Impact Factors on Low Temperature Cu-Cu Wafer Bonding

Physical mechanism of Cu-Cu wafer bonding was studied as a base for low temperature (<200 degrees C) wafer bonding process optimization. It was found out that for the successful bonding of two copper surfaces the following (classes of) impact factors have to be considered (I) contacting, even at atomic scale, (II) cleanliness of the surface, (III) diffusion enhancing materials properties and (IV) process conditions. From these fundamental findings subsequently low temperature metal thermo-compression Cu-Cu wafer bonding and even room temperature direct bonding was facilitated.