Electrochemical-mechanical planarization of copper: Effects of chemical additives on voltage controlled removal of surface layers in electrolytes

摘要

Chemical-mechanical planarization (CMP) of copper has now become an integral part of materials processing in the fabrication of integrated circuits. This process requires the application of a considerable down-force to the sample in its polishing step, and hence could be unsuitable for systems containing mechanically weak dielectric layers under the Cu lines. Recently, electrochemical-mechanical planarization (ECMP) has emerged as a possible extension of CMP, where through voltage-activated removal of Cu surface layers, one can substantially minimize the down-force necessary for mechanical polishing. However, the detailed electrochemical factors that are central to designing efficient abrasive-free electrolytes for ECMP are not clearly understood at the present time. In the present work, we address this issue by studying the relative electrochemical effects of different chemical additives in a peroxide based glycine solution commonly used in CMP slurries for Cu. More specifically, our analysis focuses here on the individual and combined roles of NO_3~- (background anion), H_2O_2 (oxidizer) and glycine (complexing agent) in voltage controlled material removal from Cu in the absence of mechanical polishing.