Mound formation in surface growth under shadowing

Abstract

In this paper we report on the morphological evolution of thin films grown by commonly employed deposition techniques, such as sputtering and chemical vapor deposition. In these deposition techniques, an angular distribution of incident particle flux leads to the shadowing effect, which often plays an important role in defining the growth front morphology. We show both by simulations and experiments that a mounded structure can be formed with a characteristic length scale, or ``wavelength'' $\ensuremath{\lambda}$, which describes the separation of the mounds. We also show that the temporal evolution of $\ensuremath{\lambda}$ is distinctly different from that of the mound size or lateral correlation length $\ensuremath{\xi}$. The wavelength grows as a function of time in a power-law form, $\ensuremath{\lambda}\ensuremath{\sim}{t}^{p}$, where $p\ensuremath{\approx}0.5$ for a wide range of growth conditions, while the mound size grows as $\ensuremath{\xi}\ensuremath{\sim}{t}^{1∕z}$, where $1∕z$ varies depending on growth conditions. The existence of these two length scales and their different growth rates leads to a breakdown of the self-affine and dynamic scaling hypotheses that have been used to describe many surface growth phenomena in the past.