Effect of External Electric Field on Co Chemical Mechanical Polishing: A Reactive Molecular Dynamics Study

Cobalt (Co) boasts a low electrical resistivity, exceptional adhesion properties, and favorable thermal stability. Particularly, when the feature size of the integrated circuit (IC) is reduced to 10 nm and below, Co is deemed the most promising new-generation interconnect metal. Chemical mechanical polishing (CMP) stands as a critical surface flattening method in IC manufacturing processes. The research applies ReaxFF reactive molecular dynamics to investigate Co CMP with an electric field. Co electrochemical mechanical polishing (ECMP) reaction mechanisms are elucidated from the following perspectives. They encompass the behavior of adsorbed atoms on the Co substrate surface, the removal modes of Co atoms, and the synergistic effects of the load and electric field on Co atom removal. The findings reveal that the adsorption of H₂O layers impacts the surface charge distribution of Co. The electric field alters the microscopic structure of H₂O molecules and the atomic charge state of Co. During the polishing process, H₂O molecules move along with the abrasive, consequently elevating Co atoms. Upon reaching a certain height, Co atoms bond with an abrasive and are subsequently removed. To some extent, the removed atoms aid in the removal of other Co atoms on the surface. Under low load conditions, electric fields adversely affect atomic removal. However, as the load increases, the positive effect of the electric field on atomic removal becomes evident. Substrate internal damage tends to escalate with increasing mechanical loads. However, the application of an electric field effectively suppresses subsurface damage while enhancing the polishing quality of Co. In our research system, effective material removal can be achieved while minimizing substrate damage under a 0.1 V/Å electric field and 40 GPa pressure. This study contributes to a deeper understanding of the polishing mechanism during Co ECMP.