Mass Transport of Leveling Agents in Plating: Steady‐State Model for Blocking Additives

A quantitative model for the leveling effects of plating additives is presented. The fundamental assumption of this model is that the coverage of adsorbed additive is controlled by mass transport. Adsorbed additive is consumed through inclusion and electrochemical reaction and hence is replaced through transport and adsorption from the bulk solution. The primary effect of the adsorbed additive is assumed to be the blocking of the deposition current at the adsorption site. This steady‐state model reproduces the unique characteristics of additive polarization curves, including hysteresis and peaks in overpotential. Three dimensionless groups which characterize additive modified kinetics are identified. The model predicts the extent of either positive leveling or growing roughness on both the micro and macro scales. Sample plating maps are presented which indicate recommended operating windows for producing smooth and level deposits for various mass transfer boundary layer thicknesses and additive compositions.