An experimental study of the behavior of additives (chloride(-), PEG and SPS) during acidic copper electrodeposition

This dissertation documents an experimental investigation of additive behavior in acidic copper electroplating solutions containing chloride ions, polyethylene glycol (PEG), and bis-3-sodiumsulfopropyl disulfide (SPS). These solutions represent a simplified model of industrial electroplating solutions used to achieve superfilling in the fabrication of copper on-chip interconnects. In this study, a mechanism describing the interactions between additives and the copper surface has been developed to describe the additive-driven superfilling process.; Galvanostatic and potentiostatic electrodeposition experiments were conducted in the presence of a single additive, two additives, or three additives with use of a rotating disk electrode. The influence of the potential on copper deposition in the presence of additives was investigated by linear sweep voltammetry, as well as current-step and potential-step experiments. The complexity of the additive surface interactions was revealed by these carefully designed copper deposition experiments, as well as by surface analytical techniques including SEM, AFM, and XPS. In addition, copper deposition onto submicron trenches was performed and the results were successfully explained and predicted.; Experiments show that superfilling is a transient phenomenon resulting from the fact that depolarization occurs faster inside than outside of the cavity. The transient behavior was found to be a strong function of SPS concentration, applied potential and mass transport, and appears to be the result of slow accumulation of an SPS-related accelerator. It appears that the surface accumulation of the SPS-related acceleration does not readily occur in the presence of Cl-, and that PEG interacts with Cl- to enable slow accumulation of the accelerator. A key element of the mechanistic explanation developed in this study is that acceleration in the Cl-PEG-SPS system is due to the Cu(I)-thiolate complex Cu-SR which is formed by the electrochemical conversion of SPS to mercaptopropanesulfonate acid (MPSA), followed by the chemical reaction of MPSA with cupric ions. This mechanism is consistent with all the experiments examined, many of which cannot be explained by mechanisms predating the current study. This mechanism furthers the theoretical understanding of copper deposition and provides a foundation for better control of the superfilling process and accurate prediction of superfilling results.