Couches minces d'oxynitrure de tantale déposées par pulvérisation réactive. Étude du système Ta-Ar-O2-N2 et caractérisation des films

Le but de ce travail de thèse est d étudier les propriétés d un plasma réactif ainsi que les caractéristiques structurales, optiques et électriques de couches minces d oxynitrure de tantale (TaOxNy) élaborées par pulvérisation cathodique radiofréquence. L élaboration de ce matériau ternaire par pulvérisation d une cible de tantale au moyen d un plasma contenant à la fois de l argon, de l oxygène et de l azote est complexe en raison de phénomènes d empoisonnement de la cible. L analyse de la composition du plasma par spectroscopie d émission optique et le suivi de l évolution de certaines raies représentatives d espèces excitées dans le milieu, nous ont permis de déterminer les conditions optimales au dépôt de films de types TaOxNy sur une large gamme de compositions. Grâce à une étude par diffraction des rayons X et spectroscopie de photoélectrons X, nous avons suivi les évolutions structurales de couches ayant subi ou non un recuit thermique. Nous avons montré de quoi étaient constituées les parties amorphes et cristallisées de ces films et déterminé la taille des domaines de cohérence. Enfin, les propriétés optiques (indice de réfraction, gap optique, paramètre d Urbach) et diélectriques ont été corrélées à la structure des matériaux.The aim of this thesis is to study the properties of a reactive plasma as well as the structural, optical and electrical properties of tantalum oxynitride thin films (TaOxNy) prepared by radiofrequency sputtering. The elaboration of this ternary material by sputtering a pure tantalum target using plasma containing both of argon, oxygen and nitrogen is complex due to the target-poisoning phenomenon. The analysis of the composition of the plasma by optical emission spectroscopy and monitoring the evolution of some representative line of excited species in this environment, allow us to determine the optimal conditions to deposit TaOxNy films over a wide range of composition. Thanks to a study by X-ray diffraction and X-ray photoelectron spectroscopy, we followed the structural evolution of the films subjected or not to a rapid thermal annealing. We showed by what were constituted the amorphous and crystalline parts of the films and determined the size of the crystalline domains. Finally, the optical properties (refractive index, optical gap, Urbach parameter) and dielectric behavior have been correlated with the structure of materials.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Dépôt de couches minces par plasma pulsé radiofréquence et basse pression en mélange hexaméthyldisiloxane / oxygène

L'objectif de cette thèse est d'étudier le dépôt chimique en phase vapeur assisté par plasma (PECVD), à basse pression (3mTorr) et basse température (< 100C), en plasma pulsé (10Hz-1kHz) d'hexaméthyldisiloxane (HMDSO)/ oxygène dans un réacteur hélicon radiofréquence. La cinétique des espèces chargées et de certaines espèces neutres actives est déterminée à partir de mesures résolues en temps par sonde de Langmuir et spectroscopie d'émission optique. La caractérisation des dépôts par ellipsométrie, absorption infraouge et gravimétrie montre que des films inorganiques (SiO2) ou organiques (SiOxCyHz) peuvent être obtenus avec un même mélange de gaz suivant les paramètres de pulse. La structure et la vitesse de dépôt sont liées au temps de création et de perte des atomes d'oxygène. La réduction du bombardement ionique lors du dépôt en plasma pulsé permet de réduire les contraintes en compression et d'améliorer les propriétés électriques des films de SiO2.This work concerns the Plasma Enhanced Chemical Vapour Deposition (PECVD) of thin films, at low pressure (3mTorr) and low temperature (<100C), in Hexamethyldisiloxane (HMDSO)/ oxygen pulsed plasmas in a radiofrequency helicon reactor. The kinetics of charged species and of some neutral active species is investigated by Langmuir probe and optical emission spectroscopy time-resolved measurements. The film analysis by ellipsometry, infrared spectroscopy and gravimetry shows inorganic SiO2-like and plasma polymers SiOxCyHz films can be deposited with a fixed gas mixture depending on the pulse parameters. The structure and deposition rate are linked to the creation and loss times of oxygen atoms. The reduction of ion bombardment in pulsed plasma also allows to reduce the compressive stress and to improve the electrical properties of SiO2-like films, as demonstrated by nano-indentation, Newton's ring method, and C(V) and I(V) measurements on MOS structure.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Multiphase Structure of Tantalum Oxynitride TaOxNy Thin Films Deposited by Reactive Magnetron Sputtering

International audienceThis work deals with the structure and the microstructure of tantalum oxynitride thin films deposited by reactive magnetron sputtering. The local structures of amorphous as-prepared thin films are investigated using the pair distribution function (PDF) technique based on total X-ray scattering experiments. The corresponding annealed thin films are analyzed using conventional θ–θ X-ray diffraction technique and full-pattern fitting methods. Rutherford backscattering and X-ray photoelectron spectrometries are used in conjunction with X-ray techniques. As-prepared thin films are nanostructured. The PDF signal is coming from small structural units below 10 Å in diameter, which only maintain nearest-neighbor order and with a composition changing gradually from TaN to δ-TaON and Ta2O5 as the oxygen content in the reactive gas increases. On the other hand, the annealed thin films consist of a mixture of separate crystalline phases with refined cell parameters consistent with the formation of TaN (Fm–3m), β-TaON (P21/c), and Ta2O5 (C2mm) more or less successively as the oxygen content in the reactive gas increases. Information on the size of the coherent domains and the preferential growth orientation are obtained from analysis of anisotropic diffraction line broadening effects in the XRD patterns. The results are in favor of a random bonding model (RBM) in the case of as prepared thin film and random mixture model (RMM) for annealed samples

In Situ Monitoring of Cu(In1-x,Gax)Se2 Composition and Target Poisoning by Real Time Optical Emission Spectroscopy During Deposition From a Hybrid Sputtering/Evaporation Process.

International audienceCu(In1−x,Gax)Se2 (CIGS) thin films can be deposited with a high versatility of composition by a hybrid one-step co-sputtering/evaporation process. In this paper, plasma analysis is performed with an optical emission spectroscopy non-contact tool, following light emissions from different plasma species: sputtered copper, gallium, indium but also evaporated selenium. The variations of plasma characteristics are correlated with target self-bias voltage. Hence, the selenium flow threshold avoiding target poisoning and the main parameter controlling the CIGS composition are determined. This study allows us to set up a process calibration method by means of correlation between the selenium evaporation temperature and the elemental composition of the deposited thin film

Broadband and Wide-Temperature-Range Thermal Emitter with Super-Hydrophobicity Based on Oxidized High-Entropy Film

International audienceThis paper demonstrates a broadband and wide-temperature-range thermal emitter with super-hydrophobicity based on an oxidized high-entropy film. The annealed (NiCuCrFeSi)O high-entropy film can serve as a mid-infrared emitter due to its three characteristics: (i) high blackbody-like emission in a broadband mid-infrared region from 2.5 to 20 μm; (ii) high emittance (more than 90%) in a wide temperature range from 300 to 1000 K; (iii) super-hydrophobicity with a high contact angle of 151° and low tilt angle of 5°. These characteristics originate from the recrystallization of the as-deposited film and formation of a cavernous structure with a plethora of nanoscale polyhedrons and holes after an annealing process, supported by the results of XRD and SEM/EDX. This work may provide new ideas for applications of thermal emitters operating at a substantially wide temperature range

Control the Composition of Tantalum Oxynitride Films by Sputtering a Tantalum Target in Ar/O2/N2 Radiofrequency Magnetron Plasmas.

International audienceTantalum oxynitride films can be deposited with a high versatility in composition by reactive sputtering of a tantalum target in Ar/O2/N2 mixtures. In this paper, plasma analysis was performed from simple to more complex Ar/O2/N2 gas mixtures and linked to the layer elemental composition. The presence of two reactive gases accelerates the appearance of Compound Sputtering Mode and modifies the nature of target surface. Hence, in Ar/O2/N2, nitrogen addition can lead to poison the target surface by a nitride but also by an oxide or by an oxynitride. Finally, this comprehension of interaction between target and reactive gas was used to select suitable flow rate conditions allowing tantalum oxynitride deposition with varying optical propertie

In-situ optical emission spectroscopy for a better control of hybrid sputtering/evaporation process for the deposition of Cu(In,Ga)Se2 layers.

International audienceIn this work, we have developed a hybrid one-step co-sputtering/evaporation Cu(In,Ga)Se2 (CIGS) process, where Cu, In and Ga are sputtered simultaneously with the thermal evaporation of selenium, thus avoiding the H2Se use. An appropriate control of the selenium flux is very important to prevent the target poisoning and hence some material flux variations. Indeed, the control of the CIGS composition must be rigorous to ensure reproducible solar cell properties. In this regard, a study of the correlations between plasma species and thin film composition, structure and morphology has been performed by varying power values and Se evaporation temperature in the 170 to 230 °C range. We started by studying the plasma with a powerful technique: optical emission spectroscopy, following light emissions from different plasma species: sputtered Cu, Ga, In but also evaporated Se. Hence, we determined the Se flow threshold avoiding target poisoning and the main parameter controlling the CIGS composition. Obviously, we also focused our interest on the material. We measured film composition and thickness of the samples with X-ray fluorescence and by energy dispersive X-ray. Different phases formed during the process were identified by Raman spectroscopy and X-ray diffraction. The optoelectronic cell properties showed promising efficiency of 10.3% for an absorber with composition ratios of [Cu]/([In] + [Ga]) = 1.02 and [Ga]/([In] + [Ga]) = 0.44. Finally, this work shows that we are able to control this hybrid process and thus the structure and composition of CIGS thin film for industrial transfer in the photovoltaic field

Electrochromic Thin Films Based on NiAl Layered Double Hydroxide Nanoclusters for Smart Windows and Low-Power Displays

International audienceTo develop electrochromic thin films for smart windows and low-power displays, homogeneous thin films were produced by spin coating colloidal NiAl layered double hydroxide (LDH) nanocluster solutions on a fluorine-doped tin oxide (FTO) glass substrate. The nano-LDH dispersion was synthesized via a facile one-step epoxide mediated process at room temperature. In situ relative transmittance measurements at 400 nm, recorded during potential scans in cyclic voltammetry or differential pulse chronoamperometry, showed the electrochromic behavior of the homogeneous thin films. The impact of various parameters on the electrochromic properties of the films was detailed, such as the thickness of the film, the nature of the electrolyte, and the presence of electroactive anions. The electrochromic properties, namely, the change in transmittance (ΔT) and the bleaching reversibility, were greatly improved using alkaline metal hydroxide as the electrolyte and in the presence of Fe(CN)64–. The performances that we reached from the deposition of nanoclusters can be advantageously compared to the literature with ΔT = 70% and fast and good reversibility. Upon calcination, the NiAl-LDH film converted into mixed oxides (NiO and NiAl2O4). The higher the calcination temperature, the lower was the ΔT value. The presence of porosity within the thin films, through the introduction of sacrificial polymeric beads and then decomposition at 400 °C, was investigated, highlighting an enhancement of the ΔT value attributed to better accessibility to the nickel redox sites

Tailoring the structural and optical properties of bismuth oxide films deposited by reactive magnetron sputtering for photocatalytic application

International audienceBismuth oxide thin films were deposited by room temperature reactive magnetron sputtering of a bismuth target in different Ar/O2 atmospheres. The analysis of their structures and compositions shows that the films are formed of different phases depending on the oxygen flow rate (ՓO2). Films deposited at low ՓO2 consist of mixtures of crystalline metallic bismuth (Bio) and bismuth oxide phase (Bi2O3). Moreover, XPS analysis revealed the contribution of different oxidation states of bismuth related to Bio and Bi3+ in Bi2O3. The optical properties were investigated by spectroscopic ellipsometry and confirmed by UV–Vis spectroscopy. As ՓO2 increases above 1 sccm, bismuth oxide films become more transparent. They highly transmit light in the visible range, and the optical absorption edge shifts to short-wavelength such that the films exhibit higher bandgap values. Furthermore, the photocatalytic performance was determined upon comparing the degradation of 6.6 × 10−5 M of methyl orange (MO) under UV–Vis irradiation in the presence of different thin films. Results show that the low crystallinity, the improved optical absorption, as well as the existence of Bio in small proportion, increase the separation efficiency of the generated e−/h+ pairs inhibiting their recombination, thus enhancing the photocatalytic degradation of MO dye

Structural and ellipsometric study on tailored optical properties of tantalum oxynitride films deposited by reactive sputtering

International audienceOxynitride materials, which offer the possibility of merging oxide and nitride properties, are increasingly studied for this reason. This paper focuses on assessing the optical properties of tantalum oxynitride thin films deposited by pure tantalum target sputtering in an Ar/O2/N2 reactive atmosphere. First, by changing the oxygen to reactive gas flow rate ratio, and using thermal post-treatment, we deposited films with elemental compositions studied by Rutherford backscattering spectroscopy, ranging from a nitride (close to Ta3N5) to an oxide (close to Ta2O5) with various structures analyzed by x-ray diffraction. Their optical properties were investigated in depth by spectroscopic ellipsometry and UV-visible spectroscopy. For the ellipsometry investigation, we propose a model combining the Tauc–Lorentz law and additional Lorentz oscillator: the first contribution is linked to a semi-conductor or insulator film matrix, and the second one to the presence of conductive TaN crystals. Ellipsometry thus appears as a powerful tool to investigate complex materials such as tantalum oxynitrides. Moreover, we demonstrated that using this deposition method we were able to finely tune the film refractive index from 3.4 to 2.0 (at 1.96 eV) and the optical band gap, specifically from 1.3 to 2.7 eV