Multi-scale modeling of atomic layer deposition

Atomic layer deposition (ALD) of high-K dielectric materials has been investigated using a multi-scale modeling strategy. The computational techniques used in our research include: (1) ab-initio quantum mechanical cluster calculations, (2) periodic density functional theory (DFT) calculations based on tight-binding techniques and (3) all-atom modeling based on molecular dynamics (MD) simulation.;The surface chemistries and initial surface reactions involved in ALD of TiO2 and Al2O3 have been investigated using ab-initio cluster calculations and periodic density functional theory (DFT) calculations. The detailed reaction mechanisms on different types of functional groups of the SiO2 and Si substrates have been proposed.;Using electronic structure calculations, a new oxygen incorporation mechanism is predicted for the atomic layer deposition of Al2O3 from trimethylaluminum (TMA) and H2O. Compared to the isolated H2O + H/Si(100) reaction, the H2O + TMA + H/Si(100) reaction is strongly preferred both kinetically and thermodynamically. This reaction is relevant to the formation of the SiO2 interfacial oxide layer, which is an unwanted feature produced during the deposition process.;All of the investigated initial reactions are predicted to have large rate constants at typical ALD temperatures. In addition, we find the binding energies of the ALD precursors are generally small. These results suggest that adsorption is more likely to be the rate-determining step in the overall ALD dynamics in typical ALD process conditions.;Based on the understanding of ALD from ab-initio calculations, MD-based all-atom simulations were designed to simulate the Al2O 3 ALD process at a larger scale. The evolution of microscopic structures of the Al2O3 films and the influence of operation parameters on the ALD process have been investigated using the all-atom simulations. The densification process has been reproduced with the MD simulations. A starting low surface coverage of --OH groups can lead to an island growth mode, and hence a rough film is generated at the beginning of ALD. Hydroxyl group distribution is also an important factor in ALD, due to steric effects. Temperature can have complex effects on ALD via changing the surface --OH group concentration, the reaction kinetics, and the surface coverage.;Overall, our calculations show that the actual ALD growth mechanism is complicated by competing reactions and significant structural relaxation.