Application of contact theory to metal-metal bonding of silicon wafers

A model is presented which relates the applied load and surface roughness to the integrity of metal-metal wafer-level thermocompression bonds. Using contact theory, the true contact area is calculated as a function of the applied load and surface roughness as characterized using atomic force microscopy. The relationship between the nominal and true contact areas quantifies the effects of applied load and surface roughness on the bond integrity of the bonded wafers as indicated by the dicing yield. Experiments on Cu-Cu bonds show that the true contact area provides a better indicator of bond integrity than either the nominal contact area or applied force, taken together or separately.