Profile of the wafer level ECD gold bumps under variable parameters

The uniformity and deformation of electrochemical deposition (ECD) bumps get more and more important with the pitch shrinking and density increasing according to the requirement of modern electronic industry. In this paper, wafer level diameter and thickness distribution, surface roughness and hardness of Au bumps were characterized under different electroplating current densities and bath temperatures. Some valuable results were obtained. First, the diameter of ECD Au bumps was enlarged for 5-30 mu m at all positions on the wafer for both the bumps of 10-100 mu m diameters. Electroplated at 40 degrees C, the diameter distribution of Au bumps was similar to that of photoresist. While electroplated at 60 degrees C, its distribution was more symmetric. Second, more uniform thickness distribution of Au bumps was obtained when the bath temperature increased from 40 to 60 degrees C or the electroplating current density decreased from 8 to 3 mA/cm(2). Third, the Au bumps electroplated at 60 degrees C exhibited the surface roughness of 105-125 nm independent of electroplating current densities. The Au bumps electroplated at 40 degrees C exhibited the surface roughness of 40-45 nm for 3 mA/cm(2) and 5 mA/cm(2) and 923.45 nm for 8 mA/cm(2). Fourth, the hardness of Au bumps decreased with electroplating temperature increasing from 40 to 60 degrees C. The difference of hardness got at between 40 and 60 degrees C can be vanished by the following anneal process at 60 degrees C. In addition, the big differences among different current densities electroplated at 40 degrees C can also be vanished by the anneal process. Finally, possible reasons leading to above results were discussed.