Effect of UV Radiation on Oxidation for Ru CMP

Abstract

As feature size continue to decrease, traditional copper (Cu) interconnections will encounter many problems. Ruthenium (Ru) is selected as a barrier material and even a future interconnection metal material because of its many advantages. However, due to its high hardness and chemical inertness, Ru is difficult to be removed during chemical mechanical polishing (CMP). In this study, the effect of UV-activated potassium persulfate (K₂S₂O₈) on the removal rate of Ru CMP was studied. X-ray photoelectron spectroscopy (XPS) combined with electrochemistry is used to study the removal mechanism and chemical reactions. The results show that ultraviolet rays can enhance the chemical action in the CMP process and change the removal rate. Under the condition of 80 mM, the promotion rate is about 28.01%. When the particle diameter increases to 80 nm, the removal rate is also significantly increased by about 26.36%. Mechanism analysis shows that, on the one hand, it is affected by diffusion-control. On the other hand, the surface RuO₃ and K₂S₂O₈ undergo a Fenton-like reaction under UV conditions, which makes the Ru surface loose and porous (Rq = 0.533 nm), so it is easier to remove under mechanical action.