DEPOSITION AND CRYSTALLIZATION OF A-SI LOW-PRESSURE CHEMICALLY VAPOR-DEPOSITED FILMS OBTAINED BY LOW-TEMPERATURE PYROLYSIS OF DISILANE

In this work we have studied the deposition and crystallization of silicon films initially deposited in the amorphous phase by thermal decomposition of disilane and subsequently crystallized upon a low temperature thermal anneal. Experiments were performed over a wide range of deposition conditions. The grain size of the crystallized films was found to depend upon the deposition conditions; particularly it was found to increase monotonically with increasing deposition rate, while a nonmonotonic behavior was observed with respect to the deposition temperature. For films deposited with similar deposition rates, in the temperature range of 450 to 550-degrees-C, a maximum in the grain size was observed at 470-degrees-C. This maximum is attributed to the minimization of the nucleation rate, observed at 470-degrees-C, combined with the faster crystallite growth rate at low deposition temperatures. The minimum in the nucleation rate is explained by the combination of two mechanisms which, we propose, contribute to the nucleation process. One mechanism is attributed to nucleation induced by the high free energy associated with a highly disordered silicon matrix. The other mechanism is attributed to nucleation occurring on pre-existing subnuclei formations, in a less disordered structure.