A physically based model of atomic layer deposition (ALD) surface reaction dynamics is developed and applied to alumina ALD with water and trimethylaluminum precursors. The time-dependent growth surface composition is modeled by computing the equilibrium precursor adduct surface concentrations during each half-reaction and the rate constants of the ligand exchange reactions using transition state theory. To describe the continuous cyclic operation of the deposition reaction system, a numerical procedure to discretize limit-cycle solutions is developed and used to distinguish saturating growth per cycle (GPC) from non-saturating (gpc) conditions. The transition between the two regimes is studied as a function of precursor partial pressure, exposure time, and temperature.
A laboratory-scale atomic layer deposition (ALD) reactor system model is derived for alumina deposition using trimethylaluminum and water as precursors. Model components describing the precursor thermophysical properties, reactor-scale gas-phase dynamics and surface reaction kinetics derived from absolute reaction rate theory are integrated to simulate the complete reactor system. Limit-cycle solutions defining continuous cyclic ALD reactor operation are computed with a fixed point algorithm based on collocation discretization in time, resulting in an unambiguous definition of film growth-per-cycle (gpc). A key finding of this study is that unintended chemical vapor deposition conditions can mask regions of operation that would otherwise correspond to ideal saturating ALD operation. The use of the simulator for assisting in process design decisions is presented.
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