Mechanism and kinetics of thin zirconium and hafnium oxide film growth in an ALD reactor

A mechanism of HfO2 and ZrO2 film growth in an ALD reactor from metal chlorides and water vapor is proposed to explain the experimentally observed features of the process: the formation of less than one monolayer per cycle and the dependence of the film growth rate (mass or thickness increment per cycle) and the residual chorine concentration on the process temperature. Energy parameters of the relevant gas-surface reactions are estimated from quantum-chemical density functional theory calculations. The rate constants of the elementary reactions are calculated using RRKM theory. ALD process simulations, based on the proposed mechanism and a transient plug-flow reactor model, are consistent with the available experimental data, indicating a decrease in deposition rate with increasing temperature. The reduction in deposition rate is attributed to the increased dehydroxylation of the film surface as the temperature is increased. The H2O adsorption energy was found to increase with increasing dehydroxylation from 33 to 53 kcal/mol for ZrO2 and from 35 to 51 kcal/mol for HfO2. A kinetic Monte Carlo model of film growth, based on the proposed mechanism, describes the observed temperature dependence of the residual chlorine concentration in the film in terms of the steric repulsion between chemisorbed surface groups and adsorbed MCl4 molecules (M=Zr, Hf).