Miniaturiser les composants impose des changements radicaux pour l'élaboration des dispositifs micro électroniques du futur. Dans ce cadre, les oxydes de grille MOS atteignent des épaisseurs limites qui les rendent perméables aux courants de fuite. Une solution est de remplacer le SiO2 par un matériau de permittivité plus élevée permettant l'utilisation de couches plus épaisses pour des performances comparables. Dans ce travail nous présentons une modélisation multi-échelle de la croissance par couche atomique (ALD) d'HfO2 sur Si permettant de relier la nano-structuration d'une interface au procédé d'élaboration. Nous montrons que la connaissance de processus chimiques élémentaires, via des calculs DFT, permet d'envisager une simulation procédé qui repose sur le développement d'un logiciel de type Monte Carlo Cinétique nommé "HIKAD". Au delà des mécanismes les plus évidents, adsorption, désorption, décomposition et hydrolyse des précurseurs sur la surface, nous introduirons la notion de mécanismes de densification des couches d'oxyde déposées. Ces mécanismes sont l'élément clé permettant de comprendre comment s'effectue la croissance de la couche en termes de couverture. Mais au delà de cet aspect ils nous permettent d'appréhender comment, à partir de réactions de type moléculaire le système évolue vers un matériau massif. Nous discuterons ces divers éléments à la lumière de résultats de caractérisations obtenus récemment sur le plan expérimental du dépôt d'oxydes d'hafnium.

A partir du noeud technologique 45 nm, le remplacement de l'oxyde de grille SiO2 par un diélectrique high-κ est nécessaire pour poursuivre la loi de Moore : l'introduction d'un tel matériau permet de maintenir une capacité de grille élevée tout en limitant le courant de fuite parasite à travers la couche diélectrique. Toutefois, les mécanismes physiques à l'origine de la réduction de courant restent méconnus. Ce manuscrit présente une étude complète de la conduction électrique dans un empilement oxyde d'interface - high-κ - grille métallique. Nous présentons dans un premier temps la modélisation Poisson-Schrödinger développée pour rendre compte de l'effet de confinement à l'interface du Silicium, prenant en compte la pénétration de charge dans l'empilement et traitant de la non-parabolicité de la bande de valence. Une étude expérimentale étendue met ensuite en évidence les mécanismes physiques à l'origine de la conduction, en s'appuyant sur un ensemble de caractéristiques Ig(Vg) et C(Vg) d'empilements d'épaisseurs variables, mesurées à basse et haute température. Des approches originales pour modéliser le transport permettent également d'établir les paramètres tunnel et la structure de bande du HfO2, tout en soulignant la nature sous-stoechiométrique de l'oxyde d'interface. Enfin, ces résultats sont appliqués à l'étude de la conduction dans des empilements high-κ avec additifs Lanthane et Magnésium, et mettent en évidence la formation d'un dipôle contribuant à diminuer la tension de seuil.

My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO2 films were deposited on Al2O3 substrates by pulsed-laser deposition. Xray- diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films.

La miniaturisation des dispositifs CMOS impose d'introduire de nouveaux matériaux dans l'empilement de grille des transistors. Ainsi, l'empilement classique poly-silicium/SiO2 est remplacé par un empilement poly- silicium/métal/matériau à haute permittivité diélectrique. L'introduction de ces nouveaux matériaux nécessite le développement de nouveaux procédés de gravure plasma.<br />L'objectif de ce travail est de proposer un procédé de gravure plasma capable de graver une fine couche de diélectrique (HfO2 dans notre cas) sélectivement par rapport au substrat de silicium sous-jacent. Cette étude montre que les plasmas à base de BCl3 sont très prometteurs dans ce domaine. En effet, les mécanismes de gravure en BCl3 reposent sur une compétition entre gravure et formation d'un dépôt de BCl sur la surface. La transition d'un régime à l'autre est contrôlée par l'énergie des ions du plasma. Comme le seuil de gravure en énergie est plus faible pour HfO2 que pour les substrats contenant du Si, il est possible d'obtenir une sélectivité de gravure infinie en ajustant l'énergie des ions judicieusement. De plus ce travail souligne le rôle important du conditionnement des parois du réacteur de gravure dans les mécanismes mis en jeu en plasma de BCl3. Enfin, des procédés de gravure répondant aux problèmes de sélectivité et d'anisotropie de gravure sont proposés pour graver la fine couche de HfO2 de grille.

Dy-incorporated HfO₂ gate oxide with TaN gate electrode nMOS device has been developed for high performance CMOS applications in 22nm node technology. DyO /HfO bi-layer structure shows thin EOT with reduced leakage current and less charge trapping compared to HfO₂. Excellent electrical performance of the DyO-capped HfO₂ oxide n-MOSFET such as lower V[subscript TH], higher drive current, and improved channel electron mobility are reported. DyO/HfO samples also show better immunity for V[subscript TH] instability and less severe charge trapping characteristics. Its charge trapping characteristics, conduction mechanisms and dielectric reliability have been investigated in this work. As an application to memory device, HfON charge trapping layered NAND flash memory is developed and characterized. First, temperature-dependent Dy diffusion and the diffusion-driven Dy dipole formation process are discussed to clarify the origin of V[subscript TH] shift, and eventually modulate the effective work function in Dy-Hf-O/SiO₂ system. The Dy-induced dipoles are closely related to the Dy-silicate formation at the high-k/SiO₂ interfaces since the V[subscript FB] shift in Dy₂O₃ is caused by the dipole and coincides with the Dy-silicate formation. Dipole formation is a thermally activated process, and more dipoles are formed at a higher temperature with a given Dy content. The Dy-silicate related bonding structure at the interface is associated with the strength of the Dy dipole moment, and becomes dominant in controlling the V[subscript FB]/V[scubscript TH] shift during high temperature annealing in the Dy- Hf-O/SiO₂ gate oxide system. Dy-induced dipole reduces the degradation of the electron mobility. Second, to understand the reduced leakage current of the DyO/HfO sample, the effective barrier height of Dy₂O₃ was calculated from FN tunneling models, and the band diagram was estimated. The higher effective barrier height of Dy₂O₃, which is around 2.32 eV calculated from the F-N plot, accounts for the reduced leakage current in Dy incorporated HfO₂ nMOS devices. The lower barrier height of HfO₂ result in increased electron tunneling currents enhanced by the buildup of hole charges trapped in the oxide, which causes a severe increase of stress-induced leakage current (SILC), leading to oxide breakdown. However, the increased barrier height in Dy incorporated HfO₂ inhibits a further increase of the electron tunneling from the TaN gate, and trapped holes lessen the hole tunneling currents, resulting in a negligible SILC. The lower trap generation rate by the reduced hole trap density and the reduced hole tunneling of the Dy-doped HfO₂ dielectric demonstrates the high dielectric breakdown strength by weakening the charge trapping and defect generation during the stress. Based on these fundamental studies of the dielectric breakdown, modeling of time-dependent dielectric breakdown (TDDB) was done. The intrinsic TDDB of the Dy-doped HfO₂ gate oxide having 1 nm EOT is characterized by the progressive breakdown (PBD) model. At high temperature, the PBD becomes severe, since thermal energy causes carrier hopping between the localized weak spots. The voltage acceleration factor derived from the power law shows a realistic prediction in comparison with those from the 1/E model. The increase of the voltage acceleration factor at lower stress voltage is due to the lower trap generation rate in Dy- incorporated HfO₂. This voltage acceleration factor can be easily extended to include temperature dependency, and the effective activation energy derived from the power law is voltage dependent. Lastly, I studied the device characteristics of thin HfON charge-trap layer nonvolatile memory in a TaN/Al₂O₃/HfON/SiO₂/p-Si (TANOS) structure. A large memory window and fast erase speed, as well as good retention time, were achieved by using the NH₃ nitridation technique to incorporate nitrogen into the thin HfO₂ layer, which causes a high electron-trap density in the HfON layer. The higher dielectric constant of the HfON charge-trap layer induces a higher electric field in the tunneling oxide at the same voltage compared to non-nitrided films and, thus, creates a high Fowler-Nordheim (FN) tunneling current to increase the erase and programming speed. The trap-level energy in the HfON layer was calculated by using an amphoteric model. / text

Recently, high-κ materials have become the focus of research and been extensively utilized as the gate dielectric layer in aggressive scaled complementary metal-oxide-semiconductor (CMOS) technology. Hafnium dioxide (HfO2) is the most promising high-κ material because of its excellent chemical, thermal, mechanical and dielectric properties and also possesses good thermodynamic stability and better band offsets with silicon. Hence, HfO2 has already been used as gate dielectric in modern CMOS devices. For future technologies, it is very difficult to scale the silicon transistor gate length, so it is a necessary requirement of replacing the channel material from silicon to some high mobility material. Two-dimensional layered materials such as graphene and molybdenum disulfide (MoS2) are potential candidates to replace silicon. Due to its planar structure and atomically thin nature, they suit well with the conventional MOSFET technology and are very stable mechanically as well as chemically. HfO2 plays a vital role as a gate dielectric, not only in silicon CMOS technology but also in future nano-electronic devices such as graphene/MoS2 based devices, since high-κ media is expected to screen the charged impurities located in the vicinity of channel material, which results in enhancement of carrier mobility. So, for sustenance and enhancement of new technology, extensive study of the functional materials and its processing is required. In the present work, optimization of HfO2 thin films for gate dielectric applications in Nano-electronic devices using electron beam evaporation is discussed. HfO2 thin films have been optimized in two different thickness regimes, (i) about 35 nm physical thicknesses for back gate oxide graphene/MoS2 transistors and (ii) about 5 nm physical thickness to get Equivalent Oxide Thickness (EOT) less than 1 nm for top gate applications. Optical, chemical, compositional, structural and electrical characterizations of these films have been done using Ellipsometry, X-ray Photoelectron Spectroscopy (XPS), Rutherford Back Scattering (RBS), X-ray Diffraction (XRD), Capacitance-Voltage and Current-Voltage characterization techniques. The amount of O2 flow rate, during evaporation is optimized for 35 nm thick HfO2 films, to achieve the best optical, chemical and electrical properties. It has been observed that with increasing oxygen flow rate, thickness of the films increased and refractive index decreased due to increase in porosity resulting from the scattering of the evaporant. The films deposited at low O2 flow rates (1 and 3 SCCM) show better optical and compositional properties. The effects of post deposition annealing (PDA) and post metallization annealing (PMA) in forming gas ambient (FGA) on the optical and electrical properties of the films have been analyzed. The film deposited at 3 SCCM O2 flow rate shows the best properties as measured on MOS capacitors. A high density film (ρ=8.2 gram/cm3, 85% of bulk density) with high dielectric constant of κ=19 and leakage current density of J=2.0×10-6 A/cm2 at -1 MV/cm has been achieved at optimized deposition conditions. Bilayer graphene on HfO2/Si substrate has been successfully identified and also transistor has been fabricated with HfO2 (35 nm) as a back gate. High transconductance compared to other back gated devices such as SiO2/Si and Al2O3/Si and high mobility have been achieved. The performance of back gated bilayer graphene transistors on HfO2 films deposited at two O2 flow rates of 3 SCCM and 20 SCCM has been evaluated. It is found that the device on the film deposited at 3 SCCM O2 flow rate shows better properties. This suggests that an optimum oxygen pressure is necessary to get good quality films for high performance devices. MoS2 layers on the optimized HfO2/Si substrate have been successfully identified and transistor has been fabricated with HfO2 (32 nm) as a back gate. The device is switching at lower voltages compared to SiO2 back gated devices with high ION/IOFF ratio (>106). The effect of film thickness on optical, structural, compositional and electrical properties for top gate applications has been studied. Also the effect of gate electrode material and its processing on electrical properties of MOS capacitors have been studied. EOT of 1.2 nm with leakage current density of 1×10-4 A/cm2 at -1V has been achieved.

No description available.

The current trend concerning the thinning of solar cell devices is mainly motivated by economic aspects, such as the cost of the used rare-earth elements, and by the requirements of emergent technologies. The introduction of ultra-thin absorber layers results in a reduction of used materials and thus contributes to a more cost-effective and time-efficient production process.However, the use of absorber layers with thicknesses below 500nm gives rise to multiple apprehensions, including concerns regarding light management and the absorber’s quality.Therefore, this experimental work presents a novel solar cell architecture that aims to tackle the issues of optical and electrical losses associated with ultra-thin absorber layers. To that end, a Hafnium Oxide (H f O2) rear side passivation layer was introduced in-between the copper indium gallium (di)selenide Cu(In, Ga)Se2, CIGS-based absorber layer and the Molybdenum (Mo) back contact. Then, the proposed Potassium Fluoride (KF) alkali treatment successfully established point contacts on the ALD-deposited oxide layer, resulting in a passivation effect with minimum current blockage.The established cell architecture showed significant improvements regarding both open circuit voltage (Open-Circuit Voltage (Voc)) and efficiency when compared to unpassivated reference devices. The used solar cell simulator (SCAPS) attributes the observed improvements to a reduced minority carrier recombination velocity at the rear side of the device. Moreover, the provided photoluminescence (PL) results report a higher peak intensity and lifetime for passivated devices.Furthermore, the overlay of the given external quantum efficiency (EQE) spectra with the performed simulations show that the HfO2 passivation layer improves the optical reflection from the rear contact over a wavelength interval ranging from 500 to 1100 nm, resulting in a short circuit current (Jsc) improvement. An increased quantum efficiency observed throughout almost the entire measurement range, confirms that the enhance in Jsc is also due to electronic effects.Here, a produced solar cell device including a 3nm-thick HfO2 rear passivation layer and a 500nm-thick 3-stage CIGS absorber, achieved a conversion efficiency of 9.8%.Further, the approach of combining an innovative rear surface passivation layer with a fluoride-based alkali treatment resulted in the development and successful characterisation of a 1-stage, 8.6% efficient solar cell. Such result, mainly due to a short circuit current (Jsc) enhancement, supports the introduction of more straightforward production steps, which allows a more cost-effective and time-efficient production process. The produced device consisted of a 500nm-thick CIGS absorber, rear passivated with an ultra-thin (2nm) HfO2 layer combined with a 0.6M KF treatment. / Den nuvarande trenden när det gäller solcellsanordningar huvudsakligen motiveras av ekonomiska aspekter, såsom kostnaden för att använda sällsynta jordartsmetaller, och av kraven i ny teknik. Införandet av ultratunna absorptionsskikt resulterar i en minskning av använda material och bidrar därmed till en mer kostnadseffektiv och tidseffektiv produktionsprocess.Användningen av absorptionsskikt med tjocklekar under 500 nm ger emellertid upphov till flera bekymmer, beträffande ljushantering och absorptorkvalitet.Därför presenterar detta experimentella arbete en ny solcellarkitektur som syftar till att ta itu med frågorna om optiska och elektriska förluster förknippade med ultratunna absorberlager. För detta ändamål infördes ett Hafnium Oxide (H f O2) bakre sidopassiveringsskikt mellan kopparindiumgallium (di) selenid Cu(In, Ga)Se2, CIGSbaserat absorberande skikt och Molybdenum (Mo) kontakt. Sedan upprättade den föreslagna kaliumfluorid (KF) alkali-behandlingen framgångsrikt punktkontakter på det ALD-avsatta oxidskiktet, vilket resulterade i en passiveringseffekt med minimal strömblockering.Den etablerade cellarkitektur visade signifikanta förbättringar avseende både öppna kretsspänningen (Voc) och effektivitet i jämförelse med opassiverad referensanordningar. Den använda solcellsimulatorn (SCAPS) tillskriver de observerade förbättringarna till en minskad minoritetsbärares rekombinationshastighet på enhetens baksida. Dessutom de tillhandahålls fotoluminescens (PL) resultat rapporterar en högre toppintensitet och livslängd för passive enheter.Dessutom visar överläggningen av det givna externa kvantitetseffektivitetsspektrumet (EQE) med de utförda simuleringarna att passiveringsskiktet HfO2 förbättrar den optiska reflektionen från den bakre kontakten över ett våglängdsintervall från 500 till 1100 nm, vilket resulterar i i en kortslutningsström (Jsc) förbättring. En ökad kvantverkningsgrad observerats i nästan hela mätområdet, bekräftar att öka i Jsc är också på grund av elektroniska effekter.Här, en producerad solcellsanordning innefattande en 3 nm-tjock HfO2 bakre passiveringsskikt och ett 500 nm-tjock 3-stegs CIGS absorber, uppnått en omvandlingseffektivitet på 9.8%.Vidare resulterade tillvägagångssättet att kombinera ett innovativt bakre ytpassiveringsskikt med en fluoridbaserad alkalibehandling i utvecklingen och framgångsrik karaktärisering av en 1-stegs, 8.6% effektivitet solcell. Ett sådant resultat, främst på grund av en kortslutningsström (Jsc) förbättring, stöder införandet av mer enkla produktionssteg, vilket möjliggör en mer kostnadseffektiv och tidseffektiv produktionsprocess. Den framställda anordningen bestod av ett 500 nm-tjock CIGS absorber, bakre passiverad med en ultra-tunn (2 nm) HfO2-skikt kombineras med en 0.6M KF behandling.

Cette thèse porte principalement sur la caractérisation électrique et la modélisation physique d'éléments mémoires émergents de type OxRRAM (Oxide Resistive Random Access Memory) intégrant soit un oxyde de nickel, soit un oxyde de hafnium. Une fois la maturité technologique atteinte, ce concept de mémoire est susceptible de remplacer la technologie Flash qui fait encore figure de référence. Les principaux avantages de la technologie OxRRAM reposent sur une très bonne compatibilité avec les filières CMOS, un faible nombre d'étapes de fabrication, une grande densité d'intégration et des performances attractives en termes de fonctionnement. Le premier objectif de ce travail concerne le diélectrique employé dans les cellules. Il s'agit d'apporter des éléments factuels permettant d'orienter un choix technologique sur la méthode d'élaboration de l'oxyde de nickel (oxydation thermique ou pulvérisation cathodique réactive) puis d'évaluer les performances de cellules à base d'oyxde de hafnium. Le second objectif est d'approfondir la compréhension des mécanismes physiques responsables du changement de résistance des dispositifs mémoire par une approche de modélisation physique des phénomènes opérant lors des phases d'écriture et d'effacement, sujet encore largement débattu dans la communauté scientifique. Le troisième objectif de cette thèse est d'évaluer, par le biais de caractérisations électriques, les phénomènes parasites intervenant dans les éléments mémoires de type 1R (élément résistif sans dispositif d'adressage) et, en particulier, la décharge capacitive apparaissant lors de leur programmation (opérations d'écriture). / This work is focused on the electrical characterization and physical modeling of emerging OxRRAM memories (Oxide Resistive Random Access Memory) integrating nickel or hafnium oxide. After reaching maturity, this memory concept is likely to replace the Flash technology which is still a standard in the CMOS industry. The main advantages of resistive memories technology is their good compatibility with CMOS processes, a small number of manufacturing steps, a high integration density and their attractive performances in terms of memory operation. The first objective of this thesis is to provide enough informations allowing to orientate the elaboration process of the active nickel oxide layer (thermal oxidation, reactive sputtering) then to compare the performances of the fabricated cells with devices featuring a hafnium oxide layer. The second objective is to understand the physical mechanisms responsible of the device resistance change. A physical model is proposed allowing to apprehend SET and RESET phenomenon in memory devices, subject which is still widely debated in the scientific community. The third objective of this thesis is to evaluate electrical parasitic phenomenon observed in 1R-type memory elements (resistive element without addressing device), in particular the parasitic capacitance appearing during cell programming (writing operation).

La mémoire NAND Flash représente une part importante dans le marché des circuits intégrés et a bénéficié de la traditionnelle miniaturisation de l’industrie des sémiconducteurs lui permettant un niveau d’intégration élevé. Toutefois, cette miniaturisation semble poser des sérieux problèmes au-delà du noeud 22 nm. Dans un souci de dépasser cette limite, des solutions mémoires alternatives sont proposées parmi lesquelles la mémoire résistive (RRAM) se pose comme un sérieux candidat pour le remplacement de NAND Flash. Ainsi, dans cette thèse nous essayons de répondre à des nombreuses questions ouvertes sur les dispositifs RRAM à base d’oxyde d’hafnium (HfO2) en particulier en adressant le manque de compréhension physique détaillée sur leur fonctionnement et leur fiabilité. L’impact de la réduction de taille des RRAM, le rôle des électrodes et le processus de formation et de diffusion des défauts sont étudiés. L’impact de l’alliage/dopage de HfO2 avec d’autres matériaux pour l’optimisation des RRAM est aussi abordé. Enfin, notre étude tente de donner quelques réponses sur la formation du filament conducteur, sa stabilité et sa possible composition. / Among non-volatile memory technologies, NAND Flash represents a significant portion in the IC market and has benefitted from the traditional scaling of semiconductor industry allowing its high density integration. However, this scaling seems to be problematic beyond the 22 nm node. In an effort to go beyond this scaling limitation, alternative memory solutions are proposed among which Resistive RAM (RRAM) stands out as a serious candidate for NAND Flash replacement. Hence, in this PhD thesis we try to respond to many open questions about RRAM devices based on hafnium oxide (HfO2), in particular, by addressing the lack of detailed physical comprehension about their operation and reliability. The impact of scaling, the role of electrodes, the process of defects formation and diffusion are investigated. The impact of alloying/doping HfO2 with other materials for improved RRAM performance is also studied. Finally, our study attempts to provide some answers on the conductive filament formation, its stability and possible composition.