Improving copper electrodeposition in the microelectronics industry

The sporadic voiding phenomenon in Cu₃Sn intermetallic compound (IMC) formed during thermal aging, sometimes referred to as "Kirkendall voiding", has been found to lead to degradation of solder joint reliability in board level shock testing. It was suggested that the voiding phenomenon resulted from the incorporation of specific impurities in the copper during electroplating. In this study, Cu samples were electroplated from a generic suppressor-brightener additive system using a rotation disk electrode (RDE) apparatus. Overpotential during plating, surface morphology and the propensity for voiding of plated samples were investigated. Galvanostatic (constant current density) plating was conducted at 10 mA/cm² sequentially up to 18 hours. The solution exhibited dependences of overpoential and voiding propensity on bath aging, due to the breakdown of the organic additives. Cu samples were also plated in the current density range of 0.8-40 mA/cm². In the 10-20 mA/cm², current density range, a fine-grain, smooth, deposit surface was observed, accompanied by an especially low voiding level of samples plated in that range.