High Selectivity Slurries for STI CMP

Ceria particles were synthesized by two different methods, solid-state displacement reaction method and colloidal method and used for STI CMP. Calcined abrasives were used directly as well as after milling. The effect of calcination parameters on the crystal size was measured. The effect of synthesis method and conditions on the removal rates and the selectivities are presented. Colloidal ceria and calcined ceria showed enhanced selectivity in the presence of DL aspartic acid. There is a strong correlation between the polishing behavior and the calcination temperature and a weak correlation between the polishing behavior and the duration of calcination. Titania and zirconia based slurries were also employed and they exhibited higher selectivities in presence of the additive. Our results show that other multivalent abrasives, such as titania and zirconia, exhibit chemical tooth behavior and the interaction of the additive with the chemical tooth action may explain the enhanced selectivity.