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Effect of Organic Acids in Copper Chemical Mechanical Planarization Slurry on Slurry Stability and Particle Contamination on Copper Surfaces

The purpose of this study was to investigate the effect of organic acids in alumina-based slurry on the stability of slurry particles and particle contamination on a wafer surface after Cu Chemical Mechanical Planarization (CMP). The electrokinetic behavior of alumina particles in the presence and absence of organic acids was studied. When organic acids were added to slurries, the charge reversal of zeta potential was measured on alumina particles in acidic pH ranges. The stability of alumina particles was seen to be dependent on the type of organic acid added to the slurry. An unstable suspension of particles was observed when oxalic and succinic acids were added to the slurry. The presence of citric acid led to a stable suspension of alumina particles in the slurry. The sedimentation rate of particles was calculated to be the slowest in the citric-acid-added slurry. No increase of particle size was measured in the slurry containing citric acid. A rapid increase of mean particle size was found when oxalic and succinic acids were added to the slurry. The addition of citric acid in the slurry effectively prevented a slurry particle contamination from the Cu surface after Cu CMP.