The effect of hydrogen peroxide in a citric acid based copper slurry on Cu polishing

The removal and etching behaviors of Cu were evaluated in citric acid based slurries as functions of slurry pH and H2O2 concentration during Cu chemical mechanical planarization (CMP). In an acidic slurry (pH4), the dissolution reaction of Cu was more dominant than the passivation reaction. The static and dynamic etching rates reached their highest values at 10 vol % H2O2. The polishing rate, however, was linearly increased as a function of peroxide concentration. As the slurry pH increased to 6, the static and dynamic etching rates drastically decreased with increasing H2O2 concentrations due to the formation of thick Cu oxide as a passivation layer. The removal rate reached a maxima in slurry at 7 vol % of H2O2 then started to decrease. The removal rate of Cu was determined by both the chemical dissolution and mechanical abrasion of the passivation layer which were strongly related to slurry pH and H2O2 concentration. In the slurry of low concentration of H2O2 and low pH, the passivation layer was too thin to prevent the chemical dissolution from occurring. However, the increase of pH and H2O2 concentrations grew a thicker oxide on Cu which made the removal rates dependent on the mechanical reaction. (c) 2006 The Electrochemical Society.