A study was performed using a combination of in-situ real time ellipsometry and atomic force microscopy (AFM) to follow the RTCVD process in real time and measure key nucleation parameters in an effort to elucidate the mechanism of Si nucleation on SiO2. Real time ellipsometry data, in terms of delta versus time, showed significant changes as the deposition evolves from critical nuclei through coalescence to continuous film growth thereby allowing. process monitoring and control. From the AFM images, nuclei parameters such as nuclei height, radius, and density were collected and compared across processing temperatures. It was found that kinetic factors control the growth process resulting in a transition temperature (660°C) where the size, shape, and density of the nuclei abruptly changes from small numerous nuclei to large, sparse disk-like nuclei.