The results of Monte Carlo computer simulations of near-surface mass transport of the gas-phase species within three dimensional structures, such as via holes and trenches on the wafer surface, in the context of low-pressure chemical vapor deposition (LPCVD) are presented. Issues treated include: (i) step coverage of deposited films, (ii) the relative importance of surface mobility vs. re-emission of adsorbed reaction precursors at the surface in achieving conformal coverage in a chemical vapor deposition (CVD) process, and (iii) the effective pressure of byproduct within via holes during selective