Atomic Layer Deposition of Hafnium Oxide from Hafnium Chloride and Water

Abstract

Hafnium oxide (HfO2) is a leading candidate to replace silicon oxide as the gate dielectric for future generation metal-oxide-semiconductor based nanoelectronic devices. Atomic layer deposition (ALD) has recently gained interest because of its suitability for fabrication of conformal films with thicknesses in the nanometer range. This study uses periodic density functional theory (DFT) to investigate the mechanisms of both half-reactions occurring on the growing surface during the ALD of HfO2 using HfCl4 and water as precursors. We find that the adsorption energy and the preferred site of adsorption of the metal precursor are strong functions of the water coverage. As water coverage increases, the metal precursor preferentially interacts with multiple surface adsorption sites. During the water pulse the removal of Cl can be facilitated by either a ligand exchange reaction or the dissociation of Cl upon increase in coordination of the Hf atom of the precursor. Our predicted potential energy surface indicates that a more likely mechanism is hydration of the adsorbed Hf complex up to a coordination number of 7, followed by the dissociation of a chloride ion that is stabilized by solvation. Born-Oppenheimer molecular dynamics (BOMD) simulations of an adsorbed metal precursor in the presence of a multilayer of water shows that Cl dissociation is facile if sufficient water molecules are present to solvate the Cl(-) anions. Hence, solvation plays a crucial role during the water pulse and provides an alternative explanation for why ALD growth rates for this system decrease at high temperatures.

Multiple Proton Diffusion and Film Densification in Atomic Layer Deposition Modeled by Density Functional Theory

“…5,6 The effect of under-coordinated surface oxygen and hydroxyl groups (as the active sites) on the hafnium of adsorbing precursor was inspected and it was shown that the dissociation of HCl is facilitated via increasing the c.n of hafnium during the water pulse. 7 The ALD reactions for elimination of HCl from HfCl 4 are computed to be endothermic 5,7 which is in sharp contrast to the success of this precursor in ALD experiments. In the cluster model the neglect of undercoordinated atoms 6 might cause this discrepancy, while in the slab model the neglected change in entropy 7 might be the cause.…”

Cooperation between adsorbates accounts for the activation of atomic layer deposition reactions

“…So far, the overall computed ALD reactions from halide precursors have been reported in the literature to be endothermic. 21 In other words, no intrinsic driving force for the steps of the growth reaction has been discovered yet. As reported before, adsorption of the hafnium chloride precursor is energetically favorable and a dative chemical bond between the hafnium of the adsorbing HfCl 4 precursor and a surface oxygen atom is created.…”

First-principles molecular dynamics simulations at solid-liquid interfaces with a continuum solvent

“…The realization of liquid phase DFT simulations is therefore a much pursued objective-especially when many of the standard x-ray techniques such as XPS or SAXS are unsuited to provide atomic scale information in solutionbut the inclusion of the solvent considerably increases the cost of first-principles calculations of periodic surfaces and is therefore a rather uncommon practice. 5 In an explicit solvation approach, the vacuum space in the simulation box is filled with solvent molecules. The subsequent growth in the size of the system is in part responsible for the increased computational expense, but more importantly, there is the fact that a static picture is a very poor representation of the liquid state.…”