Effect of surface re-emission on the surface roughness of film growth in low pressure chemical vapor deposition

Abstract

For films deposited by low pressure chemical vapor deposition (LPCVD) the effect of roughness in the underlying substrate on film microstructure is investigated by computer simulation. Previous workers have assumed a normal surface velocity related to the local surface curvature; however, transport in many LPCVD systems has been shown to be governed by surface re-emission of the deposition precursors with a single sticking coefficient. In this article, the dependence of film profile evolution on both the sticking coefficient of the precursors, as well as the wave number of the underlying roughness is demonstrated. All wave numbers are shown to grow in the small time regime, for all values of the sticking coefficient except zero. At longer times, the mechanism of cusp formation is shown to arrest this growth for small but finite values of the sticking coefficient. In the limit that the sticking coefficient approaches zero, a simple geometric model for profile evolution is developed to accurately predict both the time required for cusp formation, as well as the maximum rate of decay of roughness. All wave numbers grow for large values of the sticking coefficient, eventually leading to the formation of a columnar microstructure with voids. For the sticking coefficient equal to unity, small geometric perturbations on the starting surface are shown to grow into asymptotic columns. Pair interactions between adjacent, unequal perturbations are studied, and larger columns are found to ‘‘shadow’’ smaller columns. For low values of the sticking coefficient, these interactions result in slowing down the decay of surface roughness by an effective halving of the wave number. The conclusions obtained from simulating deposition on periodic, sinusoidal surfaces are shown to be useful in understanding deposition on statistically rough surfaces.