The deposition of epitaxial thin solid films of Si from chlorosilanes was investigated using a multiscale approach. Gas phase and surface kinetic schemes were developed using kinetic constants that, when not found in the literature, were calculated using density functional and transition state theory. Temperature fields, velocity profiles and mass transport rates inside the deposition reactor were calculated solving mass, momentum and energy conservation equations in two dimensions. Finally, the morphology evolution of the film was investigated with three-dimensional Kinetic Monte Carlo. Diffusion parameters of adsorbed Cl atoms were calculated with density functional theory representing the surface as clusters. The results of the simulations show that the surface chemistry might be more complicated than expected. The calculated presence of a significant concentration of islands and rough terrace steps is in fact likely to influence the HCl desorption kinetics, which appears now to be not consistent with experimental data.