Effect of organic acids on copper chemical mechanical polishing

In chemical mechanical polishing (CMP) of Cu, organic acids are often used as additives of slurries. This paper studied the effects of citric acid, oxalic acid, glycolic acid and glycine on Cu CMP performance. Our experiments explored the difference of these organic acids in surface reactions with Cu. The results showed that organic acids could chelate the passive film of Cu, and oxalic acid would further form precipitates with copper ions to change the chemical and mechanical action during CMP. Potential-pH diagrams, electrochemical polarization and impedance analyses were used to examine the behaviors of Cu in various organic acid slurries. The results indicated that the proposed equivalent circuits from impedance analysis for Cu CMP system could provide a good index to surface roughness. Furthermore, we also discussed the effects of used organic acids on reducing particle contamination after Cu CMP by measuring the difference of isoelectric points between Cu and α-Al2O3. The result showed that the addition of organic acid could efficiently decrease particle contamination.