Fine pitch ECD gold bumping towards future demands

Wafer level diameter and thickness distribution and surface roughness of electrochemical deposition（ECD） Au bumps were studied with variations of electroplating current densities and bath temperatures.The diameter of ECD Au bumps was enlarged at all positions and directions of the wafer.When electroplated at 40℃,the diameter distribution of Au bumps was similar to that of photoresist.While electroplated at 60℃,its distribution was more symmetric.Secondly,more uniform thickness distribution of Au bumps was obtained when the bath temperature increased from 40℃ to 60℃ or the electroplating current density decreased from 8 mA/cm² to 3 mA/cm².Thirdly,the Au bumps electroplated at 60℃ exhibited the surface roughness of 130-160 nm independent of electroplating current densities.The Au bumps electroplated at 40℃ exhibited the surface roughness being dramatically increased from 82 nm to 1572 nm with electroplating current density increasing.