Systematic Study of Surface Chemistry and Comprehensive Two-Dimensional Tertiary Current Distribution Model for Copper Electrochemical Deposition

Abstract

We present a two-dimensional, transient, tertiary current-distributionmodel for copper electrochemical deposition, with detailed surfacechemistry kinetics for the model system of copper deposition withthree representative additives; polyethylene glycol, bis-(sodiumsulfopropyl) disulfide, and hydrogen chloride. Values of kineticparameters are extracted from statistically designed rotating-disk-electrodeexperiments using a transport-reaction model of the experimentalsystem. The resulting surface chemistry description is combined withfundamental conservation laws, including transient mass transport,momentum transport, and potential distribution, to form the tertiarycurrent distribution model. Two-dimensional finite element simulationsof this model provide new insight into causes of film thickness variationsacross the wafer, including large potential variations originatingfrom the initial seed-layer thickness (terminal effect), a nonuniformmass-transport boundary-layer thickness resulting from cell geometry,and fluctuations in the additive concentrations. An application ofpulse plating is also explored. The surface chemistry and the tertiarycurrent distribution models could potentially form useful tools fordesign and optimization of copper electrochemical deposition processes.