contact quality. The effect of plasma cleaning on wire bondability of metallic and organic (MCMs) substrates has been examined by pull fo rce measurements. These results confirm the correlation between surfac e contamination and the strength of wire bond contacts for Au/Ni coate d MCMs and Ag plated Cu lead frames. Atomic force microscopy measureme nts have been performed to determine the roughness of bond surfaces, d emonstrating the importance of nanoscale characterization with regard to the bonding behavior of the substrates. Finally, bonding substrates used in integrated circuit packaging are discussed with regard to the ir Au wire bonding behavior. The Au wire bonding process first results in a cleaning effect of the substrate to be joined and secondly enabl es the change of bonding energy into frictional heat giving rise to an enhanced interdiffusion at; the interface.