Experimental considerations for using electrochemical impedance spectroscopy to study chemical mechanical planarization systems

Chemical mechanical planarization (CMP) is routinely used in the fabrication of microelectronic devices. The surface chemistries of this technique have become quite complex with the emergence of the sub-22 nm technology nodes. While this has introduced new challenges in the field of slurry-engineering for CMP, certain electroanalytical techniques have been recognized as useful tools for the assessment of CMP slurry chemistries. In this regard, electrochemical impedance spectroscopy (EIS), a powerful probe of interfacial kinetics, can play a unique role in aiding the development/evaluation of new slurry formulations. To fully explore this capability of EIS in CMP research, it is necessary to address the experimental requirements and constraints of EIS that are linked to the mechanical component of planarization. The present work focuses on certain analytical aspects of this subject using an exploratory CMP scheme for Cu. The surface reactions of CMP are characterized here by tribologically controlled voltammetry and open circuit potentials in an alkaline slurry of H2O2 (oxidizer), guanidine nitrate (complexing agent), and colloidal SiO2 (abrasive). An experimental protocol is demonstrated to check the validation criteria of EIS for typical CMP systems. The EIS data are analyzed by complex nonlinear least square calculations, and the resulting parameters are used to corroborate the reaction mechanisms of CMP.