Influence of surface-activated reaction kinetics on low-pressure chemical vapor deposition conformality over micro features

Abstract

The coupled effect of molecular scattering and surface-activated reactions on low-pressure chemical vapor deposition (LPCVD) film conformality is investigated. Using a single-precursor two-step surface-activated deposition as an example, film conformality can be found to depend on two first-principle dimensionless parameters-Sc, the intrinsic sticking coefficient, and Sa, the surface saturation factor. An analytical integral material balance formulation, developed for the feature-scale molecular transport, is solved numerically in a wide range of Sc and Sa. The results show that film conformality generally improves with decreasing Sc and increasing Sa. With Sc fixed in most LPCVD processes (due to the nature of the precursor species), the ability to control Sa in the process becomes the key to conformal deposition. The intrinsic surface-activated deposition rate expression shows no apparent reaction order. Therefore, previously reported Monte Carlo schemes and integral-differential models employing a single sticking parameter or a fixed reaction order to characterize LPCVD step coverage behavior are applicable only in limited cases. The two-parameter model has been found useful in understanding the H2-reduced tungsten CVD process, for which the first-principle parameters can be determined from kinetic data reported in the literature. © 1993, American Vacuum Society. All rights reserved.