We demonstrate a competitive co-diffusion enhanced CVD concept for conformal film deposition by using Xe as an inert diffusion additive in CVD of boron carbide from the single source precursor TEB. Our results show an increase in the step coverage from 0.71 to 0.97 in 10:1 aspect ratio feature when Xe was added to the process. At present, the exact mechanism for this increase in SC is not understood in detail. We suggest that possible mechanisms could be that the heavier Xe atoms enhances the diffusion of the lighter precursor molecules by competitive co-diffusion, and that the heavy Xe atoms reduces the surface residence time by enhancing desorption rate for reactive intermediates by surface collisions. Further experimental and modelling studies are needed to fully determine the mechanism, which could also be a combination of at least these. The elemental composition, chemical environments, and density of the films were not significantly affected by the addition of Xe gas. The concept was further demonstrated by deposition in lateral high aspect ratio structures where the film deposition corresponded to conformal film in at least a 50:1 aspect ratio feature. We foresee that this competitive co-diffusion approach can improve conformality in many CVD processes.