Direct Evidence for Effects of Grain Structure on Reversible Compressive Deposition Stresses in Polycrystalline Gold Films

Abstract

A component of the compressive stress that develops during deposition of polycrystalline thin films reversibly changes during interruptions of growth. The mechanism responsible for this phenomenon has been the subject of much recent speculation and experimental work. In this Letter, we have varied the inplane grain size of columnar polycrystalline gold films with a fixed thickness, by varying their thermal history. Without a vacuum break, the stress in these films was then measured in situ during growth and during interruptions in growth. Homoepitaxial gold films were similarly characterized as part of this study. The inverse of the in-plane grain size and the corresponding reversible stress change were found to be proportional, with zero reversible stress change observed for infinite grain size (homoepitaxial films). These results demonstrate a clear role of grain size in the reversible changes in gold films.

Compressive intrinsic stress originates in the grain boundaries of dense refractory polycrystalline thin films

“…These mechanisms result to the same net effect (i.e., incorporation of atoms into grain boundaries) as those that have been suggested to be active when deposition conditions allow for fast, thermally activated surface diffusion, 20,21 e.g., during growth of low melting point metallic films at room temperature. The compressive stress originating in the grain boundaries of the film provides a driving force for out-diffusion of atoms from the grain boundaries and thereby implies that part of the stress relaxation upon deposition interruption is caused by outdiffusion of atoms from the grain boundaries if kinetic conditions favor atom diffusion, 20,21,49 although it is likely not the sole cause of these relaxations. 24,[50][51][52][53]…”

Correlation of shape changes of grain surfaces and reversible stress evolution during interruptions of polycrystalline film growth

“…8 Understanding the mechanisms for this complex stress evolution has been the focus of much recent research. [13][14][15][16][17] Most recently, the stress evolution during a growth interruption has been shown to involve multiple kinetic processes, which can be interpreted as a fast reversible process and a slow irreversible process. 18 The slow process was shown to correspond to a process occurring in the bulk of the film and can be attributed mostly to grain growth after deposition.…”

Atom insertion into grain boundaries and stress generation in physically vapor deposited films

“…12 On the other hand, when deposition is performed at relatively high T s /T m (typically above 0.2), adatoms have sufficient mobility for dense films to form, 12 which is accompanied by generation of a compressive growth stress after formation of a continuous film. 1,4,10 This phenomenon has been explained based on results from in situ monitoring of intrinsic stress evolution during and after deposition, growth simulations, and analytical models 8,9,[13][14][15][16][17] to be the effect of diffusion of adatoms into grain boundaries driven by a chemical potential difference between the latter and the film surface. 8,9 However, direct experimental evidence for insertion of film forming species into grain boundaries is not available in the literature, since this would require observation of atoms exiting grain boundaries after deposition is ceased.…”