Mechanisms of multiple functional groups in post-CMP cleaning solutions for Co interconnects

Abstract

Cobalt (Co) exhibits low resistivity, excellent adhesive properties, and the ability to fill gaps seamlessly, thus it is promising to change the landscape of integrated circuits in various fields, especially in the areas of interconnections and logic contacts. The cleaning of Co surfaces after chemical mechanical polishing (CMP) is an essential step due to the potential occurrence of numerous defects, such as silicon dioxide nanoparticles, organic residues, and severe corrosion. This research delves into the mechanisms of pivotal components in cleaning solutions, including complexing agents and corrosion inhibitors, and analyzes their impact on cleaning effectiveness. Based on Derjaguin-Landau-Verwey-Overbeek theory calculation and adhesion force measurements through the liquid mode of atomic force microscope, the interaction forces between silica (SiO₂) particles and Co substrate were calculated and verified. Additionally, various methods were employed to unravel the nature of the particles and the mechanism of different functional groups, encompassing electrochemical experiments, static etching tests, surface energy studies, zeta potential measurements, and X-ray photoelectron spectroscopy characterization. This comprehensive investigation offers a clear understanding of the roles played by different functional groups, establishes a functional group system for cleaning solutions tailored to Co interconnect wafers, and provides valuable guidance for the subsequent design and development of cleaning solutions.