A detailed study of the kinetics of Si film growth from disilane has been undertaken. In order to understand the growth kinetics at the atomic level, the mechanisms of disilane decomposition on Si(111) surfaces have been studied using modulated molecular beam scattering (MMBS) combined with surface science techniques: static secondary ion mass spectrometry (SIMS), temperature programmed desorption (TPD), and low-energy electron diffraction (LEED).1Modulated molecular beam spectrometry was performed over the temperature range of 50–850 °C and with beam fluxes from 1015 to 1016 cm−2 s 1−2. Rapid evolution of monosilane above 500 °C and unusually slow desorption of H2(time constant ≈1s at 850 °C) is observed. We have modeled the MMBS data using reaction mechanisms derived experimentally. According to this model, adsorbed disilane decomposes producing SiH4 and chemisorbed SiH. Disilane also reacts with the chemisorbed SiH and emits SiH4 which is the main path for hydrogen removal from the surface. The SiH migrates by random ‘”exploration” to ledge sites on the surface forming *SiH. The less significant path of surface hydrogen removal is the recombination of two *SiH desorbing H2. © 1990, American Vacuum Society. All rights reserved.