Dependence of pH, molecular weight, and concentration of surfactant in ceria slurry on saturated nitride removal rate in shallow trench isolation chemical mechanical polishing

We have investigated how controlling the pH, molecular weight, and concentration of the surfactant in ceria slurry affects the nitride film loss and oxide-to-nitride selectivity in the shallow trench isolation (STI) chemical mechanical polishing (CMP) process. We found that for a surfactant with a higher molecular weight, the oxide removal rate markedly decreased as the surfactant concentration increased, but in the case of a lower molecular weight, the removal rate only slightly decreased. In addition, with increasing surfactant concentration and addition of surfactant with the same molecular weight, the nitride removal rates for all slurries markedly decreased and very quickly saturated at a lower surfactant pH. Moreover, with an increase in the surfactant concentration from 0.1 to 0.3wt%, the slurries whose surfactants had a medium or the lowest molecular weight maintained higher nitride removal rates than did the slurry whose surfactant had the highest molecular weight.