Ultraviolet catalysis assisted chemical mechanical polishing of cobalt: Mechanism of corrosion inhibition and atomic-level planarization

Abstract

As the feature sizes of integrated circuits shrink to 5 nm node and below, interconnection fabrication is approaching atomic-level precision requirements. Cobalt (Co) has emerged as a key interconnection material to replace copper due to its superior electrical property. However, achieving an atomically smooth Co surface remains challenging. This work modifies the conventional chemical mechanical polishing (CMP) process by introducing ultraviolet catalysis (UV-CMP). The approach precisely controls the oxidation process of the Co surface via UV irradiation, enabling the formation of a protective passive layer that effectively inhibits corrosion. Experiments demonstrate that UV irradiation catalytically activates H2O2 to generate highly reactive hydroxyl radical (·OH), facilitating the rapid formation of a dense and protective Co3O4 passivation layer on Co surface. Under the optimized condition, the in-situ formed passivation layer effectively suppresses corrosive dissolution and yields an atomically smooth surface with a roughness as low as 0.15 nm, representing a nearly 50 % reduction compared to the non-UV-irradiated case. Electrochemical measurements confirm the highest charge transfer resistance under the optimal condition, corroborating the exceptional surface protection capability of the passivation layer. Density functional theory (DFT) calculations reveal that ·OH exhibits a much stronger electron-withdrawing capability than H₂O₂ on various Co surfaces, promoting substantial electron transfer from Co and thereby driving the surface to a higher oxidation state. This work elucidates the mechanism of photocatalytic passivation in the CMP of Co, thereby providing both theoretical insights and technical support for the atomic-level precision surface fabrication of Co interconnects at advanced technology nodes.