Probing the Mechanisms of Metal CMP Using Tribo-Electroanalytical Measurements: Results for a Copper/Malonate System

Abstract

The experiments reported in this work explore certain fundamental mechanistic aspects of assessing slurry formulations for chemical mechanical planarization (CMP), an important processing step of integrated circuit (IC) fabrication. We use a model system involving abrasive-free planarization of copper (wiring material in ICs) with a pH-varied (∼6–10) CMP slurry containing malonic acid (MA, a complexer) and sodium percarbonate (an oxidizer). The analytical protocols necessary to probe such a CMP system are illustrated by combining linear sweep voltammetry (LSV), open circuit potential (OCP) transients, chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS), all operated under tribological controls of CMP. LSV helps to establish the CMP enabling reaction mechanisms. The information obtained from transient data of OCP and CA is incorporated in a phenomenological model of tribo-corrosion to further corroborate the CMP mechanism. EIS provides further verification and more details of the CMP reactions. Cu removal rates increase with increasing concentrations (0.0–0.10 M) of MA, and in agreement with a proposed CMP mechanism, exhibit a correlation with the rates of tribo-corrosion. The results illustrate a quantitative diagnostic framework for studying CMP mechanisms in the tribo-electroanalytical approach.