Impact of Leveler Molecular Weight and Concentration on Damascene Copper Electroplating

Abstract

The impact of leveler molecular weight and concentration on bottom-up fill rate, leveling activity, electrolyte polarization, and copper properties of films formed during damascene copper electroplating has been studied. A model leveler, polyvinylpyrrolidone (PVP), at molecular weights ranging from 3,500 to 1,300,000 and at concentrations from 1 to 20 mg/L was found to be effective in reducing excessive plated thickness over superfilling features, while resulting in little loss of bottom-up fill performance. Intermediate PVP molecular weights were most effective in reducing overplating, while the higher molecular weights enhanced fill performance. This behavior is explained in terms of leveler diffusion into features as a function of molecular weight, and leveler impact on electrolyte polarization. Incorporation of sulfur, carbon, and chloride in the plated films increased with increasing PVP concentration and molecular weight. This suggests leveling is accomplished by removal of adsorbed accelerator from the from the film surface during plating by co-deposition with leveler.