(159f) Dft Calculations of the Atomic Layer Deposition Growth Mechanisms of High-K Gate Dielectric Oxides

The continuous scaling of metal-oxide-semiconductor field effect transistor (MOSFET) is reducing SiO₂ layer thickness to the limit where leakage current, due to a quantum mechanical tunneling mechanism, becomes a critical problem. Therefore, it is necessary to develop high-k gate dielectric replacement materials for SiO₂ and new deposition methods for new dielectric materials. Among the possible fabrication technologies, atomic layer deposition (ALD) is an ideal candidate, which enables the deposition of a material through highly uniform and conformal growth, with thickness control at the atomic level. Our current work involves the use of a multi-scale modeling strategy to gain theoretical insights into ALD at the atomic scale, which can provide a better understanding of experimental results and accurate predictions of specific properties of the thin films deposited by ALD. The three different levels of computational methods used in our research include: (1) Ab-initio density functional theory (DFT) cluster calculations (2) Periodic DFT calculations based on tight-binding techniques (3) force-field simulations (Molecular dynamics and Kinetic Monte Carlo simulations). These techniques enable us to predict macroscopic behaviors of the ALD process, while preserving the atomic scale details of the system obtained from first principles. In this work, we present results from the first two phases of our simulation strategy, which involves DFT cluster and periodic slab calculations of the ALD film growth mechanisms. A series of cluster calculations are carried out to study the atomistic mechanism and energetics of the initial surface reactions for TiO₂ ALD. The effects of surface functionalities and precursors (TiCl₄ and TiI₄) on the thin film deposition process are discussed. Our calculations show that the concentration and arrangement of the different surface reactive groups determine the resulting film growth characteristics. Therefore, the factors which are related to the presence of the different surface reactive groups, such as the preparation of the initial SiO₂ substrate and the growth temperature, are predicted to have a marked influence on film structure and growth rate. In addition, the temperature dependence of the film growth is discussed through the rate constants calculated by transition state theory. Using periodic DFT calculations, we investigate the interface between the high-k oxides and the silicon substrate. The aggregation mechanism during the ALD process is studied using a supercell. Also, the steric hindrance effects on surface adsorption and reactions are explored. These periodic DFT calculations enable us to study the surface and the reaction mechanisms and energetics in the high coverage limit, which will be used in our future kinetic Monte Carlo simulations.