Additives Co-Injection: A Test for Determining the Efficacy and Process Parameters of Bottom-up Plating

Abstract

The additives co-injection test is shown to provide important and unique insight into the bottom-up plating process. The observed transient peak polarization depends on the convective flow and reflects the electrode coverage by both the suppressor and the anti-suppressor species, much like the electrode coverage during the actual bottom-up plating process. A computer implemented analytical model of the co-injection test is presented. This model, which accounts for the additives transport through the flow-induced boundary layer and their adsorption kinetics, characterizes the actual wafer plating process more comprehensively than previous models, linking for the first time the wafer rotation rate to the process effectiveness. Correlating the model to experimental data provides the values of process parameters, including additives adsorption rates and their displacement constants, which heretofore were not accessible. It is found that previously reported values of diffusivities, saturated surface coverages, and the SPS adsorption rate constant are consistent with the presented co-injection model, however, values for the rate constants of PEG adsorption (kPEG) and PEG displacement by SPS (kSPS,PEG), which previously have only been inaccurately estimated, are now correctly quantified. The newly derived values are 10 cm/s and 2.0 × 10−6 cm/s for kPEG and kSPS,PEG, respectively.