Chemical–mechanical polishing behavior of tantalum in slurries containing citric acid and alumina

The effects of H2O2, citric acid and Al2O3 content on the electrochemical behavior, surface characteristics and metal removal rates in simulated Ta chemical–mechanical polishing (CMP) have been investigated. Electrochemical measurements indicated that Ta could be easily passivated in all citric acid base slurries prepared in this investigation. The passive film could be removed under CMP condition. The addition of H2O2 into the slurries could assist repassivation of Ta under polishing condition. X-ray photoelectron spectroscopy (XPS) revealed that the passive film formed on Ta surface in the citric acid slurries consisted of Ta2O5 and TaOH. The presence of H2O2 enhanced the formation of Ta2O5 on Ta surface. The removal rate obtained in the simulated CMP investigation increased with the amount of Al2O3, either in DI water or in the 0.01 M citric acid +9 vol.% H2O2 slurries. The surface roughness of Ta after CMP in 0.01 M citric acid +9 vol.% H2O2 slurries was higher than that in DI water base slurries when the Al2O3 content was low. A significant reduction in surface roughness combined with a high removal rate could be obtained if the Al2O3 content in the 0.01 M citric acid +9 vol.% H2O2 slurries was increased to above 10 wt.%.