Effect of Hydrogen Peroxide on Oxidation of Copper in CMP Slurries Containing Glycine and Cu Sulfate
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Effect of Hydrogen Peroxide on Oxidation of Copper in CMP Slurries Containing Glycine and Cu Sulfate Tianbao Du, Arun Vijayakumar and Vimal Desai Advanced Materials Processing and Analysis Center University of Central Florida Orlando, FL 32816-2455 ABSTRACT This study compares the oxidative dissolution, passivation, and polishing behavior of copper chemical mechanical polishing in the presence of hydrogen peroxide, glycine and copper sulfate. High purity discs were used to study the dissolution and oxidation kinetics under static and dynamic conditions at pH 4 with varying H2O2 concentrations. Changes in surface chemistry of the statically etched copper-disc were investigated using X-ray photoelectron spectroscopy (XPS). With the addition of glycine and copper sulfate to the slurry, the copper removal rates increased significantly and the maximum removal rate shifted to a H2O2 concentration of 3%. Electrochemical investigation indicates an enhanced dissolution of copper, which might be due to the strong catalytic activity of Cu(II)-glycine complexes in decomposing H2O2 to yield hydroxyl radicals. XPS results suggest that the passivation at higher H2O2 concentrations in the presence of glycine and copper sulfate is provided by the OH radicals adsorbed on Cu surface. INTRODUCTION CMP of copper has been investigated in recent years in acidic, neutral or alkaline media (1-11). Cu CMP in a highly acidic pH regime leads to corrosion problems, while CMP in alkaline conditions is faced with selectivity issues of copper over SiO2, which results in reduced oxide thickness while over polishing. Therefore the neutral pH regime is more conducive for Cu CMP. One of the more attractive slurries in this intermediate pH regime consists of hydrogen peroxide, glycine and an abrasive either alumina or silica. Hirabayashi et al (3) demonstrated that slurries containing hydrogen peroxide, glycine and silica particles could be used for Cu CMP. The mechanism proposed by them is based on the oxidation of Cu to copper oxide by hydrogen peroxide in the recessed regions, thereby preventing the dissolution of Cu from the recessed regions. The oxide formed in the protruded regions, on the other hand, is removed by the abrasives exposing the underlying metallic surface to the slurry. The exposed Cu can react with hydrogen peroxide and glycine to form a Cu2+-glycine chelate that is soluble in water. Electrochemical and surface XPS studies have been widely used to elucidate some of the fundamental mechanisms in Cu CMP. Detailed investigations on various aspects of chemical mechanical planarization of copper have been reported lately (12, 13). Recently, it was found that, the addition of Cu salt to the slurry with H2O2 and glycine, significantly enhanced the Cu CMP removal rates. Although the catalytic role played by Cu2+-glycine complex in the decomposition of hydrogen peroxide to yield OH radicals has been investigated, the mechanism of Cu removal during CMP in the presence of H2O2, glycine and Cu ions, particularly in acidic media, is not
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