Unifying model for step coverage in deposition processes for multilevel interconnection

A molecular transport-reaction model based on a pseudosteady approximation of the Boltzmann equation provides a unifying understanding of step coverage phenomena observed for the a spectrum of deposition processes. The model suggests that for all chemically based processes, the reactivity of precursors or intermediates, as characterized by their reactive sticking coefficients, controls step coverage. Classical reaction rate expressions may be used to estimate reactive sticking coefficient dependences on flux; these dependences are directly incorporated in the model to determine the spatial and temporal evolution of the sticking coefficients as the feature fill proceeds. For all but first-order reactions, use of a single value for the sticking coefficient is not warranted. The model is formulated in such a way that physical properties of the films (i.e., density) can be estimated if the property dependence on precursor incident angle is known.