Nitrogen Pile-up Research Articles

Improving the Barrier Height Uniformity of 4H—SiC Schottky Barrier Diodes by Nitric Oxide Post-Oxidation Annealing

We improved the characteristics of 4H-SiC Schottky barrier diodes (SBDs) by post-oxidation annealing in nitric oxide ambient (NO POA). Unlike the sacrificial oxidized SBDs, the SBDs with added NO POA exhibited highly uniform Schottky barrier height and nearly ideal breakdown voltage of 1990 V. Time-of-flight secondary ion mass spectroscopy revealed nitrogen pileup at the sacrificially oxidized SiC surface after NO POA. We believe that NO POA electrically passivated the detrimental residual carbon at the SiC surface by forming C-N bonds, improving the performance of the SBDs.

Bulk and interface trap generation under negative bias temperature instability stress of p-channel metal-oxide-semiconductor field-effect transistors with nitrogen and silicon incorporated HfO2 gate dielectrics

Negative bias temperature instabilities (NBTIs) of p-channel metal-oxide-semiconductor field-effect-transistor with HfO2, HfOxNy, and HfSiON were investigated. Higher bulk trap generation (ΔNot) is mainly attributed to threshold voltage shift rather than interface trap generation (ΔNit). ΔNit, ΔNot, activation energy (Ea), and lifetime were exacerbated with incorporated nitrogen while improved with adding Si into gate dielectrics. Compared to HfO2, HfOxNy showed worse NBTI due to nitrogen pile-up at Si interface. However, adding Si into HfOxNy placed nitrogen peak profile away from Si/oxide interface and NBTI was reduced. This improvement is ascribed to reduced ΔNot and ΔNit, resulting from less nitrogen at Si interface.

Performance and reliability improvements in thin-film transistors with rapid thermal N2O annealing

In the work, we applied TEOS CVD oxides as gate dielectrics for TFTs with RTN2O annealing combined with NH3 plasma passivation. This process yielded improved electrical characteristics and increased hot-carrier reliability. This is due to the nitrogen pile-up at the poly-Si/SiO2 interface and the strong Si–N bond formation that terminates the dangling bonds in the grains and at the grain boundaries in the channel region. Using the TEOS CVD oxides with rapid thermal annealing in N2O improves the TFT performance and reliability not only by densifying the deposited CVD oxide but also by incorporating the nitrogen into the gate dielectric and polysilicon channel.

Degradation Behaviors of Trigate Nanowires Poly-Si TFTs with NH[sub 3] Plasma Passivation under Hot-Carrier Stress

This work studies degradation behavior after hot-carrier stress of trigate polysilicon thin-film transistors (poly-Si TFTs) with nanowires. The NH 3 plasma passivation effect is also studied on the electrical characteristics after hot-carrier stress. The reliability of poly-Si TFTs with NH 3 plasma passivation outperforms that without such passivation, resulting from the effective hydrogen passivation of the grain-boundary dangling bonds, and the pileup of nitrogen at the SiO 2 /poly-Si interface. The reliability of poly-Si TFTs further improves by using nanowires structure. These findings originate from the fact that the nanowires poly-Si TFT has robust trigate control to reduce the hot-carrier effect due to declining lateral electrical field and its penetration from the drain, and its split nanowire structure has superior NH 3 plasma passivation effect. In degradation results under dc and ac stress, it reveals that the NH 3 plasma is mostly passivated on deep traps of grain boundaries rather than tail traps.

Effects of Channel Width and NH3 Plasma Passivation on Electrical Characteristics of Polysilicon Thin-Film Transistors by Pattern-Dependent Metal-Induced Lateral Crystallization

This work studied the effects of channel width and plasma passivation on the electrical characteristics of a series of pattern-dependent metal-induced lateral crystallization (PDMILC) polysilicon thin-film transistors (poly-Si TFTs). The performance of PDMILC TFTs improves as each channel width decreasing. Further, PDMILC TFTs with plasma passivation outperforms without such passivation, resulting from the effective hydrogen passivation of the grain-boundary dangling bonds, and the pile-up of nitrogen at the SiO2/poly-Si interface. In particular, the electrical characteristics of a nanoscale TFT with ten wide split channels (M10) are superior to those of other TFTs. The former includes a higher field effect mobility of , a higher ON/OFF current ratio , a steeper subthreshold slope (SS) of , and an absence of drain-induced barrier lowering (DIBL). These findings originate from the fact that the active channels of the M10 TFT have exhibit the most poly-Si grain enhanced to reduce the grain boundary defects and the best plasma passivation. Both effects can reduce the number of defects at grain boundaries of poly-Si in active regions for high performances.

MOS characteristics of NO-grown oxynitrides on n-type 6H-SiC

The growth of high-quality thin oxynitrides in nitric oxide (NO) ambient on n-type 6H-SiC substrate is reported. The performance and reliability of NO-grown oxynitride are compared with those of NO-annealed, N 2O-grown, N 2O-annealed and N 2-annealed oxides. NO-grown device shows the best interfacial properties and oxide reliability among all the samples. X-ray photoelectron spectroscopy analysis indicates the highest nitrogen pileup at the SiO 2/SiC interface of NO-grown sample. Therefore, the best performance of NO-grown sample can be related to the fact that oxide growth in NO has the advantage of providing higher nitrogen accumulation at the SiO 2/SiC interface and in the oxide bulk than the other growth techniques.

Electric property improvement and boron penetration suppression in metal–oxide–Si capacitors by amorphous-Si gate electrode and two-step nitridation

The improvement of electric property and reduction of boron penetration in metal–oxide–Si (MOS) capacitors are clearly achieved by the combination of a gate electrode deposited using amorphous Si(a-Si) and a gate oxynitride formed by a two-step N2O nitridation. The charge-to-breakdown performance of MOS capacitors fabricated by this technique is excellent. The hot-electron induced interface traps and flatband voltage shifts are significantly reduced. This reliability improvement can be explained in terms of a mechanism based on an increase in compressive stress (macroscopic strain) in the oxynitride and relaxation of SiO2/Si interfacial strain. Also this improvement can be due to a reduction of hydrogen-related species diffused from the gate electrode, which is achieved by nitrogen pileup at the gate electrode/oxynitride interface. Boron penetration is significantly suppressed by an a-Si gate electrode because of a larger grain size and a longer dopant diffusion path. The boron penetration is also clearly reduced by a gate oxynitride formed using a two-step N2O nitridation. Boron penetration reduction for this oxynitride can be attributed to the nitrogen incorporation into the gate electrode/oxynitride interface. This approach would be useful for the processes of gate electrode and gate dielectric in the deep submicron MOS transistors.

The impact of the nitridation process on the properties of the Si–SiO 2 interface

A newly developed technique for the simultaneous measurement of the oxide–silicon interface properties and of minority carrier lifetime in the silicon volume was used for a systematic study of the nitridation process of oxide films.This technique is based on the surface recombination velocity measurements, and does not require the formation of a capacitor structure, so it is suitable for the measurement of as-grown interface properties. Oxides grown both in dry and in wet environments were prepared, and nitridation processes in N 2O and in NO were compared to N 2 annealing processes. The effect of nitridation temperature and duration were also studied, and processes of rapid thermal oxidation (RTO) and nitridation (RTN) were compared to conventional furnace nitridation processes. Surface recombination velocity was correlated with nitrogen concentration at the oxide–silicon interface obtained by secondary ion mass spectroscopy (SIMS) measurements. Surface recombination velocity (hence surface state density) decreases with increasing nitrogen pile-up at the oxide–silicon interface, indicating that in nitrided interfaces surface state density is limited by nitridation. NO treatments are much more effective than N 2O treatments in the formation of a nitrogen–rich interface layer and, as a consequence, in interface state reduction. X-ray photoelectron spectrometry (XPS) analyses were used to extend our correlation to very thin oxides (3 nm).

Improvement of oxynitride reliability by two-step N 2O nitridation

The electrical reliability of gate oxynitride in metal-oxide-Si (MOS) capacitor can be clearly improved by the two-step N 2O nitridation. The nitridation with a low temperature and a short time could form a nitrogen pileup at the poly-Si/SiO 2 interface. It is experimentally found that the charge-to-breakdown is significantly increased and the hot-electron-induced flatband voltage shift is clearly reduced. The boron penetration effects for the pMOS devices are also suppressed. The reliability improvement can be explained by the reduction of detrimental species diffused from the poly-Si, which is achieved by nitrogen pileup at the poly-Si/SiO 2 interface. This approach would be useful for the improvement of electrical properties in the ultrathin gate oxynitrides.

Investigation of nitric oxide and Ar annealed SiO2/SiC interfaces by x-ray photoelectron spectroscopy

Silicon dioxide (SiO2)/silicon carbide (SiC) structures annealed in nitric oxide (NO) and argon gas ambiences were investigated using x-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows a nitrogen pileup of 1.6 at. % close to the NO annealed SiO2/SiC interface. The results of Si 2p, C 1s, O 1s, and N 1s core-level spectra are presented in detail to demonstrate significant differences between NO and Ar annealed samples. A SiO2/SiC interface with complex intermediate oxide/carbon states is found in the case of the Ar annealed sample, while the NO annealed SiO2/SiC interface is free of these compounds. The Si 2p spectrum of the Ar annealed sample is much broader than that of the NO annealed sample and can be fitted with three peaks compared with the two peaks in the NO annealed sample, indicating a more complex interface in the Ar annealed sample. Also the O 1s spectrum of the NO annealed samples is narrow and symmetrical and can be fitted with only one peak whereas that of the Ar annealed sample is broad and asymmetrical and is fitted with two peaks. It is evident that the Ar annealed sample contains some structural defects at the interface, which have been removed from the interface by NO annealing as shown by O 1s spectra. The C 1s spectra at the interface reveal the subtle difference between NO and Ar annealed samples. An additional peak representing the interface oxide/carbon species is observed in the Ar annealed sample. At the interface, the N 1s spectrum is symmetrical and can be fitted with one peak, representing the strong Si≡N bond. However, the N 1s and C 1s XPS spectra acquired in the bulk of the dielectric showed not only the Si≡N bond but also a trace amount of the N–C bond.

Characterization of nitrided silicon-silicon dioxide interfaces

ABSTRACTA newly-developed technique for the simultaneos characterization of the oxide-silicon interface properties and of bulk impurities was used for a systematic study of the nitridation process of thin oxides. This technique is based upon surface recombination velocity measurements, and does not require the formation of a capacitor structure, so it is very suitable for the characterization of as-grown interfaces.Oxides grown both in dry and in wet enviroments were considered, and nitridation processes in N2O and in NO were compared to N2 annealing processes. The effect of nitridation temperature and duration were also studied, and RTO/RTN processes were compared to conventional furnace nitridation processes.Surface recombination velocity was correlated with nitrogen concentration at the oxide-silicon interface obtained by Secondary Ion Mass Spectroscopy (SIMS) measurements. Surface recombination velocity (hence surface state density) decreases with increasing nitrogen pile-up at the oxide-silicon interface, indicating that in nitrided interfaces surface state density is limited by nitridation. NO treatments are much more effective than N2O treatments in the formation of a nitrogen-rich interface layer and, as a consequence, in surface state reduction.Surface state density was measured in fully processed wafers before and after constant current stress. After a complete device process surface states are annealed out by hydrogen passivation, however they are reactivated by the electrical stress, and surface state results after stress were compared with data of surface recombination velocity in as-processed wafers.

The Effect of Nitrogen in a p + Polysilicon Gate on Boron Penetration Through the Gate Oxide

Effects of nitrogen in polysilicon gates on boron penetration into a silicon substrate through the gate oxide are studied. Four factors that might be involved in how nitrogen in the polysilicon gate suppresses boron penetration were investigated: first, boron diffusivity in the interior of the nitrogen‐doped polysilicon film; second, segregation of boron at the polysilicon/ interface; third, pileup of nitrogen at the polysilicon/ interface; and fourth, boron diffusivity in decreased by incorporation of nitrogen into from polysilicon. From several experimental results, it was confirmed that the decrease in the boron diffusivity in the interior of the polysilicon gate is responsible for the suppression of boron penetration.

An innovative process sequence to obtain reliable nitrided active dielectrics

Nitrided active oxides are more and more widely used in semiconductor industry for their attractive qualities in terms of reliability and resistance to the degradation induced by current flow. Depending on the process sequence, it could happen to grow a new active dielectric in an area on which a nitrided oxide was previously grown. Nitrogen pile-up at the Si/SiO 2 interface during the nitridation process [Y. Okada et al., J. Electrochem. Soc. 140 (1993) L87; H. Fukuda et al., in: The Physics and Chemistry of SiO 2 and the Si/SiO 2 interfaces, ed. H.Z. Massoud, E.H. Poindexter and C.R. Helms (Electrochemical Society, Pennington, NJ, 1996) p. 15; D. Bouvet et al., J. Appl. Phys. 79 (1996) 7114] yields a modification of bulk Si surface characteristics, influencing the quality of the oxides grown subsequently to the nitrided oxide removal. In this paper we present an analysis of the oxide quality, reporting their properties as a function of growing techniques (i.e., whether the second oxide is nitrided or not) and of first oxide removal time (i.e., of the overetch that the Si surface experience). Exponentially ramped current stress (ERCS) and constant current stress (CCS) investigation were performed showing that to achieve a good quality of the second dielectric a further nitridation is necessary. The quality itself is strictly connected to the amount of etching of the first nitrided oxide.

Influence of Nitrogen or Argon Anneals on the Properties of Wafers and Devices Separated by Implantation of Oxygen

Wafers separated by implantation of oxygen (SIMOX) and annealed at high temperature in argon or nitrogen ambient are compared in terms of film, oxide, interface, and device properties. This evaluation is conducted by correlating pseudo‐metal‐oxide‐semiconductor field effect transistor (Ψ‐MOSFET) data in plain, unprocessed wafers with the performance of n‐ and p‐channel transistors. In situ wafer characterization with the Ψ‐MOSFET technique reveals a pileup of nitrogen near the buried interface, where the electron mobility is degraded. MOSFET characteristics are even more dramatically affected by annealing in nitrogen: large shifts of front‐ and back‐channel threshold voltages, enhanced leakage currents, and doping modification. Nitrogen‐induced donors are suspected to be responsible for doping compensation in n‐channels (leading to an unexpected full‐depletion mode of operation) and overdoping in p‐channels (reinforcing the partial depletion). By contrast to argon ambient, which does not have any major drawback, nitrogen ambient appears to be unsuitable for annealing of SIMOX wafers.

The Effects on Metal Oxide Semiconductor Field Effect Transistor Properties of Nitrogen Implantation into p+ Polysilicon Gate

We have studied in detail the effects of nitrogen implantation into a p+ polysilicon gate on gate oxide properties for the surface p-channel metal oxide semiconductor (PMOS) below 0.25 µm. The nitrided oxide film can be easily formed by the pile-up of nitrogen into the gate oxide film from the polysilicon gate. It was found that boron penetration through the gate oxide film can be effectively suppressed by nitrogen implantation into a p+ polysilicon gate because nitrogen in the polysilicon film can suppress boron diffusion, and the nitrided oxide film can also act as a barrier to boron diffusion. Moreover the hot-carrier hardness can be remarkably improved by the nitrided oxide film since interface state generation can be suppressed by the nitrided oxide film. Furthermore the number of electron traps in the gate oxide film can also be reduced by nitrogen implantation.

Effects of NH/sub 3/ plasma passivation on N-channel polycrystalline silicon thin-film transistors

The NH/sub 3/-plasma passivation has been performed on polycrystalline silicon (poly-Si) thin-film transistors (TFT's), It is found that the TFT's after the NH/sub 3/-plasma passivation achieve better device performance, including the off-current below 0.1 pA//spl mu/m and the on/off current ratio higher than 10/sup 8/, and also better hot-carrier reliability than the H/sub 2/-plasma devices. Based on optical emission spectroscopy (OES) and secondary ion mass spectroscopy (SIMS) analysis, these improvements were attributed to not only the hydrogen passivation of the defect states, but also the nitrogen pile-up at SiO/sub 2//poly-Si interface and the strong Si-N bond formation to terminate the dangling bonds at the grain boundaries of the polysilicon films. Furthermore, the gate-oxide leakage current significantly decreases and the oxide breakdown voltage slightly increases after applying NH/sub 3/-plasma treatment. This novel process is of potential use for the fabrication of TFT/LCD's and TFT/SRAM's.

Influence of Nitrogen or Argon Anneals on the Properties of Simox Wafers And Devices

AbstractSIMOX wafers annealed at high temperature in argon or nitrogen ambient are compared in terms of film, oxide, interface, and device properties. This evaluation is conducted by correlating pseudo-MOSFET data in unprocessed wafers with the performance of n- and p-channel transistors. Characterization with the Ψ-MOSFET technique reveals a pile-up of nitrogen near the buried Si -SiO2 interface, where the electron mobility is degraded. MOSFET characteristics are dramatically affected by annealing in nitrogen with large shifts of front and back channel threshold voltages, enhanced leakage currents, and channel doping modification. Nitrogen-induced donors are suspected to be responsible for doping compensation in n-channels (leading to full-depletion mode operation) and overdoping in p-channels. By contrast to argon ambient, which has no major drawbacks, nitrogen ambient can be unsuitable for annealing of SIMOX wafers.

The effects of NH3 plasma passivation on polysilicon thin-film transistors

The NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma passivation has been performed for the first time on the polycrystalline silicon (poly-Si) thin-film transistors (TFT's). It is found that the TFT's after the NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> plasma passivation achieve better device performances, including the off-current below 0.1 pA/μm and the on/off current ratio higher than 10/sup 8/, and also better hot-carrier reliability as well as thermal stability than the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -plasma devices. These improvements were attributed to not only the hydrogen passivation of the grain-boundary dangling bonds, but also the nitrogen pile-up at SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /poly-Si interface and the strong Si-N bond formation to terminate the dangling bonds at the grain boundaries of the polysilicon films.

Constructive versus destructive effects of electron beam irradiation: an application to plasma nitridation of SiO2 thin films

Low energy (3–100 eV) electrons are shown to be efficient promoters of the superficial nitridation of thin (15 nm) SiO2 films using low pure NH3 pressures (⩽2 × 10−4 mbar) at ambient temperature. The ultrahigh vacuum experimental set-up permits us to uncouple two important effects both present in a thermally-assisted (700–950 °C) r.f. NH3 plasma nitridation process: the role played by low energy (3–5 eV) electrons and the temperature. It is found that the existence of charged particles near the sample surface must be taken into account in the plasma reaction process and that the main effect of thermal activation is to enhance the reaction and the diffusion of nitrogen species through the SiO2 layer down to the SiO2/Si interface.Auger sputter depth profiles of the plasma nitrided SiO2 films have been measured before and after bombardment with energetic electrons (1, 3, or 5 keV). Electron irradiation of the film induced a nitrogen depletion at the vacuum/dielectric interface and a nitrogen pile-up at the dielectric/silicon interface. Our results indicate that this phenomenon is a maximum for the lowest primary electron energy. This behavior can be understood on the basis of an electron-stimulated Si—N bond decomposition and the creation of positive nitrogen ions. The released nitrogen ions were found to either escape in vacuum or migrate through the dielectric layer and pile-up at the dielectric/silicon interface because of the existence inside the layer of a non-uniform electric field, in agreement with recent theoretical predictions.

Electron-beam-induced nitrogen migration through a nitrided silicon dioxide thin film

Auger sputter depth profiles of very thin (15 nm) plasma-nitrided SiO 2 films thermally grown on silicon wafers have been measured before and after bombardment with energetic electrons (1, 3, or 5 keV). Electron irradiation of the film induced nitrogen depletion at the vacuum/dielectric interface and a nitrogen pile-up at the dielectric/silicon interface. Our results indicate that this phenomenon is maximum for the lowest primary electron energy. This behavior could be understood on the basis of an electron-stimulated Si-N bond decomposition and the creation of positive nitrogen ions. The released nitrogen ions could either escape into the vacuum or migrate through the dielectric layer and pile up at the dielectric/silicon interface due to the existence inside the layer of a non-uniform electric field, in agreement with recent theoretical predictions.