The microstructural and stress evolution in sputter deposited Ni thin films

We report the stress and microstructural evolution for a series of Ni thin films sputter deposited over a range of rates (0.076 and 0.250 nm/s), pressures (0.27, 0.67 and 1.33 Pa), and substrate temperatures (ambient, 100, and 200 degrees C). In general, as the sputtering pressure increased, the stress-thickness product, measured by wafer curvature, became tensile and trended with an increase in pressure regardless of the deposition rate. However, at the lowest sputtering rate and highest substrate temperature, the films exhibited a compressive growth stress. The collective data was then fitted to a kinetic model that accounts for the stress generation at the grain boundaries, from grain growth, and from the creation of defects within the film. The model's predicted fitted parameters matched well to the experimental measurements except for films deposited at the lowest deposition pressure. These particular films exhibited a bimodal grain size distribution which could not be accommodated by the model's use of a singular grain diameter. Nevertheless, in monomodal grain sizes, the results do provide support for the kinetic model in helping to ascertain the various contributing factors for the intrinsic stress development and their microstructural relationship in context to the Thornton zonal morphology descriptors for thin films and coatings.