Mechanisms Controlling Preferred Orientation of Chemical Vapour Deposited Polycrystalline Films

In the absence of epitaxy between a film and a substrate, the preferred orientation of poly crystal line films can often be explained by the "evolutionary selection rule", which states that grains with the fastest growing direction normal to the substrate envelope the other grains and determine the final orientation of the film. However, the mechanism determining the fastest growing plane and the factors affecting the growth rates of each plane are still not well understood. We examined existing experimental results in the previous literatures and found a correlation between process conditions and preferred orientation for poly-Si and poly-SiC thin films. We present a model based on Langmuir-type adsorption for predicting preferred orientation, which agrees well with experimental results in the previous literatures for Si and SiC.