title: Modeling and in Situ Probing of Surface Reactions in Atomic Layer Deposition.
abstract: Atomic layer deposition (ALD) has matured into a preeminent thin film deposition technique by offering a highly scalable and economic route to integrate chemically dissimilar materials with excellent thickness control down to the subnanometer regime. Contrary to its extensive applications, a quantitative and comprehensive understanding of the reaction processes seems intangible. Complex and manifold reaction pathways are possible, which are strongly affected by the surface chemical state. Here, we report a combined modeling and experimental approach utilizing ReaxFF reactive force field simulation and in situ real-time spectroscopic ellipsometry to gain insights into the ALD process of Al2O3from trimethylaluminum and water on hydrogenated and oxidized Ge(100) surfaces. We deciphered the origin for the different peculiarities during initial ALD cycles for the deposition on both surfaces. While the simulations predicted a nucleation delay for hydrogenated Ge(100), a self-cleaning effect was discovered on oxidized Ge(100) surfaces and resulted in an intermixed Al2O3/GeOxlayer that effectively suppressed oxygen diffusion into Ge. In situ spectroscopic ellipsometry in combination with ex situ atomic force microscopy and X-ray photoelectron spectroscopy confirmed these simulation results. Electrical impedance characterizations evidenced the critical role of the intermixed Al2O3/GeOxlayer to achieve electrically well-behaved dielectric/Ge interfaces with low interface trap density. The combined approach can be generalized to comprehend the deposition and reaction kinetics of other ALD precursors and surface chemistry, which offers a path toward a theory-aided rational design of ALD processes at a molecular level.
authors.forename: Yuanxia
authors.identifier: http://orcid.org/0000-0003-1314-7717
authors.initials: Y
authors.lastname: Zheng
authors.forename: Sungwook
authors.initials: S
authors.lastname: Hong
authors.forename: George
authors.initials: G
authors.lastname: Psofogiannakis
authors.affiliation: Kurt J. Lesker Company , Pittsburgh, Pennsylvania 15025, United States.
authors.forename: G Bruce
authors.initials: GB
authors.lastname: Rayner
authors.affiliation: Department of Electrical Engineering, University of Notre Dame , Notre Dame, Indiana 46556, United States.
authors.forename: Suman
authors.initials: S
authors.lastname: Datta
authors.forename: Adri C T
authors.initials: ACT
authors.lastname: van Duin
authors.forename: Roman
authors.initials: R
authors.lastname: Engel-Herbert
keywords: ALD; ReaxFF; germanium; nucleation; self-cleaning; spectroscopic ellipsometry