We present a systematic approach to formulating chemical mechanisms to chemical vapor deposition processes with the unusually large growth rate enhancement observed for in situ B doping of Si as a case study. The basic computational tools needed for mechanism development: quantum chemistry calculations, sensitivity analysis, and finite element simulations are combined to develop a mechanism for the process and to provide quantitative predictions of observed growth and dopant incorporation rates. Ab initio quantum chemistry computations of small molecules and clusters relevant to the H-B-Cl-Si system are used to determine thermodynamic and kinetics parameters. Particular emphasis is given to CI-H exchange reactions between borane and chlorosilanes, which are shown to proceed with low reaction barriers. The reaction mechanism is incorporated into finite element simulation of reported deposition data. The developed mechanism is capable of representing quantitatively: (a) the silicon deposition from dichlorosilane; (b) etching of silicon by HCl; and (c) B-doped Si deposition in the SiCl2H2/B2H6/H-2 deposition system. The most important deposition processes are identified by sensitivity analysis, and gas-phase decomposition reactions of dichlorosilane are shown to be insignificant in the deposition process.