Fine crystalline grain model for the determination of the morphology of ultrathin amorphous silicon films

Abstract

To obtain the morphology of ultrathin hydrogenated amorphous silicon (a-Si:H) films with thicknesses of 2–10 nm grown by thermal chemical-vapor deposition, we have utilized spectroscopic ellipsometry and introduced a model, called the fine crystalline grain model. This model resolves that the growth of the amorphous silicon matrix starts with the formation of dense deformed crystallites or paracrystallites. A better fit to the experimental data has been obtained with this model when the a-Si:H film thickness is below 20 nm. The fine grain component gradually decreases with the film growth. It has been clarified that the presence of deformed crystallites in the starting a-Si:H films acts as a constraint for their crystallization by rapid thermal annealing.