Competitive co-diffusion as a route to enhanced step coverage in chemical vapor deposition

Molecules with a lower mass diffuse faster than heavier molecules in a mixture of gases at local thermodynamic equilibrium. We hypothesize that this phenomenon can be used to improve film uniformity and step coverage in chemical vapor deposition (CVD). Our concept is to add a heavy inert molecule as a diffusion additive to enhance the diffusion of the reactive gas species. We verify this by adding a co-flow of Xe in a thermal CVD process for boron carbide using a single source precursor. When adding a co-flow of Xe to the process we noted an increase in step coverage from 0.71 to 0.97 at 550 °C in 10:1 aspect ratio feature. The concept was further validated by depositing in lateral high aspect ratio chips with 500 nm gap height, rendering a penetration depth of about 25 μm with maintained material homogeneity into the structure. The results show that competitive co-diffusion with a heavy inert gas is a viable route to conformal CVD films.