Nucleation and growth process of nanocrystalline silicon (nc-Si) formed by radio frequency (RF) sputtering method and subsequently thermal treatment has been studied by using high resolution-transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) methods. Silicon (Si) atoms in amorphous sub-oxide (a-SiOx) film were coagulated to form nc-Si with diameter of approximately 1.5 nm in the film after annealing at 900 degreesC. The size and number of nc-Si increased with the increase of the annealing temperature. The average size of nc-Si observed at annealing temperature of 1100 degreesC was 2.5 nm. We also observed nc-Si with high pressure phase in the annealed sample. (C) 2003 Elsevier Science B.V. All rights reserved.