Chemical mechanical polishing of copper and tantalum was performed using fumed amorphous silica abrasive particles dispersed in H2O2, Fe(NO3)3, and glycine solutions. Results showed that in DI water silica did not polish Cu but Ta had a relatively high polish rate. Cu polish rate decreased with increasing particle concentration in Fe(NO3)3-based slurries due to the adsorption of Fe3+ on the silica surface. Addition of H2O2 enhanced Cu polish rate but reduced Ta polish rate. The specific surface area of the particles played an important role in the removal of Ta and Cu, presumably due to some chemical bonding between the materials being polished and the silica particles.