Diffusion, heat transfer, equilibrium molecular density and kinetic mechanism of morphological instability in physical vapor deposition

Abstract

The growth interface stability in physical vapor deposition processes has been investigated. It is shown that in addition to (i) the gradient of the deposited substance in front of the growth interface, there are other reasons of the destabilization: (ii) the dependence of the kinetic coefficient on temperature, (iii) the dependence of the equilibrium molecular density (pressure) of the depositing substance on temperature and (iv) the temperature gradient across the deposited layer associated with the released sublimation heat and applied heat transfer conditions. The stability of the interface is shown to be determined by the interplay of these four effects together with the surface free energy depending on the local curvature. The breakdown of the morphological stability of the interface is shown to be possible even under a zero gradient of the molecular density of the deposited substance due to the interplay of kinetic coefficient and equilibrium molecular density perturbed in a temperature gradient. It is shown that the following transitions of growth modes can occur with increase of the layer thickness: (i) instability/stability, (ii) stability/instability and (iii) instability/stability/instability.