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An original integrated approach developed within a multiscale strategy, which combines first-principles quantum simulations and kinetic Monte Carlo (KMC), is presented to investigate the atomic layer deposition (ALD) of HfO2 on Si(100) surface. Density functional theory within the hybrid functional is used to determine the detailed physicochemical mechanisms and associated energetics of the two half cycles taking place during the initial stage of film growth. A kinetic Monte Carlo model is then proposed that deals with the stochastic nature of the calculated DFT mechanisms and barriers. Beyond the chemical information emanating from DFT calculations, the lattice-based KMC approach requires preliminary physical considerations issued from the crystal structures that the system is intended to adopt. This is especially critical in the case of heterogeneous systems like oxides deposited on silicon. We also describe (i) how atomistic configuration changes are performed as a result of local events consisting in elementary reaction mechanisms occurring on specific lattice sites, (ii) the temporal dynamics, governed by transition probabilities, calculated for every event from DFT activation barriers, and (iii) the relation of KMC with the ALD experimental procedure. Some preliminary validation results of the whole multiscale strategy are given for illustration and pertinence with regard of the technological main issues.

Using density functional theory calculations, we address the structural phase transition from the covalent metallic precursor molecules to their oxide layer structure during the gas-phase deposition process. We observe that the associated increase in the metal coordination number during the gas–solid transition, i.e., the redistribution mechanisms of oxygen atoms around the metal atoms, are identical and barrierless for Sn- or Hf-based precursors. These mechanisms, occurring in the grown oxide layers, are shown to be present at the early stage of gas phase agglomeration reactions, giving rise to unexpected species. The presence of OH hydroxyl groups on the surface/hydroxylated precursors are mainly responsible for this transition. Finally, we discuss the relevance of our calculations within the framework of the metal oxides growth by ALD process.

A three-dimensional kinetic Monte Carlo (KMC) model has been developed and used to simulate the microstructure and growth morphology of cubic transition metal nitride (TMN) thin films deposited by reactive magnetron sputtering. Results are presented for the case of stoichiometric TiN, chosen as a representative TMN prototype. The model is based on a NaCl-type rigid lattice and includes deposition and diffusion events for both N and Ti species. It is capable of reproducing voids and overhangs, as well as surface faceting. Simulations were carried out assuming a uniform flux of incoming particles approaching the surface at normal incidence. The ballistic deposition model is parametrized with an interaction parameter r 0 that mimics the capture distance at which incoming particles may stick on the surface, equivalently to a surface trapping mechanism. Two diffusion models are implemented, based on the different ways to compute the site-dependent activation energy for hopping atoms. The influence of temperature (300-500 K), deposition flux (0.1-100 monolayers/s), and interaction parameter r 0 (1.5-6.0Å) on the obtained growth morphology are presented. Microstructures ranging from highly porous, [001]-oriented straight columns with smooth top surface to rough columns emerging with different crystallographic facets are reproduced, depending on kinetic restrictions, deposited energy (seemingly captured by r 0 ), and shadowing effect. The development of facets is a direct consequence of the diffusion model which includes an intrinsic (minimum energy-based) diffusion anisotropy, although no crystallographic diffusion anisotropy was explicitly taken into account at this stage. The time-dependent morphological evolution is analyzed quantitatively to extract the growth exponent β and roughness exponent α, as indicators of kinetic roughening behavior. For dense TiN films, values of α ≈ 0.7 and β = 0.24 are obtained in good agreement with existing experimental data. At this stage a single lattice is considered but the KMC model will be extended further to address more complex mechanisms, such as anisotropic surface diffusion and grain boundary migration at the origin of the competitive columnar growth observed in polycrystalline TiN-based films.

In this work, TiN, ZrN and HfN thin films fabricated using glancing angle deposition (GLAD) technique are studied both experimentally and by numerical simulations. The films (1 µm thickness) were deposited by reactive magnetron sputtering at 0.3 Pa and 300°C on Si substrates inclined at α=85° with respect to the target. The film morphology and crystal structure were characterized by scanning electron microscopy, atomic force microscopy and Xray diffraction (XRD), including pole figure measurements. The wettability of these coatings was investigated using the sessile drop method with three different liquids. It is shown that TiN, ZrN and HfN films have a cubic, NaCl-type crystal structure with a [111] out-of-plane orientation and exhibit a biaxial texture. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids. The films develop columnar microstructures, with typical column widths of ~ 100 nm. The tilt angle β of the columns is found to increase from 24.5, 31.5 to 34° for TiN, ZrN and HfN films, respectively. Atomistic computations of the growth of these nitrides at glancing angle using a kinetic Monte Carlo model reveal that the growth morphology and variation in column tilt angle is well reproduced by considering the difference in the angular distribution of the sputtered particles.This study also shows that GLAD films are hydrophilic comparatively to the same films deposited at near-normal incidence, and among the three nitrides, TiN is the more wettable coating.

In this study, polycrystalline hafnium nitride (HfN) thin films were grown by oblique angle deposition (OAD) technique to investigate the relationship between column tilt angle, texture development and residual stress evolution with varying inclination angle α of the substrate. The films (~1 μm thickness) were grown at various angles (α = 5°, 25°, 35°, 65°, 75°, and 85°) with respect to the substrate normal by reactive magnetron sputtering at 0.3 Pa and 300 °C. The film morphology, crystal structure and residual stress state were characterized by scanning electron microscopy and X-ray diffraction (XRD), including pole figure and sin2ψ measurements. All HfN films had a cubic, NaCl-type crystal structure with an [111] out-of-plane orientation and exhibited a biaxial texture for α ≥ 35°. XRD pole figures reveal that the crystal habit of the grains consists of {100} facets constituting triangular-base pyramids, with a side and a corner facing the projection of the incoming particle flux (indicative of a double in-plane alignment). A columnar microstructure was formed for α ≥ 35°, with typical column widths of 100 nm. It is observed that the column tilt angle β increases monotonously for α ≥ 35°, reaching β = 34° at α = 85°. This variation at microscopic scale is correlated with the tilt angle of the (111) crystallographic planes, changing from −24.8 to 11.3° with respect to the substrate surface. The residual stress changes from strongly compressive (~−5 GPa at α = 5°) to negligible or slightly tensile for α ≥ 35°. The observed trends are compared to previous works of the literature and discussed based on existing crystal growth and stress models, as well as in light of energy and angular distribution of the incident particle flux calculated by Monte Carlo. Importantly, a decrease of the average kinetic energy of Hf particles from 22.4 to 17.7 eV is found with increasing α due to an increase number of collisions.

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Density Functional Theory calculations are used to map out the preferential oxygen molecule adsorption sites and oxygen atom incorporation on germanium (100) surface. A comparison with primary oxidation mechanisms encountered in pure silicon and silicon germanium (100) surfaces is presented here. This study highlights opposite substrates behaviors facing oxygen molecule adsorption: 1/ surface germanium atoms move from their crystalline positions to adapt to the approaching oxygen molecule resulting in adsorbed peroxide bridge configuration, whereas oxygen molecule is fully dissociated in strand configuration on a silicon surface 2/ oxygen atoms tend to avoid each other on germanium surface whereas oxide nucleus can be observed on silicon surface even at the early steps of the oxidation process. Results show that germanium surface appears to be less reactive than the silicon substrate towards molecular oxygen species.