Ultrathin Nitrided Oxide Research Articles

Modeling of nitrogen profile effects on direct tunneling probability in ultrathin nitrided oxides

The dependence of the gate tunneling current (Jg) on nitrogen profile (N profile) within an ultrathin silicon oxynitride film is reported. It was found that gate tunneling current is dependent on N profile, even with equal oxide thickness and nitrogen dosage. Gate tunneling current increased with steeper N profile, and it had higher sensitivity for p-type metal-oxide-semiconductor field-effect transistor (MOSFET) than n-type MOSFET. A direct tunneling model based on Wentzel-Kramers-Brillouin approximation has been proposed. The model described the influence of N profiles on gate tunneling current through local change of dielectric constant, band bending, and effective mass. Also, it reasonably explained the different Jg sensitivity in n-∕p-MOSFETs, a phenomenon that has not been addressed in earlier publications.

Electronic Properties of Atomic-Layer-Deposited Al[sub 2]O[sub 3]/Thermal-Nitrided SiO[sub 2] Stacking Dielectric on 4H SiC

We report the first electronic-property results on atomic-layer deposited Al 2 O 3 /thermal-nitrided SiO 2 stacking dielectric on n-type 4H SiC. The effects of the ultrathin thermal-nitrided SiO 2 (2, 4. and 6 nm) on the SiC-based metal oxide semiconductor (MOS) characteristics have also been investigated, compared, and explained. A significant improvement in dielectric reliability and dielectric breakdown field has been observed after an ultrathin nitrided oxide has been introduced between Al 2 O 3 and SiC. The best reported results were obtained from Al 2 O 3 stacked with the thickest nitrided oxide (6 nm).

Comparison of electric properties of ultra-thin thermal and plasma nitrided silicon oxides with different post-deposition treatments using C-AFM

The electrical quality of ultra-thin (∼1nm) Plasma and Thermal nitrided silicon oxide layers was investigated with Conductive AFM and a macroscopic I-V measurement setup. PN layers were found to be superior to TN layers. A longer nitridation time resulted in a better quality of the layer. Annealing in N2 was not beneficial and re-oxidation resulted in a lower leakage due to a significant increase in the physical thickness. A trap-assisted kind of tunneling was observed in these layers. The exact role of nitrogen herein is not yet well understood.

Plasma-nitrided silicon-rich oxide as an extension to ultrathin nitrided oxide gate dielectrics

We have investigated the mechanism of N incorporation, during plasma nitridation, in thermally grown ultrathin (<2nm)SiO2 films and deposited silicon-rich oxide films. X-ray photoelectron spectroscopy analysis indicates that N atoms exchange mainly with O to bond with Si atoms in ultrathin plasma-nitrided oxides. Based on this understanding, we were able to increase the amount of N that can be incorporated in plasma-nitrided silicon oxides by increasing the silicon content in these films. This was achieved by depositing ultrathin substoichiometric silicon-rich oxide films. We demonstrate an increase of almost twice as much N in these ultrathin plasma-nitrided silicon-rich oxide films yielding lower gate leakage current for a given thickness.

Enhanced negative substrate bias degradation in nMOSFETs with ultrathin plasma nitrided oxide

The degradation induced by substrate hot electron (SHE) injection in 0.13-/spl mu/m nMOSFETs with ultrathin (/spl sim/2.0 nm) plasma nitrided gate dielectric was studied. Compared to the conventional thermal oxide, the ultrathin nitrided gate dielectric is found to be more vulnerable to SHE stress, resulting in enhanced threshold voltage (V/sub t/) shift and transconductance (G/sub m/) reduction. The severity of the enhanced degradation increases with increasing nitrogen content in gate dielectric with prolonged nitridation time. While the SHE-induced degradation is found to be strongly related to the injected electron energy for both conventional oxide , and plasma-nitrided oxide, dramatic degradation in threshold voltage shift for nitrided oxide is found to occur at a lower substrate bias magnitude (/spl sim/-1 V), compared to thermal oxide (/spl sim/-1.5 V). This enhanced degradation by negative substrate bias in nMOSFETs with plasma-nitrided gate dielectric is attributed to a higher concentration of paramagnetic electron trap precursors introduced during plasma nitridation.

Model and analysis of gate leakage current in ultrathin nitrided oxide MOSFETs

An analytical model of the gate leakage current in ultrathin gate nitrided oxide MOSFETs is presented. This model is based on an inelastic trap-assisted tunneling (ITAT) mechanism combined with a semi-empirical gate leakage current formulation. The tunneling-in and tunneling-out current are calculated by modifying the expression of the direct tunneling current model of BSIM. For a microscopic interpretation of the ITAT process, resonant tunneling (RT) through the oxide barrier containing potential wells associated with the localized states is proposed. We employ a quantum-mechanical model to treat electronic transitions within the trap potential well. The ITAT current model is then quantitatively consistent with the summation of the resonant tunneling current components of resonant energy levels. The 1/f noise observed in the gate leakage current implies the existence of slow processes with long relaxation times in the oxide barrier. In order to verify the proposed ITAT current model, an accurate method for determining the device parameters is necessary. The oxide thickness and the interface trap density of the gate oxide in the 20-30 /spl Aring/ thickness range are evaluated by the quasi-static capacitance-voltage (C-V) method, dealing especially with quantum-mechanical and polysilicon effects.

Effects of thermal annealing on the electrical properties of tetraethylorthosilicate-based oxynitride films deposited on strained-Si1−xGex

We report on the effects of thermal annealing on the electrical properties of tetraethylorthosilicate (TEOS)-deposited ultra-thin nitrided oxide using nitric oxide. Ultra-thin oxynitride films have been deposited on strained Si0.82Ge0.18 layers at a low temperature by microwave plasma-enhanced chemical vapour deposition. The interface trap charge density (Dit), fixed oxide charge density (Qf/q), flatband voltage (VFB) and border trap charge (Qbt) are found to decrease with annealing up to a temperature of 800 °C. Under Fowler–Nordheim (F–N) constant current stressing, the oxynitride films show an improvement in the charge trapping behaviour after annealing. The reliability characteristics have been studied using charge-to-breakdown (QBD) measurements.

Reliability of ultrathin nitrided oxides grown in low pressure N 2O ambient

The influence of N 2O oxynitridation and oxidation pressure on reliability of ultrathin gate oxides from 4 down to 2.5 nm thickness was investigated. A set of different oxidation parameters was applied during oxide growth which comprised oxidation pressure and N 2O partial pressure during rapid thermal oxidation. The reliability of the oxides was tested by constant voltage stress. Evaluation of the resulting times to soft breakdown ( t sbd) for different stress voltages allows to predict a supply (gate) voltage V 10 y, max providing an oxide lifetime of 10 years. For this extrapolation, t sbd was assumed to increase exponentially as stress voltage is reduced. The slope of the extrapolation is found to become steeper as oxides become thinner, which implies higher V 10 y, max and thus higher reliability for thinner oxides as under an assumption of a uniform slope for all thicknesses. Further, the results of this extrapolation demonstrate that oxidation in N 2O containing ambient can improve oxide reliability for ultrathin gate oxides.

Approaching the limit for quantitative SIMS measurement of ultra-thin nitrided SiO2 films

As the demands of device performance force gate oxide thicknesses to 2nm and less, more and more pressure is placed on conventional characterization techniques to measure such thin films. Although SIMS has been utilized to accurately measure ultra-thin nitrided oxide layers for years, we are approaching the limit at which quantitative measurements can be made, simply because SIMS is a sputtering process. Measurements at a very low beam energies (300–1000eV) and incidence angles (60–80°) indicate ion mixing depths significantly less than 1nm can be achieved, with the angle of incidence being more important than the beam energy in improving depth resolution. Despite these limitations, we have achieved excellent agreement between SIMS and XPS for measurements of N areal density in 1.7–2.4nm thick films. Because the ion mixing depth is significantly less than the film thickness, SIMS can give both the distribution and amount of N within these thin layers.

Yttrium silicate formation on silicon: Effect of silicon preoxidation and nitridation on interface reaction kinetics

The effects of oxygen and nitrogen pretreatments on interface reaction kinetics during yttrium silicate formation on silicon are described. X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) are used to determine chemical bonding and composition of films formed by oxidation of yttrium deposited on silicon. Capacitance–voltage testing is used to determine the quality of the dielectric and the electrical thickness. The effect of ultrathin silicon oxide, nitrided oxide, and nitrided silicon interfaces on metal oxidation kinetics is also described. When yttrium is deposited on clean silicon and oxidized, XPS and MEIS indicate significant mixing of the metal and the silicon, resulting in a film with Y–O–Si bonding and composition close to yttrium orthosilicate (Y2O3⋅SiO2). A thin (∼10 Å) in situ preoxidation step is not sufficient to impede the metal/silicon reaction, whereas a nitrided silicon interface significantly reduces the silicon consumption rate, and the resulting film is close to Y2O3. The mechanisms described for yttrium are expected to occur in a variety of oxide and silicate deposition processes of interest for high-k dielectrics. Therefore, in addition to thermodynamic stability, understanding the relative rates of elementary reaction steps in film formation is critical to control composition and structure at the dielectric/Si interface.

Improved immunity to plasma damage in ultrathin nitrided oxides [CMOS technology

Plasma-induced damage in various 3-nm thick gate oxides (i.e., pure O/sub 2/ and N/sub 2/O-nitrided oxides) was investigated by subjecting both nMOS and pMOS antenna devices to a photoresist ashing step after metal pad definition. Gate leakage current measurements indicated that large leakage current occurs at the wafer center as well as at the wafer edge for pMOS devices, while it occurs only at the wafer center for nWOS devices. These interesting observations could be explained by the polarity dependence of ultrathin oxides in charge-to-breakdown measurements. Additionally, ultrathin N/sub 2/O-nitrided oxides show superior immunity to charging damage, especially for pMOS devices.

Growth and characterization of ultrathin nitrided silicon oxide films

This paper reviews recent progress in understanding microstructural and growth-mechanistic aspects of ultrathin (<4 nm) oxynitride films for gate dielectric applications. Different techniques for characterizing these films are summarized. We discuss several nitridation methods, including thermal (oxy)nitridation in NO, N2O, and N2 as well as a variety of deposition methods. We show that a basic understanding of the gas-phase and thin-film oxygen and nitrogen incorporation chemistries facilitates the processing of layered oxynitride nanostructures with desirable electrical properties.

Modeling boron diffusion in ultrathin nitrided oxide p/sup +/ Si gate technology

Based on a network defect model for the diffusion of B in SiO/sub 2/, we propose that B diffuses via a peroxy linkage defect (pld) whose concentration in the oxide changes under different processing conditions. We show that as N is added to the gate oxide (nitridation), N atoms compete with B atoms for activation through the diffusion-defect sites. The model predicts that nitridation is ineffective in stopping B penetration when BF/sub 2/ implants dope the polysilicon gate, as well as for the case of very thin gate dielectrics with B-implanted gates.

ChemInform Abstract: Formation of Ultrathin Nitrided SiO2 Oxides by Direct Nitrogen Implantation into Silicon.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Formation of Ultrathin Nitrided SiO2 Oxides by Direct Nitrogen Implantation into Silicon

A nitridation technique is proposed for ultrathin, oxides in deep submicron CMOS technology, which involves direct implantation of molecular nitrogen into the silicon substrate. ions were implanted into silicon at different doses and energies, through a 150 Å thick screen oxide. In this study the effect of implanted N atoms on silicon oxidation, and oxide nitridation process have been studied. Two groups of the ‐implanted wafers were used: wafers from one group were annealed prior to the screen oxide removal, whereas wafers of the other group did not receive this anneal. It is shown that nitridation can be achieved both ways, allowing this technique to be easily integrated into a semiconductor IC fabrication process.

Simplified closed-form trap-assisted tunneling model applied to nitrided oxide dielectric capacitors

Conduction has been studied in ultrathin nitrided oxide, re-oxidized nitrided oxide, and nitrogen-annealed nitrided oxide film capacitors in which the nitridation step was performed by a low-partial-pressure nitridation technique. Results indicate that, as well as some degree of barrier lowering due to the build-up of nitrogen at the injecting interface, a trap-assisted mechanism could be responsible for the enhanced conduction exhibited by the nitrided oxide devices. A simplified closed-form trap-assisted tunneling model is employed that produces a fit to the data with a trap depth of 2.1 eV. The difference between this trap model and a model requiring numerical integration was negligibly small (∼2%).

Influences of Atmospheric‐Pressure Reoxidation on the Ultrathin Oxide Films Nitrided in Atmospheric NH 3 Ambient

Effects of thermal reoxidation on the time to dielectric breakdown of ultrathin nitrided oxides have been studied. At atmospheric pressure, it was found that a proper reoxidation processing is necessary for optimizing the charge‐to‐dielectric breakdown of an arbitrarily nitrided 100Å‐thick oxide. For the more heavily nitrided oxides, a higher‐temperature or longer‐time reoxidation is required to reduce the large quantity of electron traps in the nitrided films. A superior endurance behavior with a stress current of 100 mA/cm2 was achieved for the ultrathin oxides nitrided at 900°C for 30 min and subsequently reoxidized at 950°C for 30 min as the pure oxide exhibited a charge‐to‐breakdown of 27 C/cm2with the same current density. Positive fixed charges via the nitrogen radicals or defects were shown to be the main cause of the negative flatband shift of the nitrided or reoxidized oxides.

Radiation effects in ultrathin nitrided oxides prepared by rapid thermal processing

The radiation hardness of metal-oxide semiconductor capacitors with nitrided oxides prepared by rapid thermal nitridation (RTN) has been studied. The radiation was performed by exposing devices to 50 keV x ray to a dose of 0.5 Mrad (Si). Compared to conventional thermal oxides, the rapid thermal nitrided oxide devices exhibit much less increase in the interface state density (Dit). In addition, it is found that higher RTN temperatures and/or longer durations produce smaller ΔDit. The significant reduction of the interface state generation has been attributed to the strain relief effect due to the incorporation of nitrogen at the Si/SixNyOz interface. The bond strain related models have been discussed to explain the results.

Improved radiation hardness of MOS devices with ultrathin nitrided oxide gate dielectrics prepared by rapid thermal processing

The radiation hardness of MOS devices with ultrathin nitrided oxides ( approximately 100 AA) prepared by rapid thermal nitridation (RTD) of thin oxides has been studied. The radiation was performed by exposing devices under X-rays of 50 keV to a dose of 0.5 Mrad(Si). Compared with conventional thermal oxides, the RTN oxide devices exhibit a much smaller increase in both the fixed charge N/sub f/ and the interface state D/sub it/ densities. In addition, it is found that higher RTN temperature and/or longer durations produce smaller Delta N/sub f/ and Delta D/sub it/. >

Improved transconductance under high normal field MOSFETs with ultrathin nitrided oxides

The gate-voltage dependence of electron mobility at 298 and 82 K in MOSFETs with nanometer-range thin (reoxidized) nitrided oxides prepared by rapid thermal processing (RTP) at 900-1150 degrees C for 15-300 s is discussed. Rapid nitridation improves the mobility and current derivability under high normal field over thermally grown oxides at both temperatures: the transconductance g/sub m/ at a gate drive of 3.5 V is improved by half an order of magnitude, whereas the peak g/sub m/ remains comparable to that of an oxide. Nitridation also avoids the negative g/sub m/ observed at 82 K for an oxide MOSFET. These improvements are substantially unchanged by additional reoxidations. >