Synergist effect of potassium periodate and potassium persulfate on improving removal rate of Ruthenium during chemical mechanical polishing

摘要

As technology nodes continue to decrease, traditional Copper (Cu) interconnects in the back end of the line (BEOL) will encounter more and more problems. Ruthenium (Ru) is expected to be a barrier layer or even as a novel type of interconnection material because of its good electrical properties. However, because of its high chemical inertness, Ru is challenging to achieve a higher removal rate in the chemical mechanical polishing (CMP) process. In this study, the synergist effect of potassium periodate (KIO_4) and potassium persulfate (K_2S_2O_8) on the removal rate of Ru during CMP was investigated. The theory of advanced oxidation process (AOPs) is used to explain the reaction process of Ru with KIO_4 and K_2S_2O_8. X-ray photoelectron spectroscopy (XPS) combined with electrochemical are applied to explore the removal machanism and chemical reaction mechanism of Ru under the synergistic effect of KIO_4 and K_2S_2O_8. The CMP tests shows that the Ru removal rate (1123 A/min) in the presence of KIO_4 and K_2S_2O_8 composite could be increased by more than 221% compared to the removal rate (507 A/min) of KIO_4 alone. In addition, Ru oxidation process is more affected by diffusion-controlled. Excessive oxidant concentration will reduce the removal rate of Ru. The mechanism analysis shows that the RuO_3-activated persulfate generates sulfate radical (SO_4~-·), which can further generate more oxides on the Ru surface, and Ru oxide is easily removed under the CMP process. Therefore, the Ru removal rate will be significantly improved. Simultaneously, the surface roughness Sq can be reduced to 0.667 nm after polishing.