The physical improvement of copper deposition uniformity with the simulation models

Abstract

The large-scale square wafer electroplating process was analyzed using the finite element method (FEM) in COMSOL Multiphysics®. The distribution of deposition thickness on the wafer was assessed using the Non-Uniformity (NU%). Several modifications were made to the geometry of the electrolyte tank, including anode mask, cathode mask, and auxiliary cathodes (firewalls), to enhance the uniformity of deposition thickness. In terms of the kinetic aspect, the current distribution modules employ the Butler-Volmer equation to depict the current density and overpotential on the wafer. The Electrode Shell approach was utilized to account for the reduction in internal wafer resistance resulting from the growth of the copper seed layer. This enabled a more accurate simulation of the potential distribution on the wafer, bringing it closer to real-world conditions. Through the analysis of experimental data using three different models, it was observed that Model 2, which incorporated a coupled Electrode Shell with Secondary Current Distribution, provided the best simulation results for this experiment. The NU% value obtained from the experiment was 23.81%, which compared favorably to the simulated value of 23.46%. Consequently, the accuracy of the simulation reached an impressive 98.5%.