Thin films can develop large residual stresses during their growth that significantly impact their performance. Therefore, there is a need to understand how the stress is related to the developing film structure and underlying kinetic processes. In this work, we describe measurements of stress and the corresponding grain structure during electrodeposition of Ni and Cu films. For Ni deposition, the grain size stays nearly constant during growth and the stress reaches a nearly constant steady-state. For Cu deposition, the grain size grows as the thickness increases and the microstructural evolution affects the evolution of the stress. To remove the effect of subsurface grain growth on the stress, measurements were also done with periodic pauses that allowed the stress induced by grain growth to saturate. We interpret the results in terms of a kinetic model for stress evolution that focuses on the developing boundary between adjacent grains while the film is deposited. The effect of grain growth on stress for different types of microstructural evolution is also discussed. After accounting for the stress from subsurface grain growth, the results are consistent with the model for the dependence on growth rate and grain size at the surface.

Residual stress during thin film deposition is affected by the evolution of the microstructure. This can occur because subsurface grain growth directly induces stress in the film and because changing the grain size at the surface affects the stress in new layers as they are deposited. We describe a new model for stress evolution that includes both of these effects. It is used to explain stress in films that grow with extensive grain growth (referred to as zone II) so that the grain size changes throughout the thickness of the layer as the film grows. Equations are derived for different cases of high or low atomic mobility where different assumptions are used to describe the diffusion of atoms that are incorporated into the grain boundary. The model is applied to measurements of stress and grain growth in evaporated Ni films. A single set of model parameters is able to explain stress evolution in films grown at multiple temperatures and growth rates. The model explains why the slope of the curvature measurements changes continuously with thickness and attributes it to the effect of grain size on new layers deposited on the film.

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This work quantifies the dependence of residual stress in electrodeposited Cu on the grain size and the growth rate. The stress was measured during growth at different rates using wafer curvature. The corresponding grain size was determined after the growth from cross-sectional micrographs. The measurements at different growth rates included pauses that allowed stress changes from grain growth to be separated from the growth stress. The results are analyzed in terms of a kinetic model that predicts the dependence on the growth conditions. This explains the complex interrelationship between growth rate and grain size in determining the stress.

Measurements were performed to study the influence of growth rate (plating current), grain size, and electrolyte concentration on stress evolution in Ni electrodeposited from an additive-free Ni sulfamate bath. The stress measurements were conducted by the wafer curvature method during electroplating, and the corresponding grain sizes were determined post-deposition from crosssections made using a Focused-Ion Beam (FIB). The results were interpreted using a kinetic model which focuses on the incremental stress generated at the triple junction where adjacent islands impinge upon each other. The stress vs. growth rate does not change significantly when the Ni sulfamate concentration was changed at fixed boric acid concentration, but it did change when the boric acid concentration was altered. This is discussed in terms of the effect of the electrolyte concentration on the exchange current and interfacial energy.

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An analytical model for the evolution of residual stress in polycrystalline thin films is used to analyze numerous previously reported wafer curvature measurements obtained for a variety of materials and processing conditions. The model, which has been described in previous publications, considers stress-generating mechanisms that occur at the grain boundary as it forms between adjacent grains and stress due to the subsurface grain growth in layers that have already been deposited. Current work extends the model to include different types of microstructural evolutions. A set of parameters for each dataset is obtained by non-linear least square fitting. Model parameters that are not expected to depend on the processing conditions are constrained to have a common value when fitting the multiple datasets for each material. The dependence of the fitting parameters on the material and process conditions is evaluated and compared with the physical mechanisms implemented in the model.

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