Oxide Removal

With regard to electrical yield the copper oxide resistance is proportional to the oxide content on the copper surface, hence Cu2O reduction is paramount. Hydrogen (H2) microwave plasma or gas mixtures thereof (ArH2), forming free hydrogen radicals provides a field proven plasma technology used today in chip packaging. The chemical effects of the microwave plasma create free hydrogen radicals forming new volatile molecules form surface atoms of the Cu bump, recombining to for example water vapor (H2O) and being removed from the process chamber. Thus the hydrogen radicals in the low temperature microwave plasma sufficiently reduce the oxide, layer by layer from the surfaces of the bond interface. One additional benefit of the dry chemical oxide reduction process is low temperature exposure to the device. In high volume production the microwave plasma can maintain a process temperature <60°C.