Intrinsic compressive stress in polycrystalline films with negligible grain boundary diffusion

Abstract

The model developed here describes compressive stress evolution during the growth of continuous, polycrystalline films ͑i.e., beyond the point where individual islands have coalesced into a continuous film͒. These stresses are attributed to the insertion of excess adatoms at grain boundaries. Steady state occurs when the strain energy at the top of the film is balanced by the local excess chemical potential of surface adatmos. Strain gradients associated with this compressive stress mechanism depend on the kinetics of the process. In the absence of grain boundary diffusion, these strain profiles are determined by the ratio of the atom insertion and growth rates. The steady-state strain and the strain evolution kinetics also depend on the two key length scales, the grain size, and the film thickness. The ratio of these two lengths ͑i.e., the grain aspect ratio͒ can also have a significant influence on the thermodynamic driving force for strain evolution if the grain sizes are sufficiently small. The model is fit to existing data for the growth of AlN films. However, more detailed comparisons will require experiments that are specifically designed to test this model.

Dislocation bending and tensile stress generation in GaN and AlGaN films

“…A quantitative kinetic model is then developed to explain the resulting evolution of growth stress due to dislocation bending and interaction with thickness. This is based on a kinetic model that was first proposed by Chason et al [3] and Sheldon et al [4]. It was then adapted [5] to correlate dislocation bending and stress evolution in AlGaN films under compression, in which the microstructural evolution only involved dislocation bending with little interaction or density reduction.…”

Novel in situ mechanical testers to enable integrated metal surface micro-machines.

“…A similar process occurs when Ni atoms are trapped interstitially, or at low coordination sites such as a grain boundary or interstitially in a Ni film. The literature has established two possible mechanisms by which the incorporation of atoms into low coordination sites creating compressive stress is possible: kinetic trapping [32] and adatom trapping at grain-boundaries [33]. Though there is currently no definitive evidence that these mechanisms are active during thin film growth, there is evidence that indicates that they are highly plausible [33,34].…”

“…The literature has established two possible mechanisms by which the incorporation of atoms into low coordination sites creating compressive stress is possible: kinetic trapping [32] and adatom trapping at grain-boundaries [33]. Though there is currently no definitive evidence that these mechanisms are active during thin film growth, there is evidence that indicates that they are highly plausible [33,34]. Therefore, we believe that it is beneficial to evaluate them as possible sources for the steady-state stress observed during electrodeposition of Ni from a sulfamate-based bath.…”

“…al [33]. The initial work examined the case where diffusion of the adatoms was allowed within the grain boundary, which was predicted to cause a compressive growth stress that was reversed during an interruption of the deposition [33].…”

“…coalescing steps edges or grain boundary, can result in a driving force for diffusion of adatoms into the trapping site [34]. Chason et al [33] proposed that such a driving force results from the presence of adatoms on the free-surface during deposition and that the super-saturation induced by the presence of these adatoms is only weakly dependent on deposition. As a result, increasing the deposition rate causes the grain boundary area to increase faster than the adatom supply, so that higher rates lead to lower compressive stress.…”