Electrolyte Composition for Cu Electrochemical Mechanical Planarization

Abstract

Cu electrochemical mechanical planarization (ECMP) is currently being investigated to replace or supplement Cu chemical mechanical planarization (CMP) due to the introduction of porous low- dielectric materials, which may not withstand the mechanical force applied during conventional CMP. Electrolytes for Cu ECMP at pH 3 containing 5-phenyl-1-H-tetrazole (PTA), hydroxyethylidenediphosphoric acid, and oxalic acid are investigated using electrochemical methods and polishing of Cu-coated blanket and patterned wafers. The Cu removal rate and the planarization efficiency during Cu ECMP can be approximated using electrochemical measurements of the Cu removal rate, with and without surface abrasion. These results predict a potential window within which the Cu removal rate is greater than and the planarization efficiency is greater than 0.90. However, high planarization efficiencies are only obtained when silica abrasives are included within the ECMP electrolyte. In situ electrochemical impedance spectroscopy results indicate that the interfacial impedance is increased by the presence of silica, suggesting that silica is incorporated into the PTA-based passive film and is thus needed for effective planarization. Electrochemical quartz crystal microbalance experiments indicate that PTA may provide better Cu surface passivation at a high anodic potential than benzotriazole, which is widely used during Cu CMP.