Nanocolumnar TiN thin film growth by oblique angle sputter-deposition: Experiments vs. simulations

Nanostructured columnar titanium nitride (TiN) thin films were produced by oblique angle deposition using reactive magnetron sputtering. The influence of the angular distribution of the incoming particle flux on the resulting filmmorphology (columntilt angle, porosity, surface roughness) was studied by varying the inclination angle α of the substrate at two different working pressures, 0.3 and 0.5 Pa. The microstructural features and columns tilt angles βexp determined experimentally were compared to those simulated from two kinetic Monte Carlo (KMC) models. With increasing pressure, the TiN columns were found to be less defined but no significant changes in βexp were revealed. Both KMC models satisfactorily reproduced the experimental findings, the agreement being closer at 0.5 Pa. The evolution of β angle is also discussed with respect to the resulting incidence angle θres of the incoming flux, this latter quantity accounting for the local incidence angle of individual particles,which may greatly differ fromthe geometrical angle α, especially at highworking pressure due to the incoming particle – gas collisions. Crossover phenomena between the 0.3 and 0.5 Pa series were revealed from the evolution of the film resistivity, as well as simulated layer density and surface roughness versus α angle.This work has been performed within the M.ERA-NET project MC2 “Multi-scale Computational-driven design of novel hard nanostructured Coatings” and funded by the French ANR program (Project No. ANR-13-MERA-0002-02). BB acknowledges the financial support from the Algerian Ministry of Higher Education and Scientific Research through the grant n°173 of the PNE 2016-17 program

On the effect of copper as wetting agent during growth of thin silver films on silicon dioxide substrates

We study the effect of Cu incorporation on the morphological evolution and the optoelectronic properties of thin Ag films deposited by magnetron sputtering on weakly-interacting SiO2 substrates. In situ and real time spectroscopic ellipsometry data show that by adding up to 4at.% Cu throughout the entire film deposition process, wetting of the substrate by the metal layer is promoted, as evidenced by a decrease of the thickness at which the film becomes continuous from 19.5nm (pure Ag) to 15nm (Ag96Cu4). The in situ data are consistent with ex situ x-ray reflectometry analyses which show that Cu-containing films exhibit a root mean square roughness of 1.3nm compared to the value 1.8nm for pure Ag films, i.e., Cu leads to smoother film surfaces. These morphological changes are coupled with an increase in continuous-layer electrical resistivity from 1.0×10-5Ωcm (Ag) to 1.25×10-5Ωcm (Ag96Cu4). Scanning electron microscopic studies of discontinuous layers reveal that the presence of Cu at the film growth front promotes smooth surfaces (as compared to pure Ag films) by hindering the rate of island coalescence. To further understand the effect of Cu on film growth and electrical properties, in a second set of experiments, we deploy Cu with high temporal precision to target specific film-formation stages. The results show that longer presence of Cu in the vapor flux and the film growth front promote flat morphology. However, both a flat surface and a continuous-layer electrical resistivity that is equal to that of pure Ag films can only be achieved when Cu is deployed during the first 2.4nm of film deposition, during which morphological evolution is, primarily, governed by island coalescence. Our overall results highlight potential pathways for fabricating high-quality multifunctional metal contacts in a wide range of optoelectronic devices based on weakly-interacting oxides and van der Waals materials.Funding agencies: The French Government program "Investissements d’Aveni"r (LABEX INTERACTIFS, reference ANR-11-LABX-0017-01), Linköping University ("LiU Career Contract, Dnr-LiU-2015-01510, 2015-2020"), The Swedish research council (contract VR-2015-04630), The ÅForsk foundation (contracts ÅF 19-137 and ÅF 19-746), The Olle Engkvist foundation (contract SOEB 190-312), The Wenner-Gren foundations (contracts UPD2018-0071 and UPD2019-0007)</p

Croissance, structure et propriétés électroniques des nitrures ternaires de métaux de transition en films minces

Les échantillons de nitrures ternaires de métaux de transition ont été élaborés par trois techniques de dépôt différentes : Pulsed Laser Deposition (PLD), pulvérisation magnétron (PUMA) et pulvérisation sous faisceau d'ions (DIBS). Les propriétés structurales et optiques des échantillons ont été caractérisées par diffraction des rayons X (XRD) et par spectroscopie de réflectivité optique (SRO). Des mesures de composition ont également été effectuées par spectroscopie d'électrons Auger (AES) et par spectroscopie de rayons X à dispersion d'énergie (EDXS). Les contraintes ont été déterminées en mesurant la courbure du substrat et en utilisant des techniques de diffraction des rayons X. Les analyses microstructurales ont révélé que tous les échantillons ont cristallisé dans la structure NaCl et le paramètre de réseau suit la loi de Vegard. Les propriétés optiques de ces films sont assimilables à celles des conducteurs. Les mesures de contraintes ont révélé que les films sont en compression.Ternary nitride samples of transition metals were grown by three different deposition techniques; Pulsed Laser Deposition (PLD), Magnetron Sputtering (MS) and Dual Ion Beam Sputtering (DIBS). These samples were characterized structurally and optically by X-ray diffraction (XRD) and Optical Reflectance Spectroscopy (ORS) respectively. Compositional measurements have also been performed by Auger Electron Spectroscopy (AES) and Energy Dispersive X-rays (EDX). Stress measurements were performed using wafer curvature and X-ray diffraction techniques. Structure analysis has reveals that all grown samples were stabilized in the rocksalt structure and the lattice constant size follows the vegard s rule. The optical properties of the films were similar to conductors, excibiting strong Drude behavior. Stress measurements analysis revealed that the films are under compressive stress and the stress state is depending on energetic conditions.POITIERS-BU Sciences (861942102) / SudocSudocFranceGreeceFRG

Tuning high power impulse magnetron sputtering discharge and substrate bias conditions to reduce the intrinsic stress of TiN thin films

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Contraintes, microstructure et sollicitation sous irradiation aux ions de films minces élaborés par pulvérisation ionique (modélisation et application à l'étude des effets interfaciaux dans des multicouches métalliques)

Le mélange interfacial dans les multicouches Mo/Ni a été étudié. Pour cela, des multicouches épitaxiées Mo(110)/Ni(111) ont été élaborées par évaporation thermique et pulvérisation ionique. Au préalable, nous avons développé un modèle de contrainte qui permet de rendre compte des déformations volumiques observées dans les films élaborés par pulvérisation ionique et qui surtout donne accès au paramètre de maille non contraint et libre de défauts a0 uniquement lié aux effets chimiques. L'irradiation aux ions a été utilisée pour contrôler le niveau de contrainte, déterminé essentiellement par diffraction des rayons X. Il a alors été possible de déterminer la valeur de a0 dans les sous-couches de Mo des multicouches Mo/Ni. Une tendance à la ségrégation' de Ni dans Mo est observée, indépendamment des conditions de dépôt, ce qui suggère que des forces thermodynamiques sont favorables au mécanisme d'échange, phénomène dont l'amplitude est clairement accentuée par les effets balistiques.We investigated the interfacial mixing in Mo/Ni multilayers. For this purpose, Mo(110)/Ni(111) multilayers were grown by thermal evaporation and direct ion beam sputtering. As a preliminary, we developed a stress model that accounts for volume strains observed in sputtered thin films and above all allows to determine the unstressed and free of defects lattice parameter a0 solely linked to chemical effects. Ion irradiation was used to control the stress level, which was essentially determine by X-ray diffraction. Thus, the stress analysis enabled us to determine the a0 values in Mo sub-layers of Mo/Ni superlattices. A tendency to the formation of an interfacial alloy is observed independently of the growth conditions, which suggests that thermodynamic forces favour the exchange mechanism. However, the extent of the intermixing effect is clearly enhanced by ballistic effects.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Influence of particle and energy flux on stress and texture development in magnetron sputtered TiN films

The real-time stress evolution during reactive dc magnetron sputter deposition of TiN films in Ar+N-2 plasma discharge was measured in situ using a multiple-beam optical stress sensor, while the film texture was determined ex situ using x-ray diffraction. The influence of atomic N/Ti flux and energy flux, previously quantified by combining plasma characterization and Monte Carlo simulations (2009 J. Phys. D: Appl. Phys. 42 053002), was investigated by varying either the N-2 partial pressure at fixed total pressure, the total working pressure or the bias voltage applied to the substrate. The contribution of thermal stress was carefully taken into account from thermal probe measurements to evaluate the intrinsic (growth) stress from the measured film force data. A clear correlation between stress, film texture and energy flux is evidenced: while underdense (1 1 1)-textured TiN films with 'V'-shaped columnar growth (zone T) are under tensile stress (up to +0.6 GPa), dense TiN films with zone II microstructure develop a (0 0 2) texture and large compressive stress (up to 3GPa) when the energy flux is higher than similar to 150 eV per incoming particle. However, it is shown that a positive or negative bias voltage, though increasing the energy flux, did not promote a (0 0 2) texture. It is concluded that compressive stress development and (0 0 2) preferential growth are both kinetically driven processes in magnetron sputtered TiN layers, but exhibit distinct dependence with the substrate fluxes

Interdépendance entre contraintes, transition de phase et nanostructure lors de la croissance par pulvérisation magnétron de films métalliques (application au système Mo-Si)

Ce travail porte sur la compréhension des mécanismes de génération de la contrainte durant la croissance 2D de films métalliques de basse mobilité. L'évolution de la contrainte est suivie in-situ et en temps réel durant la croissance par pulvérisation magnétron de films Mo-Si par mesure de la courbure du substrat. Le dispositif optique multi-faisceaux utilisé offre une sensibilité sub-monocouche et permet ainsi de détecter des changements subtils de la contrainte de surface/interface, les transitions structurales et la formation de défauts dans le film. Les réusltats sont interprétés et discutés sur la base d'obesrvations ex-situ XRD, ESBD, HRTEM et AFM. Il est montré la possibilité d'ajuster la contrainte en changeant les conditions de nucléation, le flux et l'énergie des particules incidentes. Pour les solutions solides métastables Mo1 xSix sur a-Si, l'établissement au-delà d'une épaisseur critique d'une contrainte de tension, corrélée à l'augmentation de la taille latérale des grains, est attribuée à un changement de volume à la cristallisation du film. En revanche, pour des conditions similaires de dépôt, un état stationnaire en compression se développe dans les films dont la croissance est initiée sur c-Mo, après un stade initial en tension résultant d'une croissance en épitaxie, la formation de défauts est identifiée comme la source principale de cette contrainte compressive. Selon l'énergie des espèces pulvérisées, les atomes s'incorporent préférentiellement dans les joints de grains ou en interstitiel dans le grain, ce qui conduit à deux états distincts de contrainte, comme le révèlent les analyses XRD ex-situ.This work is focused on understanding the underlying mechanisms for stress generation and relaxation during the 2D growth of low mobility metal thin films, an issue which remains largely unexplored. Stress evolution was monitored in situ and in real time during growth of Mo-Si magnetron-sputtered films on various substrates using the substrate curvature technique. A multi-beam optical stress sensor was used, wich offers a sub-monolayer sensitivity and enables to probe changes in surface/interface stress, structural transitions and defect incorporation. The results are interpreted and discussed based on microstructural analysis using ex-situ XRD, EBSD, HRTEM and AFM observations. It is shown that the stress can be tailored by changing the nucleation conditions, the flux and energy of incoming particles. For Mo1 xSix metastable solid solutions on a-Si, a tensile stress rise, wich develops after the film has become crystalline, is correlated with an increase in lateral grain size, and attributed to the volume change at the crystallization. By contrast, for the same deposition conditions, a compressive steady-state develops in films grown on c-Mo, after an initial tensile stress due to epitaxial coherence strain. Incorporation of excess atoms in the growing layer is identified as the main compressive stress source. We show that this process is driven by ballistic energy transfer. Depending on the deposited energy, atoms incorporates preferably at the grain boundary or in the bulk of grain, resulting in distinct stress states as revealed by XRD on ion irradiated films. Interdependence betwenn the structural, electrical and elastic properties of Mo1 xSix films is revealed.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Computational approach to identify structural and elastic relationship in metastable crystalline and amorphous alloy thin films: Mo1-xNix and Mo1-xSix case studies

International audiencePreviously well-established experimental trends of ground-state properties of crystalline and amorphous Mo1-xSix and Mo1-xNix alloys with 0 ≤ x ≤ 1 are predicted by first-principles calculations and inter-relationship with sound velocities and elastic properties are identified. The free energy of mixing, calculated at 300 K provides accurate values of the critical Si and Ni concentrations leading to the crystalline-to-amorphous transition. Specifically, a transition from BCC to amorphous state is predicted for xSi ~ 0.14 and xNi ~ 0.32, while FCC to amorphous transition is observed for xNi ~ 0.77. These structural transitions are accompanied by modifications of the out-of-plane longitudinal and shear elastic constants. In the crystalline region, a pronounced softening of elastic moduli is predicted for both solid solution alloys. While for amorphous Mo-Ni, the elastic constants do not undergo significant changes, for amorphous Mo-Si, they exhibit two distinct behaviors depending on the electronic properties and bonding character. For 0.2 ≤ xSi ≤ 0.7, the metallic character of the amorphous alloys is maintained and the elastic properties are remarkably stable. For xSi > 0.7, a progressive increase in the atomic volume is observed and the amorphous alloys acquire a covalent character and a reduced coordination number. Surprisingly, during this transition, both the longitudinal and shear acoustic velocities continuously increase, despite a progressive softening of the elastic stiffness constants. These calculations provide deep insight at the atomic-scale and reproduce satisfactorily the earlier experimental works of magnetron co-sputtered Mo-Si films, while some disagreement on elastic properties remain for more energetic ion beam sputtered Mo-Ni films, likely partially attributed to point-defects

Texture and Stress Evolution in HfN Films Sputter-Deposited at Oblique Angles

International audienceIn 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