Leveling of Microvias by Electroplating for Wafer Level Packaging

Abstract

The filling of microvias with diameters between 30 and 100 µm and aspect ratios up to 2.5 in silicon wafers, was investigated to determine the performance of copper electroplating. An electrolyte with a low leveler concentration was only suitable for filling microvias with aspect ratios below 1. An increase of the leveler concentration enabled the filling of microvias with higher aspect ratios. The fill-up evolution shows a bottom-up plating behavior. Electrochemical measurements show that for conditions prevailing at the bottom of the via, the electrodeposition rate is enhanced while for conditions prevailing at the top, it is inhibited. This difference originates from a concentration gradient of leveler inside the via and different convection conditions inside and outside the via.