Environmentally clean slurry using nano-TiO2-abrasive mixed with oxidizer H2O2 for ruthenium-film chemical mechanical planarization

A colloidal silica-abrasive-based slurry mixed with periodate salts has been used for chemical mechanical planarization (CMP) of ruthenium (Ru) film in semiconductor-chip fabrication. This slurry has serious environmental problems such as generation of toxic RuO4 gas, corrosion, and ionic contamination. We developed an environmentally clean slurry using nano-TiO2 abrasive mixed with hydrogen peroxide (H2O2) for the purpose of Ru-film CMP. Moreover, this slurry is free of corrosion and ionic contamination. The polishing rates of Ru and SiO2 films with this slurry strongly depended on the H2O2 concentration; the Ru-film polishing rate rapidly increased with H2O2 concentration up to 1 wt% and then slightly decreased or saturated, whereas the SiO2-film polishing rate abruptly dropped to ∼50 Å/min. In particular, the adsorbed amount of H2O2 on nano-TiO2 abrasive directly determined the Ru-film polishing rate, indicating a new CMP mechanism of Ru film in the slurry.