Residual Stress in Electrodeposited Cu Thin Films: Understanding the Combined Effects of Growth Rate and Grain Size

Abstract

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.

Understanding residual stress in thin films: Analyzing wafer curvature measurements for Ag, Cu, Ni, Fe, Ti, and Cr with a kinetic model

“…The work reported here focuses on evaporation-deposited transition metals, but the mechanisms in the model have also been shown to work for electrodeposited films. 5,8,9,17,52 An extended version of the model that includes energetic (sputter) deposition has been used to analyze the dependence of the stress on the growth rate and sputter-gas pressure (which affects the particle's energy) in Mo, 34 Cu, 53 and Ni. 54 Future studies are planned to look at other published stress measurements in sputter-deposited metal films.…”

“…Consequently, there have been many measurements of stress evolution in thin films. [4][5][6][7][8][9][10][11][12][13][14][15] Many results show that the processing conditions, materials, and microstructural evolutions all play a role in determining stress. The relationship among them is not simple, e.g., the dependence of stress on the growth rate is non-linear.…”

“…It has been used to analyze the dependence on growth rate and grain size in several systems. 5,7,9,17 To further test and refine the model, it would be useful to compare its predictions with a wider range of data. Therefore, in this work, we use the model to analyze other reported studies in the literature for stress evolution in Ag, Cu, Ni, Fe, Ti, and Cr thin films.…”

“…The grain size at the surface affects the stress in the new layers that are created as the film grows. 5 In addition, grain growth within the body of the film can change the stress in layers that have already been deposited. 20,33 In the absence of grain growth, the slope of the stress-thickness reaches a constant slope, which indicates a steady state incremental stress.…”

Effect of processing conditions on residual stress in sputtered transition metal nitrides (TiN, ZrN and TaN): Experiments and modeling

“…L is the grain size in the film which is assumed to remain constant for steady-state conditions. The mechanisms in this model, with the addition of stress from grain growth, have been used to analyze stress in metal films deposited by electrodeposition [35,[39][40][41][42] and evaporation [43,44].…”