PREPARATION OF MICROCRYSTALLINE SILICON FILMS BY VERY-HIGH-FREQUENCY DIGITAL CHEMICAL VAPOR-DEPOSITION

A novel method of growing microcrystalline silicon, called "VHF digital CVD", which consists of five steps, (i) nuclear formation, (ii) a-Si deposition, (iii) annealing for crystallization, (iv) grain boundary passivation, and (v) grain size limitation, is proposed. Microcrystalline silicon films have been fabricated by repeating step (ii) with VHF plasma-enhanced CVD using a gaseous mixture of SiH4 and H-2, and step (iii) with hydrogen plasma. These films have been characterized by means of Raman spectroscopy, X-ray diffraction, infrared absorption, dark- and photo-conductivity, and transmission electron microscopy. We discuss the transformation of the structure from amorphous to microcrystalline in connection with annealing time, film thickness, and deposition temperature. The diffusion of hydrogen radicals is the rate-limiting process for crystallization.