Nitrided SiO2 Research Articles

Radiation-induced interface state generation in MOS devices with reoxidised nitrided SiO2 gate dielectrics

In this letter, the radiation-induced interface state generation ADh in MOS devices with reoxidised nitrided gate oxides has been studied. The reoxidised nitrided oxides were fabricated by rapid thermal reoxidation (RTO) of rapidly thermal nitrided (RTN) SiO2. The devices were irradiated by exposure to X-rays at doses of 0.5–5.0 Mrad (Si). It is found that the RTO process improves the radiation hardness of RTN oxides in terms of interface state generation. The enhanced interface ‘hardness’ of reoxidised nitrided oxides is attributed to the strainless interfacial oxide regrowth or reduction of hydrogen concentration during RTO of RTN oxides.

Study of interface state generation in thin oxynitride gate dielectrics under hot-electron stressing

The hot-electron-induced interface state generation in thin (˜8.6nm) oxynitride films prepared by rapid thermal reoxidation (RTO) of rapidly thermal nitrided (RTN) SiO2 have been studied. Both MOS capacitors and MOSFETs were used as testing devices. For MOSFETs, charge-pumping current Icp measurement was performed to monitor the increase ΔDit of interface state density. It is found that the optimised RTN and RTO processes could produce devices with a significantly improved resistance against the hotelectron- induced interface state generation.

The Influence of Processes on Composition of Thermally Nitrided SiO2 Film

The influence of process conditions, involving both oxidation and nitridation, on the results of nitridation of have been investigated. The initial oxides grown by LP, dry and wet oxidations to 200–500Å have been nitrided in either a directly heated reactor or an RF‐heated reactor. Systematic AES analyses show that by utilizing appropriate processing techniques, different distributions of nitrogen and nitrogen‐oxygen ratios can be obtained. The results demonstrate that both a low oxidation rate and a low initial nitridation rate will give a higher amount of nitrogen and a higher nitrogen‐oxygen ratio in the nitrided film. The Auger results also indicated that at the early stage of nitridation Si‐O bonds were partially broken and reactions between pure and/or partially unbonded Si and nitridizing agents had occurred. The results of post nitridation annealing show that the nitrogen in a nitrided oxide film can be further redistributed at an elevated temperature, and the nitridation reactions in the surface and bulk regions are reversible. A multilayer model is proposed to explain the kinetics of nitridation. With this model, the different nitrogen profiles and nitrogen‐oxygen ratios for different process conditions are clarified and the influence of the processes can be predicted qualitatively.

Nitridation-enhanced conductivity behavior and current transport mechanism in thin thermally nitrided SiO2

Conduction enhancement characteristics and the conduction mechanism in nitroxide are reported in this paper. Thermally grown oxides with various thicknesses were nitrided in pure ammonia for different nitridation times. Conduction in thick oxide after short-time nitridation is dominated by Fowler–Nordheim tunneling with lowered barrier height. A trap-assisted tunneling model was used to explain the effect of the degree of nitridation on current enhancement in heavily nitrided films. A theoretical calculation was carried out to fit the theory to the experimental results, and the trap density and trap energy level were found to be in the ranges of 1.2×1019–7.2×1020 cm−3 and 2.46–2.56 eV, respectively. These results are explained satisfactorily by the Auger spectroscopic data.

A STUDY ON THE PROPERTIES OF SiO2 THIN FILM THERMALLY NITRIDED IN AMMONIA AND ITS INTERFACE

The properties of thermally nitrided SiO2 thin film and its interface have been studied. It is found that the chemical composition, refractive index, electron trap parameters, surface mobility, fixed charge and interfacial state densities are dependent obviously on the annealing condition in ammonia. The mechanism of nitridation, anti-oxidation, and the effect of nitridation on interfacial characteristics are discussed.

High field phenomena in thin plasma nitrided SiO 2 films

The effects of high field tunnel electron injection on the electrical properties of Al - thin plasma nitrided SiO 2 films - Si (p-type) structures are studied. Under high field injection, it has been observed that electron trapping, positive charge generation near the Si-SiO 2 interface (slow states) and fast state generation at the Si-SiO 2 interface have taken place. After high temperature N 2 annealing, the nitridation induced electron trap density is considerably decreased. Furthermore, under high field injection the generation rate of both the slow states and the interface states and consequently, the degradation rate of the nitrided oxide films have been also decreased after annealing.

Electrical conduction in thin thermally nitrided SiO 2 (nitroxide)

Nitridation-enhanced conduction in thin nitroxide films has been examined in detail. Significant increase of high field current is attributed both to the enhanced Fowler-Nordheim (FN) tunneling injection and the Poole-Frenkel (PF) emission; the latter is confirmed by the linear dependence of log( I PF) on E 1 2 and the existence of a self-consistent dynamic dielectric constant. It is found that the enhancement of electron FN tunneling arises mainly from the piling up of nitrogen at the surface, but the PF component originates from the traps which are related to the nitrogen concentration in the bulk of nitroxide.

Charge Transport through Layers of Thermally Nitrided SiO2

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An x-ray photoelectron spectroscopy study of the thermal nitridation of SiO2/Si

X-ray photoelectron spectroscopy (XPS) has been used to study the dependence of the nitrogen distribution in thermally nitrided SiO2 films on the nitridation time and temperature. Intensity analysis of the XPS data, of which a detailed derivation is presented, in conjunction with chemical depth profiling, has been used to determine the compositional variation with depth in the nitrided film. The experimental results show that, for a nitridation temperature of 1000 °C, the maximum nitrogen concentration in the interfacial region occurs at the interface in the initial stages of nitridation (within 10 min), while at later times (30 min and longer) the maximum occurs 20–25 Å away from the interface. For a nitridation temperature of 1150 °C, the maximum interfacial nitrogen concentration occurs 20 Å from the interface for nitridation times as short as 5 min, but saturates at a lower value than that observed at 1000 °C. For a nitridation temperature of 800 °C, the maximum interfacial nitrogen concentration remains at the interface for nitridation times up to 4 h. These data can be understood within a previously developed kinetic model which explicitly considers the effect of interfacial strain on the nitridation kinetics. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen concentration. It is postulated that the fluorine bonds preferentially to defects, and it is shown that this postulate and the measured fluorine intensities are consistent with a strain-dependent energy of formation of defects, proposed recently to explain electrical results.

Strain-dependent defect formation kinetics and a correlation between flatband voltage and nitrogen distribution in thermally nitrided SiOxNy/Si structures

A correlation between the nitridation condition dependent nitrogen distribution and the magnitude of the flatband voltage shift in SiOxNy/Si structures is identified and an explanation proposed in terms of a strain-dependent kinetics of formation of defects near the interface. The proposed explanation derives from, and is consistent with, the recent demonstration of the influence of the interfacial strain on the nitridation kinetics of thermally nitrided SiOxNy/Si films.

High-temperature rapid thermal nitridation of silicon dioxide for future VLSI applications

The use of nitrided SiO 2 for very large scale integration (VLSI) applications is becoming increasingly attractive. Nitridation can convert a thin surface region of SiO 2 into a nitroxide film which is a diffusion barrier that allows the use of thin dielectrics in MOS structures and a variety of gate metals without contaminating the interfacial region. We propose a two-activation-energy model of nitridation and suggest a structure for MOS gate insulator applications. We achieved this structure using rapid thermal nitridation at 1300°C for 20 s in 1 atm. of ammonia.

Summary Abstract: Characterization of thermally nitrided SiO2 using Auger sputter profiling

Summary Abstract: Characterization of thermally nitrided SiO2 using Auger sputter profiling

Kinetics of thermal nitridation processes in the study of dopant diffusion mechanisms in silicon

The changes in diffusion rates of Sb, As, and P resulting from nitridation of SiO2 and direct nitridation of the silicon surface in NH3 ambient at 1100 °C are studied for times ranging from 7 min to 4.5 h. From analysis of these data we conclude that P must diffuse almost entirely by an interstitialcy mechanism at this temperature, and that previous formulations of dopant diffusion under nonequilibrium conditions may not be complete. We also determine that the effects seen during direct nitridation are better explained by a pure vacancy injection process than a pure self-interstitial depletion process, contrary to previous assertions by us and others.

Study of the kinetics and mechanism of the thermal nitridation of SiO2

X-ray photoelectron spectroscopy (XPS) has been used to study the nitridation time and temperature dependence of the nitrogen distribution in thermally nitrided SiO2 films. The XPS data show that the maximum nitrogen concentration near the (SiOxNy)/Si interface is initially at the interface, but moves 20–25 Å away from the interface with increasing nitridation time. Computer modeling of the kinetic processes involved is carried out and reveals a mechanism in which diffusing species, initially consisting primarily of nitrogen, react with the substrate, followed by formation of the oxygen-rich oxynitride due to reaction of the diffusing oxygen displaced by the slower nitridation of the SiO2. The data are consistent with this mechanism provided the influence of the interfacial strain on the nitridation and oxidation kinetics is explicitly accounted for.

Hydrogenation during Thermal Nitridation of SiO2

ABSTRACTThe incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000°C and for ammonia pressures of 1, 5 and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford backscattering spectrometry. Nitrogen in-depth profiles were obtained applying Auger analysis combined with ion-sputtering. Hydrogen profiles in the films were measured using nuclear reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in-depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen : measured H/N ratios varied between 0.09 and 0.85, the smaller values being obtained for the thinner oxides and higher nitridation temperatures. The model previously postulated to explain the nitrogen incorporation during atmospheric nitridation of SiO2 proves to be valid at higher pressures as well. By considering the role of OH as reaction product of the nitridation process, the hydrogen results can be accommodated within the same concept. The model predicts a low H/N incorporation ratio for a thin surface and interface layer and a substantially larger ratio for the bulk of the film. If this prediction is correct, which seems to be indicated by the etch-rate behaviour of the nitrided oxides, then this would have considerable importance for the electrical properties of this material.

Nitridation Induced-Reactions in Si and SiO2

ABSTRACTCurrent IC technology uses SiO2 almost exclusively; however, several technological and reliability problems warrant the search for an alternative dielectric. Proposed alternatives are silicon nitride and nitrided SiO2. This paper reviews the work on thermal nitridation of Si and SiO2. Several of the experimental thermal nitridation processes used to achieve good thin dielectrics are discussed. At this time a clear mechanism for the nitridation of Si is not available. The two theoretical attempts to model this process are reviewed. Innovative processes to accomplish the nitridation, such as plasma growth, etc., are presented. Finally, the influence of nitridation on stacking faults and diffusions is also reviewed.

Effect of thermally nitrided SiO2thickness on MIS characteristics

The flatband voltage of metal-insulator-semiconductor (MIS) structures with thermally nitrided SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> (nitroxide) insulators has been studied as a function of the nitroxide thickness in the range of 10-60 nm, for different nitridation conditions. The most striking result is that 10-nm nitroxide films are far less susceptible than thicker ones to the degradation of the electrical properties of the starting SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> films induced by nitridation, as revealed by a negative shift of the flatband voltage. For nitridation cycles at relatively low temperatures (900° 120 min or 1000°C 60 min) the shift in the 10-nm films is practically negligible.

X-ray photoelectron spectroscopy study of the chemical structure of thermally nitrided SiO2

X-ray photoelectron spectroscopy has been used to study the composition of 100-Å thermally grown SiO2 films that have been thermally nitrided in ammonia. The SiOxNy/Si interface was studied both by chemical depth profiling of the oxynitride and by removal of the Si substrate with XeF2. It is found that N is distributed throughout the film, but with the concentration higher at the surface and in a region centered 25 Å from the film/substrate interface. The interface region itself is found to be oxygen-rich relative to the rest of the film. Possible models which can explain these results are discussed.

Fine structure of Si LVV and N KLL Auger signals for thermally nitrided SiO 2 films

The fine structure of Si LVV and N KLL Auger signals was determined at various depths in thermally nitrided SiO 2 films. The peak near 80 eV is shifted to a slightly higher energy at the surface and at the film-silicon interface, where the nitrogen concentration is greater. It is a little lower in the interior, where the nitrogen concentration is less. The N KLL peak was shifted to a slightly higher energy at the interface than at the surface and in the interior.

Study of Electrical Characteristics on Thermally Nitrided SiO2 (Nitroxide) Films

A significant influence of thermal nitridation on the electrical characteristics of nitroxide films was found in this study. Nitridation at temperatures lower than 1000°C results in a great negative shift of flatband voltage . However, the value of continuously decreases with the increasing of nitridation time at nitridation above 1000°C. After annealing of nitroxide films in gas at 1000°C for 30 min, a decrease of , compared with the same nitridation conditions, was observed. From quasi‐static C‐V measurements, it shows that not only interface fixed charge but also surface‐state density are reduced in the decreasing of after annealing the films in gas. This effect is more prominent for nitridation at lower temperatures; however, there still exists some degree of reduction in for nitridation at higher temperature and longer time. The negative bias‐temperature instability, sometimes called “slow trapping,” is revealed by accelerated aging with negative gate bias at elevated temperatures. It is found that the instability problem is more severe for samples which are nitrided at lower temperatures but annealing can reduce the negative bias‐temperature instability. After annealing, nitroxide films prepared with nitridation above 1150°C provide good properties for MOS devices.