Simulation of growth dynamics in atomic layer deposition. Part III. Polycrystalline films from tetragonal crystallites

Materials with one- and two-dimensional crystal structures often form crystals with the shape of needles and platelets, respectively. This should be expected to have great influence on the properties of thin films grown from such materials, and the effect on texture and topography is shown in this paper by a series of simulations. The topic of this paper is the effect of different aspect ratios of crystals with tetragonal symmetry on the resulting thin films. However the major results should also apply to crystals of other types of symmetry having aspect ratios deviating from one. The growth dynamics in atomic layer deposition of polycrystalline thin films have been simulated for randomly oriented and randomly positioned crystallites. Crystalline seed objects adapting shapes of tetragonal boxes with aspect ratios from 0.1 (platelets) to 10 (needles) has been used as examples for growth of films from tetragonal crystals. The dependence of roughness, surface crystal density, and texture on the film thickness is shown. Topography and cross sections of simulated films with different aspect ratios are discussed. Non-linear growth regimes are consistently found in the initial stage of the film formation. A conversion from type-2 to type-1 substrate inhibited growth is observed as the aspect ratio deviates significantly from one.