Ballistic transport‐reaction prediction of film conformality in tetraethoxysilane O2 plasma enhanced deposition of silicon dioxide

Abstract

EVOLVE, a low pressure deposition process simulator based on a fundamental model for free molecular transport and heterogeneous surface reactions in features, is used to predict the evolution of silicon dioxide film profiles during plasma enhanced chemical vapor deposition from mixtures of tetraethoxysilane (TEOS) and oxygen. The constitutive relationships required by EVOLVE are supplied by simple models for the plasma, the plasma sheath and the surface chemistry. The intrinsic kinetic model used in the simulations involves film growth by oxidative attack on adsorbed TEOS and/or TEOS fragments by both oxygen ions and oxygen atoms. Recombination of oxygen atoms on the surface of the growing film competes with TEOS oxidation by atoms. The plasma models are used to predict the fluxes of oxygen ions and oxygen atoms to the surface. The fluxes of all neutral species from the source and from all surfaces are assumed to obey cosine distribution functions. Oxygen ions are assumed to follow an exponential distribution; the standard deviation of the distribution is adjusted to match predicted film profiles with experimentally determined profiles. This combination of an almost directional component and an almost isotropic component allows the prediction of the experimental trends in deposition rate and film conformality with operating conditions. The constitutive models are used by EVOLVE to predict film profiles as a function of temperature, within their window of validity, for deposition in ideal rectangular trenches with an aspect ratio of 2. Film conformality decreases as temperature increases, even though deposition rate actually decreases. Film conformality decreases with increasing pressure and increases with increasing power. All of these predicted trends in conformality agree with our experimental results.