Examining amino acids as environmentally friendly corrosion inhibitors for Cu and Co chemical mechanical planarization

Aliphatic amino acids (AAs) were investigated as environmentally friendly alternatives to benzotriazole (BTA) in the chemical mechanical planarization (CMP) process for Cu interconnects. The study evaluated the corrosion resistance, galvanic corrosion, and polishing removal rates (RR) for Cu and Co in a silica-based slurry containing methionine, glutamic acid, and leucine. Corrosion characteristics were determined using linear sweep voltammetry, and the removal rate was assessed by polishing wafers under controlled CMP conditions. Metal surfaces were analyzed by X-ray photoelectron spectroscopy, and scanning electron microscopy. Results indicated that the distinctive functional groups in the amino acids influenced corrosion and polishing behaviors driven by different Cu species in the passivating film layer. Methionine with its sulfur-containing side chain, exhibited exceptional inhibition capabilities by stabilizing Cu(I) species compared to Cu(II), involving a combination of physisorption and chemisorption. It also effectively controlled Cu-Co galvanic corrosion with a low igc= 0.9 mu A/cm2. Leucine, with its branched hydrocarbon chain, mitigated Cu corrosion through physisorption (20.5 kJ/mol), but increased galvanic corrosion for Co (igc = 45 mu A/cm2). Leucine formed a thin passive layer that easily broke down during the Cu(I) to Cu(II) transition. Glutamic acid, with its additional carboxylic acid group, was not effective as a corrosion inhibitor but showed a relatively low |Delta Ecorr|= 5 mV. Metal removal rates of Cu and Co followed the same trend with corrosion results. The selectivity of Cu:Co:TEOS removal with methionine was more comparable than that achieved with other additives, beneficial for Cu barrier CMP.