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.
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•Microstructural evolution during thin film growth affects the corresponding evolution of stress.•Stress is modified by the changing grain size at the surface and grain growth below the surface.•Measurements with pauses allow grain growth to saturate and eliminate its effect on the stress.•A kinetic model explains the dependence of the stress on the growth rate and grain size at the surface.
Sputtering of an amorphous or crystalline material by an ion beam often results in the formation of periodic nanoscale ripple patterns on the surface. In this Letter, we show that, in the case of ...alloy surfaces, the differences in the sputter yields and surface diffusivities of the alloy components will also lead to spontaneous modulations in composition that can be in or out of phase with the ripple topography. The degree of this kinetic alloy decomposition can be altered by varying the flux of the ion beam. In the high-temperature and low-flux regime, the degree of decomposition scales linearly with the ion flux, but it scales inversely with the ion flux in the low-temperature, high-flux regime.
We present a model for compressive stress generation during thin film growth in which the driving force is an increase in the surface chemical potential caused by the deposition of atoms from the ...vapor. The increase in surface chemical potential induces atoms to flow into the grain boundary, creating a compressive stress in the film. We develop kinetic equations to describe the stress evolution and dependence on growth parameters. The model is used to explain measurements of relaxation when growth is terminated and the dependence of the steady-state stress on growth rate.
We have simultaneously measured the evolution of stress and formation of whiskers/hillocks in Sn layers using stress induced by thermal-expansion mismatch. The formation kinetics suggest that whisker ...initiation is controlled by a nucleation process. We use measurements of the nucleation rate at different stresses and temperatures to determine quantitatively how the activation barrier for nucleation is decreased by the stress in the layer.
Sn whiskers are believed to form in response to stress in layers used as protective coatings. However, what makes them form at specific sites on the surface is not known. We have used thermal ...expansion mismatch to induce stress and observe the resulting whisker formation. Cross-sectional measurements of the region around whiskers show that there are oblique grain boundaries under the whiskers that are not seen in the as-deposited columnar structure. The kinetics also suggest that the whiskering sites may be formed by a nucleation process. Based on these results, we propose a nucleation mechanism in which the boundaries of the surrounding grains migrate due to strain energy differences and create oblique boundaries at which whiskers can form. A simple model is developed to predict the stress-dependence of the nucleation rate.
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