How to control solid state dewetting: A short review

Abstract

In the past decade there have been many theoretical and experimental efforts to study the mechanisms of solid state dewetting, that means the spontaneous agglomeration of a thin solid film on a substrate into an assembly of 3D islands. The dewetting studies of solid films on solid substrates have not yet reached the degree of maturity achieved for liquids but there is now enough experimental data to consider the possibility of a future “dewetting engineering”. By dewetting engineering we mean all the ways to tune and/or control the kinetics of dewetting as well as the morphology of the final dewetted state. The ultimate goal is to avoid dewetting when it complicates the fabrication of thin film-based devices or to use it for the spontaneous production of an assembly of nanoscaled islands on solid substrates.

For this purpose we review the different parameters that influence the dewetting then illustrate how the dewetted state may be tuned by varying the thickness of the film, the annealing temperature, or the state of strain in the film. Moreover, adsorbed or absorbed species (by deposition or ionic impingement/ion bombardment) may modify the surface properties of the film or the mobility properties of the contact line film/substrate and thus the dewetting properties. Anisotropic properties of the film may also be used to initiate the dewetting from perfectly oriented edge fronts, leading to highly ordered 3D islands. New approaches using substrate pre-patterning or film patterning are very promising to achieve the dewetting engineering.

Ideal systems for studying solid state dewetting are single crystalline films deposited or bonded on amorphous substrates, so that, among the numerous dewetting systems reported in the literature, ultra-thin crystalline silicon-on-insulator (SOI) film (a Si film bonded on an amorphous SiO₂ substrate) is considered as a model system for studying how to control solid state dewetting. Other systems, as Ni epitaxially grown on MgO, are also used to illustrate the different approaches for a “dewetting engineering”.