Modeling and simulation of atomic layer deposition at the feature scale

We present a transient Boltzmann equation based transport and reaction model for atomic layer deposition (ALD) at the feature scale. The transport model has no adjustable parameters. In this article, we focus on the reaction step and the postreaction purge steps of ALD. The heterogeneous chemistry model consists of reversible adsorption of a reactant on a single site, and irreversible reaction of a second gaseous reactant with the adsorbed reactant. We conduct studies on the effect of the kinetic rate parameter associated with the reaction. We provide results for number densities of gaseous species, fluxes to the surface of the feature, and surface coverage of the adsorbing reactant as functions of time. For reasonable reaction rate parameter values, the time scale for gas transport is much smaller than that for reaction and desorption. For these cases, an analytic expression for the time evolution of the surface coverage of the adsorbing reactant provides a good approximation to the solution obtained from the transport and reaction model. The results show that fractional coverage of the adsorbing reactant reduces significantly in the reaction step due to reaction with the gaseous reactant and desorption. Larger values of the reaction rate parameter lead to larger reductions in the fractional coverage during the reaction step. For smaller values of the reaction rate parameter, the decrease in coverage is dominated by desorption. The surface coverage of the adsorbing reactant also decreases during purge steps, due to desorption.