In situ stress measurements during copper electrodeposition on (111)-textured Au

In situ stress measurements were made during copper electrodeposition onto (III)-textured Au from acidic sulfate electrolyte using the wafer curvature method. In the Cu underpotential deposition region, the intermediate (root 3 x root 3)R30 degrees Cu-sulfate honeycomb structure creates a surface stress that is tensile when compared to that of the sulfate-adsorbed electrode at positive potentials or the complete (1 x 1) Cu monolayer at more negative potentials. This behavior is consistent with surface-induced charge redistribution models that appear in the literature. During the bulk deposition of Cu, there is a rapid increase in tensile stress during the first 20 nm of growth that we attribute to nuclei coalescence and grain boundary formation. The magnitude of the tensile stress as well as the film thickness at which the maximum stress occurs are both dependent upon the electrode potential due to its influence on the nucleation density. When the films are continuous, the total stress is the superposition of the coalescence-induced tensile stress and a compressive stress which we attribute to the incorporation of mobile adatoms on the surface into the grain boundaries. The tensile stress component dominates thin films deposited at high overpotential, whereas thick films deposited at low overpotential have a net compressive stress. When deposition is interrupted both tensile and compressive components of the stress relax somewhat but are quickly reestablished when deposition is resumed. The development of the growth stress that we describe here is very similar to that which has been reported for Cu deposition from the vapor phase. (c) 2005 The Electrochemical Society. All rights reserved.