A multicomponent mathematical model incorporating simultaneous Knudsen diffusion and heterogeneous reaction in a feature of arbitrary geometry has been developed to quantitatively predict step coverage in LPCVD. The single component model reveals that for a given CVD chemistry and feature geometry, deposition uniformity is controlled by a single parameter called the step coverage modulus. In multicomponent systems, each additional reactant partial pressure dependence in the deposition rate expression introduces an additional parameter equal to the ratio of the initial reactant partial pressures. Manipulation of the instantaneous step coverage modulus, through time variations of temperature and/or pressure results in higher average film growth rates without incurring a penalty in step coverage over patterned regions of the wafer. For deposition of SiO2 from TEOS, the step coverage modulus is varied through a time dependent temperature path. The path is chosen by constraining the deposition rate in the feature such that it varies by less than a few percent from top to bottom. For deposition of SiO2 from SiH4/O2, silane partial pressure is varied since the reaction rate is relatively insensitive to temperature. In each case. time savings of approximately 50% are achieved.