One of the main reliability problem in electrically erasable programmable read only memory (EEPROM) devices is the progressive closure of the programming window as the number of applied write/erase cycles is increased. This closure is qualitatively attributed to the build-up of fixed negative charge in the tunnel oxide during Fowler-Nordheim (FN) electron injection. Electron trapping induces FN current voltage shifts and consequently variations of the charge accumulated into the floating gate during one programming operation. In this work, we present an analytical quantitative model linking these shifts representative of oxide charging, to EEPROM cells threshold voltages in programmed states. This model is based on a simple electrical equivalent circuit and predicts a linear relationship between threshold and FN injection voltages shifts. The proportional constant is only dependent on the control gate-floating gate capacitive coupling ratio. Using a specific EEPROM-like test structure, the proposed model has been experimentally validated. (C) 2003 Published by Elsevier B.V.

We present a physicochemical and thermodynamic investigation of insulating thin films such as Si3N4, SiO2, etc. deposited on silicon by electric-discharge-assisted chemical vapor deposition (CVD) at moderate temperatures (T<300°C) and low pressures (P=1–2Torr). Monocrystalline silicon is treated with a SiH4+NH3 mixture in the presence of a low partial pressure of oxygen O2 (from 0 to 2%). Infrared and Auger spectroscopies were used to analyze the deposited layers. The effect of temperature and that of the presence of O2 in the mixture were examined. Thermodynamic calculations were performed to investigate the competition between simultaneous processes. The essential competition occurs between oxidation and nitridation.

In this work we have studied the influence of N2O nitridation of thin EEPROM SiO2 tunnel oxides on Fowler–Nordheim tunnel injection potential barrier heights in WSi2-polysilicon gate MOS structures. In particular we have paid attention to the effect of the nitridation temperature by means of a comparison with standard (dry-wet-dry) oxides annealed in N2 at the same temperature. The temperatures considered were 900 °C, 950 °C and 1000 °C. It has been shown that the Si/SiO2 barrier is systematically smaller than the poly-Si/SiO2 one (~0.05 eV) in the whole set of samples and that the nitridation in N2O systematically decreases both the Si/SiO2 and the poly-Si/SiO2 barrier heights all the more as the nitridation temperature increases. The effects of neglecting the contribution of Si/SiO2 interface states and of the gate depletion phenomenon in the evaluation of the oxide electric field and, as a consequence, in the evaluation of the tunnel injection potential barrier heights have also been considered. It has been shown that neglecting the polysilicon gate depletion phenomenon leads to a strongly over-evaluated value of the Si/SiO2 barrier height while neglecting the interface states gives an error of approximately 1%. Moreover, we have shown that N2O nitridation increases the oxide dielectric constant all the more as the nitridation temperature increases while fluorine incorporation into the oxide induced by the WSi2 polycide deposition process decreases the same constant.

In this work we have studied the effect of TaSi2 and WSi2 silicide deposition on the electrical properties of non-degraded dry-wet-dry oxides (similar to7.2 nm) in polycide/SiO2/Si structures. WSi2 and TaSi2 silicides are deposited by chemical vapor deposition and by sputtering respectively. Particular attention has been paid to the non-uniform density (D-it) energetical distribution of amphoter Si/SiO2 interface states, to the presence of acceptor and/or donor interface states (D-imp) due to impurities induced by the polycide gate process, and to Fowler-Nordheim (FN) barrier heights at both injecting interfaces. We have observed that i) TaSi2 structures present more important D-it densities that WSi2 ones, ii) TaSi2 samples reveal the presence of acceptor D-imp interface states probably due to SiO2 contamination by elements of the I and II groups during the silicide deposition, iii) the polycide type has a strong impact on both FN barrier heights. Finally the influence of gate oxide nitridation in N2O has been considered both in TaSi2 and WSi2 structures : i) the nitridation reduces D-it density but this reduction is more pronounced in the case of TaSi2 devices, ii) the nitridation does not reduce D-imp density in TaSi2 structures.

Boron was implanted in crystalline silicon through oxide layers with different thicknesses. The implantation is carried out at various doses and energies of interest in Ultra Large Scale Integration (ULSI) applications. Rapid thermal annealings (RTA) are used in a way to obtain shallow junctions and electrical activation of the B atoms. However, transient enhanced diffusion induced by implantation damage can be observed on boron profiles before and after annealing obtained with secondary ion mass spectrometry (SIMS). It is found that the diffusion transient in the tail region of the boron profile increases with decreasing oxide thickness. Even more, if the implantation damage concerns mostly the oxide, i.e when the concentration peak is located into this oxide, the oxygen knocked into the silicon substrate could play an important role in restricting the boron diffusion.

In microelectronics, during fabrication of ultrashallow p-n junctions boron is implanted in a silicon monocrystal, However, the subsequent rapid thermal annealing (RTA) causes anomalous fast diffusion (transient enhanced diffusion, TED) of the boron inwards in the crystal, hindering the formation of the desired ultrashallow junction. It was found that this accelerated diffusion can be overcome by applying a silica protective layer on top of the monocrystal and implanting BF2+ instead of elementary boron,This work offers a thermodynamic explanation as to why the silica layer and the presence of fluorine slow down the TED of boron, The nature, direction and magnitude of the thermodynamic forces controlling the processes are examined by two methods of approach. First, the problem is treated as the segregation-desegregation of boron at the interface, governed by excess surface Gibbs free energy of the components in the SiO2(B)-Si(B)-Si 'sandwich' structure. Second, the thermodynamic probability of solid-phase chemical interactions is considered and calculated by computer program. The effect of fluorine is treated according to its reaction with the silicon interstitials, Copyright (C) 2000 John Whey & Sons, Ltd.

Different structures, formed of polysilicon / pure oxide / mono-silicon and polysilicon nitrided oxide / mono-silicon, are realised to evaluate boron diffusion through different interfacial oxide type. So to form the p(+)-type polysilicon gate electrodes, all structures are undergone to boron implantation, under normal incidence, with doses of few 2 x 10(15) cm(-2) at 25 keV. The samples were then subjected to different rapid thermal treatments for dopant redistribution and electrical activation. The different structures are monitored using Secondary Ion Mass Spectrometry technique. The effect of the nitrided oxide is investigated and its effeciency as a boron diffusion barrier is confirmed even under important rapid thermal annealings.

Although thermal oxide remains an insulator of choice for silicon-based microelectronic devices, thin nitride and oxynitride films possess superior qualities for specific applications. In this chapter we describe both the main techniques used to manufacture thin nitrided insulator films and the main physical and electrical properties of the obtained films. The direct nitridation of silicon in ammonia, by thermal means, is difficult because it requires high temperature (> 950°C) and the obtained films are very thin (< 10 nm) because of the self-limiting nature of the growth process. Since the network of amorphous silicon nitride is denser than that of silica, it resists chemical etching (by HF solutions) better and behaves as a better barrier against diffusion. These properties are exploited in the LOCOS process. Unlike the oxide defects, the defects contained in nitrides behave mostly as electron traps. Thin oxynitride films can be fabricated by nitriding thin silica films in ammonia at high temperature (> 800°C). Nitridation may be performed at low pressure (P(NH3) < 1 mbar) or at “high” pressure (P(NH3) ≈ 1 bar). In either case, the ensuing nitrogen concentration below the surface and at the SiO2-Si interface is greater than in the bulk. The introduction of nitrogen atoms in silica, their concentration and their distribution modify in a complex fashion the physical and electrical properties of this material. The presence of nitrogen increases the dielectric strength of silica but increases the density of electron traps and introduces a hole conduction mode. It is also possible to fabricate thin oxide or nitride films, or to nitride thin silica films by using Rapid high Temperature Processes (based on the lamp heating of single wafers). The short process times used allow one to fabricate films whose properties are superior to those grown in furnace processes. To minimize the problems associated with the presence of hydrogen atoms introduced in nitrides during processing in ammonia, one can reoxidize these nitrided films. It is also possible to obtain virtually hydrogen-free nitride films by processing silicon surfaces directly in gaseous N2O or NO. The films thus obtained possess electrical properties which are superior to those of usual nitride films, and especially a greater dielectric strength and a better resistance to electrical stresses. It is also possible to fabricate nitride and oxynitride films at lower temperatures (and even at room temperature) by enhancing the reactivity of the species involved, by non-thermal means. These processes, briefly reviewed, use photons, electrons, ions or plasmas as an enhancement method, which allows one to reduce considerably the “thermal budget”. Thin nitride and oxynitride films have found numerous applications in microelectronic devices. Bien que l'oxyde thermique reste un isolant de choix pour les composants micro-électroniques sur silicium, les nitrures et les oxynitrures minces se montrent supérieurs pour certaines applications. Nous décrivons dans ce chapitre les principales techniques utilisées pour fabriquer des isolants nitrurés minces ainsi que les principales propriétés physiques et électriques des films obtenus. La nitruration directe du silicium dans l'ammoniac par voie thermique est difficile car elle nécessite de hautes températures (> 950 °C) et les films obtenus sont très minces (< 10 nm) du fait que la croissance est auto-limitée. Compte tenu de la compacité de leur réseau, les films de nitrure résistent mieux que les films d'oxyde à la gravure chimique par l'acide fluorhydrique, et constituent une barrière à la diffusion, plus efficace. Ces propriétés sont exploitées dans le procédé LOCOS. Sur le plan électrique et contrairement aux oxydes, les défauts présents dans les nitrures se comportent principalement comme des pièges à électrons. Des films minces d'oxynitrure peuvent être obtenus en nitrurant des films minces d'oxyde thermique, dans de l'ammoniac à haute température (> 800 °C). La nitruration peut s'effectuer à basse pression (P(NH3) < 1 mbar) ou à haute pression (P(NH3) ≈ 1 bar). Dans tous les cas, la concentration d'azote sous la surface et à l'interface SiO2-Si est plus grande que dans le volume. L'introduction d'azote dans la silice, sa concentration et sa distribution modifient de manière complexe les propriétés physiques et électriques de ce matériau. La présence d'azote accroît la rigidité diélectrique. Elle accroît également la densité de pièges à électron et introduit un mode de conduction par trous. Il est également possible de faire croître des films minces d'oxyde ou de nitrure ou de nitrurer des films d'oxyde en utilisant des procédés rapides à haute température (par chauffage unitaire des tranches, par lampe). Les faibles temps de traitement permettent d'obtenir des films qui ont des propriétés électriques supérieures à celles des films fabriqués dans des fours classiques. Pour minimiser les problèmes associés à la présence de l'hydrogène introduit dans les oxydes nitrurés par les traitements thermiques dans l'ammoniac, on peut réoxyder ces films. On peut également obtenir des films d'oxynitrure sans aucun hydrogène en traitant directement le silicium dans N2O ou NO. Les films ainsi obtenus présentent des propriétés électriques supérieures à celles des oxydes ou des nitrures classiques; en particulier, ils présentent une meilleure rigidité diélectrique et une très bonne résistance aux contraintes électriques. Il est également possible de fabriquer des nitrures classiques et des oxynitrures à plus basse température (voire à température ambiante) en activant les espèces réagissantes par des procédés non thermiques. Ces procédés, passés brièvement en revue, utilisent des photons, des électrons, des ions ou des plasmas comme méthode d'activation, ce qui permet de réduire considérablement le “budget thermique”. Les films minces de nitrure et d'oxynitrure de silicium ont trouvé de nombreuses applications dans les composants microélectroniques. Obwohl thermisches Oxyd hervorragende Isolatoren für die mikroelektronischen Siliziumbauelemente abgibt, werden Nitride und Oxinitride für bestimmte Anwendungen bevorzugt. In diesem Kapitel werden die wichtigsten Herstellungstechniken von isolierenden Nitriddünnschichten und deren physikalischen und elektrischen Eigenschaften erläutert. Die direkte, thermische Nitridation von Silizium in Ammoniak erweist sich als schwierig, da sie hoher Temperaturen (>950°C) bedarf und die Filmschichten sind dünn (< 10 nm) aufgrund der selbstlimitierenden Natur des Wachstumsprozesses. Durch die hohe Dichte ihres Gitters, widerstehen Nitridschichten chemischem Ätzen mit Flußsäure besser als Oxyde, sie bilden wirksamere Diffusionsgrenzen. Diese Eigenshaften werden in LOCOS-Prozeß implementiert. Was die elektrischen Eigenschaften angeht, bilden Defekte hauptsächlich Elektronenfallen, im Gegensatz zu den Oxyden. Oxinitriddünnschichten können durch Hochtemperaturnitridation (> 800°C) von thermischem Oxyd in Ammoniak hergestellt werden. Die Nitridation kann entweder bei niedrigem (P(NH3) < 1mbar) oder hohem Druck (P(NH3) ≈ 1bar) erfolgen. In beiden Fällen ist die Stickstoffkonzentration höher unter der fläche und an der SiO2-Si Grenzfläche als im Volumen. Das Einbringen von Stickstoff in Siliziumoxyd, seine Konzentration und seine Verteilung ändern die Materialeigenschaften in komplizierter Weise. Das Vorhandensein von Stickstoff verstärkt die dielektrische Eigenschaften, aber auch die Dichte der Elektronenfallen und führt zu einer Loch-Leitung. Man kann auch durch schnelle Hochtemperaturprozesse (basierend auf dem Aufheitzen durch Lampen von einzelnen Wafern) Oxid- oder Nitridschichten herzustellen oder Oxydschichten zu nitridieren. Durch die kurze Prozeßdauer, sind diese Schichten in ihren elektrischen Eigenshaften den in klassischen Öfen erzeugten Schichten überlegen. Um die Probleme, die mit dem Vorhandensein von Wasserstoff in nitridierten Oxyden verbunden sind, zu minimieren, kann man die Schichten erneut oxidieren. Oxinitridschichten ohne jeglichen Wasserstoff können auch durch unmittelbares Behandeln von Silizium mit N2O oder NO erhalten werden. Die dadurch erzeugten Schichten zeigen bessere elektrische Eigenschaften als klassische Oxyde oder Nitride, insbesondere stärkere dielektrische Eigenschaften und einen besseren Widerstand zu elektrischen Randbedingungen. Es ist auch möglich Nitride und Oxinitride bei niedrigen Temperaturen (sogar bei Raumtemperatur) herzustellen, indem man die Reaktionspartner durch nicht-thermische Mechanismen aktiviert. Diese Prozesse werden kurz beschrieben; sie verwenden Photonen, Elektronen, Ionen oder Plasmen zur Aktivierung, was das thermische “Budget” (thermischen Aufwand) wesentlich reduziert. Siliziumnitrid- und -oxinitriddünnschichten haben in mikroelektronischen Bauelementen zahlreiche Anwendungen gefunden.

The proposed work deals with rapid thermal processing of ionic boron, implanted in phosphorus-doped Cz-(100) silicon substrates through protecting oxide films, with different technological parameters. After implantation, the samples were rapidly thermally annealed at temperatures ranging from 900 to 1100 degrees C, in argon ambient gas, for different annealing durations. The rapid thermal annealings (RTA) are carried out too, for some samples, after oxide mask removing. The total boron profiles, before and after annealing steps, in the SiO2/monocrystalline silicon systems were determined using Secondary Ion Mass Spectrometry (SIMS). Using a background concentration, the junction depth in the substrate has been investigated under various annealing treatments. The diffusion process kinetic of implanted boron into oxide and monocrystalline silicon during rapid thermal treatments has been investigated too.

The present study deals with the investigation of electrically active damage induced by direct and through protecting oxide layer implantation of 11 B + ions. The residual defects have been determined by means of Deep Level Transient Spectroscopy (DLTS). It has been found that the number of defects is practically reduced to one centre when the implantation is performed through an oxide layer. The defect spectrum evolution, under the effect of the implant mass and the RTA treatments, has been also investigated. The defect generation kinetics, under annealing treatments, is found strongly depending on 11 B + ionic number reaching the substrate.

This paper reports the adaptation of charge pumping on a single DRAM cell for the in situ characterization of individual interface traps. The spatial trap distribution along the different interfaces of the DRAM cell transistor (under the gate and along the ONO/Si lateral interface) has been extensively investigated. Combining charge pumping measurements with numerical simulations allows to extract the exact trap locations.

The proposed work deals with rapid thermal processing of ionic boron (11B+) and boron difluoride (BF2+), implanted in phosphorusdoped Cz-(100) silicon substrates through protecting oxide films, under different technological parameters. After implantation, the samples were rapidly thermally annealed at temperatures ranging from 900 to 1100 °C, in argon ambient gas, for different annealing durations. The rapid thermal annealings (RTAs) are carried out also, for some samples, after oxide mask removal. The total boron, fluorine as well as oxygen concentrations versus depth profiles, before and after annealing steps, in the SiO2/Cz-(100) silicon systems were determined using secondary ion mass spectrometry (SIMS). Using a background concentration, the junction depth in the substrate has been investigated under different annealing experimental conditions. The kinetic diffusion process of implanted boron into oxide and monocrystalline silicon during rapid thermal treatments has also been investigated. The reported results show that boron diffusion in the BF2+ case is widely reduced during rapid thermal treatments. Discussions of this are based on the effect of both knocked-on oxygen and fluorine on the boron diffusion kinetics.

A novel electron cyclotron resonance plasma-enhanced chemical vapor deposition process using an alternative carbon-free source, namely TaF5, is proposed to obtain high quality amorphous Ta2O5 films. The excellent physical and electrical properties suggest that this material is clearly compatible with the requirements of high density CMOS operation, as demonstrated by the fabrication of p-channel MOS transistors with a Ta2O5 gate insulator.

Silicon MOS transistors having amorphous Ta/sub 2/O/sub 5/ insulator gates have been fabricated. The Ta/sub 2/O/sub 5/ films were deposited using a low pressure (a few mtorr) plasma-enhanced CVD process in a microwave (2.45 GHz) excited electron cyclotron resonance reactor. The source gas was TaF/sub 5/. Electrical characteristics of p-channel Al gate transistors are presented.

The effect of rapid thermal annealing (RTA) on the formation of shallow p+n junctions by the implantation of boron (11B+) and boron difluoride (BF2+) ions into SiO2Cz-(100) Si systems have been studied. The junction formation by various implant conditions have been investigated to correlate with initial dopant drive-in efficiency, defects in junctions, and junction depth under different anneal experimental conditions. Boron and fluorine concentrations versus depth profiles before and after annealing have been measured using secondary ion mass spectrometry (SIMS). Results indicate that boron diffusion in the BF2+ case is widely reduced during rapid thermal treatments. Discussions of this are based on the effect of both knocked-on oxygen and fluorine on the boron diffusion kinetics.

Boron difluoride (BF2+) ions implantation through protecting oxide films was investigated to understand the behaviour of fluorine in damaged region under rapid thermal annealing (RTA) as well as in attempt to form shallow p(+)/n junctions. The implants redistribution profiles as a function of annealing temperatures and time have been monitored by the secondary ion mass spectrometry (SIMS). Implantation induced point-defects are detected by means of deep level transient spectroscopy (DLTS) technique. The effects of both fluorine and the RTA ion-implant damage annihilation on the transient enhanced boron diffusion are investigated. In particular, the fluorine segregation behaviour near the post implantation disturbed/crystalline interface, resulting in clustering and void formation, as well as near the initial oxide/crystalline silicon is closely related to used technological data.

In this work, electrical properties of the SiSiO2 interface have been investigated in terms of interface-trap parameters (emission time, capture cross-section, state density) by standard and three-level charge pumping techniques in n-channel thin-film (8 nm) metal-oxide-semiconductor field-effect transistors. Some of the devices have been nitrided in an ammonia plasma reactor and reoxidized in oxygen. For nitrided devices, a significant decrease of interface state density, Dit, has been observed as compared with pure oxide devices. This reduction clearly corresponds to both an uniform decrease of Dit over the silicon band gap and a decrease of a Dit peak in the upper part of the band gap. The evolution of capture cross-sections has been also monitored and found to significantly vary for electron traps. This substantial change in electron interface-trap properties could be at the origin of the augmentation of the high field transconductance observed for these n-channel devices after such a nitridation process.

Ionic contamination of the oxide has been studied in Al/SiO2/3C-SiC capacitors by thermally stimulated ionic current and secondary ion mass spectroscopy analyses. Both sodium and potassium are present in the oxide. The properties of the trapping-detrapping of mobile ions in the oxide have also been studied, and two traps have been characterized. The first one is located at both the SiO2/SiC and Al/SiO2 interfaces and has an activation energy of about 1 eV. The second one is located only at the SiO2/SiC interface and is deeper (1.4 eV). The dependence of these activation energies with the electric field varies as a function of the interface and is slightly different from Al/SiO2/Si structures.

We have performed thermally stimulated ionic current measurements on aluminum-oxide-silicon carbide (3C and 6H polytypes) capacitors to study the trapping–detrapping properties of alkali mobile ions at the oxide interfaces. Two traps, at ∼1.0 and ∼1.4 eV, have been detected at the oxide/SiC interface; only one (at ∼1.0 eV) is present at the aluminum/oxide interface. Studies of the energy dependence of the oxide traps with the electric field are reported here for comparison with silicon structures. A numerical method has been used to calculate the energy distributions of these traps, which reveal some differences between the two kinds of structures.