Fast and slow stress evolution mechanisms during interruptions of Volmer-Weber growth

Abstract

The evolution of mechanical stress during Volmer-Weber growth of thin films is complex, often including a reversible stress evolution during interruptions of film deposition. The underlying mechanism for stress evolution during growth interruptions has been extensively debated, but remains unclear. In this work, in situ measurements of stress evolution during growth interruptions of various time scales, film thicknesses, and substrate temperatures were made during deposition of gold and nickel films. It was found that at least two mechanisms lead to the observed stress evolution, one fast (time constant ∼102 s) and one slow (time constant ∼104 s). The fast process is reversible and weakly dependent on the film thickness, while the slow process is irreversible and strongly dependent on the film thickness. It is shown that grain growth during growth interruptions can account for a significant portion of the stress change associated with the slow process. The fast reversible process is likely to be associated with reversible changes of the surface structure.

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

“…5,11,18 Although the exact mechanism for the fast reversible stress evolution has not been identified, a few important features are suggested by previous experimental observations. 7,9,13,15,18 (1) The mechanism leads to "reversible stress evolution" during a growth interruption and upon resumption. That is, as the growth is resumed, the stress rapidly returns to the pre-interruption stress evolution trajectory and continues as if the growth had never been stopped.…”

“…[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. 5,11,18 Although the exact mechanism for the fast reversible stress evolution has not been identified, a few important features are suggested by previous experimental observations.…”

“…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. 5,11,18 Although the exact mechanism for the fast reversible stress evolution has not been identified, a few important features are suggested by previous experimental observations. 7,9,13,15,18 (1) The mechanism leads to "reversible stress evolution" during a growth interruption and upon resumption.…”

“…The details of this technique have been discussed elsewhere. 18,19 The evolution of surface structure during growth interruptions was characterized using atomic force microscopy (AFM). AFM imaging was carried out in tapping mode using a Veeco Nanoscope IV AFM with RTESP silicon probes (normal frequency 300 kHz, tip radius 8 nm).…”

Atomistic view on thin film nucleation and growth by using highly ionized and pulsed vapour fluxes

“…The stress relaxation was then argued to be the effect of out-diffusion of atoms from grain boundaries due to a reversal of the chemical potential difference when deposition is interrupted [77,78,95]. Experimental studies have reported that the stress relaxation upon interruption scales with the inverse grain size as predicted by the out-diffusion model [96] but that the stress relaxation does not have the temperature dependence predicted by a diffusion based relaxation process [97,98]. Others have suggested [81,99] that grain rotation coupled with grain boundary diffusion as a cause of the stress relaxation.…”