The Model of the Process of the Chemical Mechanical Polishing of the Copper Metallization, Based on the Formation of the Passivation Layer

Abstract

A new model of the interaction of an active suspension with a copper surface during the process of the chemical-mechanical polishing (CMP) of the copper metallization is developed. The manner of the formation and growth of the passivation layer is entered and quantitatively examined for the first time, and its impact on the polishing rate is analyzed. The main stages of the chemical effect of the suspension entered in the models are investigated: diffusion of Cu⁺ ions and tunneling of the conduction electrons of copper through the passivation layer to its boundary with the suspension and also the chemical reactions in the suspension near the surface of the passivation layer, resulting, on the one hand, in an increase of its thickness, and, on the other hand, in its decrease due to the formation of soluble copper compounds and their removal from the reaction zone. The results are used to describe the CMP of the surface of the copper metallization in the (K₃Fe(CN)₆ + NH₄OH) suspension. The closed system of kinetic equations of the CMP, including a description of the variation with time of the thickness of the passivation layer is obtained; the solutions of this system in the steady-state mode, in the cases of practical importance, when either the diffusion of the Cu⁺ ions in the passivation layer or their electromigration are predominant are found and analyzed. Estimations of the polishing rate and maximal thicknesses of the passivation layer consistent with the experimental data are obtained.