Predictive modeling of atomic layer deposition on the feature scale

A feature scale simulator for atomic layer deposition (ALD) is presented that combines a Boltzmann equation transport model with chemistry models. A simple but instructive chemistry is considered; one reactant species adsorbs onto the surface, and a second reactant reacts with it from the gas phase (Eley-Rideal). This work includes potential desorption of the adsorbed species during purge steps, which may or may not play a role in any given ALD system. Three sets (cases) of rate parameters are chosen to compare chemical rates with transport rates. The duration of the ALD pulses and the geometry of the representative feature are the same for each case. Simulation results are presented for all four steps in one ALD cycle, adsorption, post-adsorption purge, reaction, and post-reaction purge. The results are extended to multiple ALD cycles, and the monolayers per cycle are estimated. We highlight the potential trade-off between pulse durations and deposition rate (wafer throughput) e.g. the time penalty required to increase the amount adsorbed during the adsorption step. The simulation methodology we present can be used to determine the pulse durations that maximize throughput for a given chemistry and chemical rate parameters. One overall observation is that transport is fast relative to chemical reactions, for reasonable kinetic parameters. (C) 2002 Elsevier Science B.V. All rights reserved.