A design of green slurry for copper/cobalt barrier-step chemical mechanical polishing with controlled removal selectivity and dynamic galvanic corrosion inhibition

Abstract

Chemical mechanical polishing (CMP) is one critical process in chip fabrication while also regarded as highly polluting due to the toxic CMP slurries. Though green slurries were recently proposed and developed, few of them could satisfy the stringent requirements of the simultaneous planarization of copper/cobalt heterogeneous structure, especially in technology node below 14 nm. In this contribution, a green CMP slurry with a biodegradable chelator methylglycinediacetic acid (MGDA) and a plant-extract inhibitor disproportionated rosin (DR) was designed. Nanometer-scale smooth surface, removal selectivity, galvanic corrosion inhibition and residual control was realized with the developed slurry. Through comprehensive experiments and theoretical calculations, the roles of the ingredients played and their synergistic material removal mechanism were elucidated. MGDA partially dissolved the oxide film, especially Cu(OH)₂ formed by H₂O₂ and the porous film could be more easily removed by the mechanical friction of abrasive particles. DR ensured post-polished surface quality by inhibiting over-corrosion through adsorption on copper surface. Density-functional-theory calculations analyzed DR's molecular reactivity and determined the most stable parallel adsorption configuration. The work provides useful insights into the fundamental interactions of components in CMP process. In addition, both MGDA and DR are commercially available with low cost, showing great practical application prospect in low-technology-node chip fabrication.