Simple model for atomic layer deposition precursor reaction and transport in a viscous-flow tubular reactor

Precursor reaction and transport are both critical in determining the thickness uniformity and conformality of atomic layer deposition (ALD) thin films. However, it is sometimes difficult to predict how changes in conditions, such as mass flow rate or precursor reactivity, will affect the outcome of an ALD experiment. To provide some insight and guidance, we have developed a simple 1D model to describe precursor transport and reaction in a tubular viscous flow ALD reactor. After making some simplifying assumptions, we show that the transport problem depends only on three independent parameters, the Peclet number, the Damkoeler number, and the excess number, which can be easily calculated for most ALD processes. Despite its simplicity, we obtain very good agreement with experimental results for the thickness profiles of ALD Al2O3 films deposited using trimethyl aluminum and H2O. The authors have applied the model to study the impact of precursor properties and experimental conditions on the growth profiles and saturation curves obtained during ALD, including the presence of nonself-limited wall recombination.