We use density functional theory to investigate the chemical vapor deposition of (100) silicon front silane. The reaction proceeds through four sequential steps. The first step is activation of surface sites through hydrogen abstractions by atomic H or through H-2 desorption. We find that hydrogen abstraction barriers by atomic H are less than 1 kcal/mol while H-2 desorption proceeds through a two-step pathway with an overall barrier of 61.1 kcal/mol. Next, adsorption of SiH4 onto bare dimer sites occurs. We calculate the B3LYP barrier to SiH4 adsorption on a single dimer to be 7.4 kcal/mol while the barrier across two dimers is 14.3 kcal/mol. Then, adsorbed SiH3 transforms to bridged SiH2(a) with a barrier of 5.7 kcal/mol relative to SiH3(a) for the mechanism requiring H(g) while the barrier for the mechanism requiring no H(g) is 32.9 kcal/mol. where (g) and (a) represent gas and adsorbed species, respectively. Finally, the dihydride surface transforms to the monohydride surface through two-sequential steps with an overall barrier of 47.0 kcal/mol. which agrees well with the TPD barrier of 43 kcal/mol. The B3LYP H-2 desorption barrier of 61.1 kcal/mol and SiH4 adsorption barrier of 7.4 kcal/mol are in good agreement with the TPD values of 57.2 to 58 kcal/mol and 3.3 to 4.0 kcal/mol, respectively.