Reactant utilization in CVD and ALD chambers

In both chemical vapor deposition (CVD) and atomic layer deposition (ALD) reactors, a substantial fraction of the reactants never react at the substrate and are pumped away. To quantify this, an analytic expression for reactant utilization is derived for an axisymmetric stagnation flow reactor. The utilization is found to depend on the dimensionless Peclet and Damkohler numbers. The highest utilization is seen for CVD processes in the mass transfer limit (Da → ∞). For finite reaction rates, CVD processes always have higher utilization than ALD processes.