Effect of Nitrogen Profile and Fluorine Incorporation on Negative-Bias Temperature Instability of Ultrathin Plasma-Nitrided SiON MOSFETs

The effects of plasma nitridation and fluorine incorporation on the components of negative-bias temperature instability (NBTI) in p-type MOSFETs with plasma-nitrided SiON gates were investigated. To clarify these effects, NBTI-induced threshold-voltage shift was separated into two components: one for generation of traps at the SiON/Si-substrate interface and one for positive charges within the SiON bulk. It was found that the proportions of the interface and bulk components can be controlled with the plasma nitridation method: The bulk component was increased by radio-frequency plasma nitridation, while the interface component was dominant in the case of electron-cyclotron-resonance plasma nitridation. Lowering the nitrogen concentration near the SiON/Si-substrate interface decreased the interface component. Lowering the nitrogen concentration near the poly-Si/SiON interface did not decrease NBTI, while it decreased positive oxide charges in the as-fabricated MOSFETs. Furthermore, it was demonstrated that the fluorine incorporation decreases the interface component in plasma-nitrided SiON gates, while it does not decrease the bulk component.     

Negative bias temperature instabilities in HfSiO(N)-based MOSFETs: Electrical characterization and modeling

Negative bias temperature instabilities (NBTI) in SiO_x(N)/HfSiO(N)/TaN based pMOSFETs are investigated. It is shown that nitrogen-incorporation in the gate stack (either by NH₃ anneals or decoupled plasma nitridation, DPN) result in much enhanced NBTI. Device degradation is mainly due to fast (interface) state generation in the non-nitrided stacks, while a substantial contribution of the defects produced in the nitrided stacks are slow (bulk) states. The kinetics of fast interface states is modeled within a reaction-dispersive transport model, taking into account the dispersive transport of protons generated from the depassivation of trivalent Si dangling bonds at the Si/SiO_x interace (P_b0 centers). The generation of slow states in the nitrided stacks is simulated by an electrochemical model, considering the electric field and hole assisted breaking of nitrogen-related defects, tentatively attributed to Si₂N or Hf₂N dangling bonds. A correlation between NBTI and recovery is also found, namely that enhanced NBTI in nitrided stacks results in enhanced recovery. This suggests that recovery mainly arises from the detrapping of holes at the N-related defects.     

The Impact of Nitrogen Engineering in Silicon Oxynitride Gate Dielectric on Negative-Bias Temperature Instability of p-MOSFETs: A Study by Ultrafast On-The-Fly $I_{rm DLIN}$ Technique

Degradation of p-MOSFET parameters during negative-bias temperature instability (NBTI) stress is studied for different nitridation conditions of the silicon oxynitride (SiON) gate dielectric, using a recently developed ultrafast on-the-fly I_DLIN technique having 1-mus resolution. It is shown that the degradation magnitude, as well as its time, temperature, and field dependence, is governed by nitrogen (N) density at the Si/SiON interface. The relative contribution of interface trap generation and hole trapping to overall degradation as varying interfacial N density is qualitatively discussed. Plasma oxynitride films having low interfacial N density show interface trap dominated degradation, whereas relative hole trapping contribution increases for thermal oxynitride films having high N density at the Si/SiON interface.     

Admittance spectroscopy of traps at the interfaces of (1 0 0)Si with Al2O3, ZrO2, and HfO2

Admittance (ac) measurements were carried out to determine the interface trap density (D_it) as a function of energy E in the Si bandgap at interfaces of Si with different insulating oxides (Al₂O₃, ZrO₂, HfO₂). The results are compared to those of the conventional thermal SiO₂/Si interface. The results show that a significant portion of the interface trap density in the as-deposited and de-hydrogenated samples is related to the amphoteric Si dangling bond defects (P_b0 -centers). The D_it is much enhanced for the Al-containing insulators as compared to Si/SiO₂ but can be reduced by annealing in O₂. As to annealing in H₂, efficient passivation of P_b0 centers by hydrogen is achieved for Si/ZrO₂ and Si/HfO₂ interfaces, yet it fails for Si/Al-containing oxide entities. Among the insulators studied, the results suggest HfO₂ to be the best choice of an alternative insulator.     

Applications of DCIV method to NBTI characterization

The DCIV method was applied to investigate negative bias temperature instability (NBTI) in SiO₂ gate oxides. The DCIV technique, which measures the interface defect density independently from bulk oxide charges, delineates the contribution of the interface defect generation to the overall NBTI measured by the threshold voltage shift, ΔV_TH. The DCIV results obtained during both stress and relaxation phases are generally consistent with the main features of the reaction–diffusion (R–D) model, which suggests positive charge generation/annealing at the Si/SiO₂ interface due to breaking/re-passivation of the Si–H bonds. These results are in agreement with the spin-dependent recombination (SDR) experiments, which reflect the density of the Si dangling bonds at the Si/SiO₂ interface (P_b centers) and its vicinity (E′ centers). Comparison of degradation kinetics as measured by DCIV, charge-pumping, and I_D − V_G (ΔV_TH) techniques, however, suggests that ΔV_TH includes additional contributions, most likely from the oxide bulk charges. For comparison, an NBTI study was also performed on the high-k HfO₂/SiO₂ gate stacks. After adjusting for the high-k related contribution, similar kinetics of the long-term stress interface trap generation was observed in SiO₂ and high-k gate stacks suggesting a common mechanism of the interface degradation.     

Bias temperature instabilities in 4H SiC metal oxide semiconductor field effect transistors: Insight provided by electrically detected magnetic resonance

We present insight with regard to the physical mechanisms of negative bias temperature instabilities (NBTI) in 4H SiC based metal oxide semiconductor field effect transistors (MOSFETs) based upon electrically detected magnetic resonance measurements (EDMR). Most of this insight results from EDMR studies not directly focused upon NBTI but studies more broadly focused upon two fundamental questions. (1) What as-processed defects are present at and near the SiC/oxide interface? (2) How does the presence of oxide charge alter electrically active defects at the SiC/dielectric interface? We compare the SiC results to magnetic resonance studies of bias temperature instabilities in silicon based devices. Although our analysis admittedly provides only a partial understanding of the phenomena in SiC devices, the analysis does allow for some reasonably definitive conclusions. The NBTI phenomena in 4H SiC MOSFETs are certainly different than in Si based MOSFETs. (1) Interface dangling bonds do not appear to play a significant role in SiC MOSFET interface traps under multiple circumstances, suggesting strongly that they are not significant contributors to NBTI. (2) Although oxide defects, almost certainly including the well-known E′ family of oxide traps, play an important role in SiC device NBTI, other defects, surprisingly including defects within the SiC substrate, are also involved.     

Understanding negative bias temperature instability in the context of hole trapping (Invited Paper)

Hole trapping is often considered a parasitic component clouding the real degradation mechanism that is responsible for the negative bias temperature instability (NBTI). As such, it is often dealt with in a rather sketchy way that lacks physical rigor. We review hole trapping mechanisms that go beyond the conventional elastic tunneling mechanism by including structural relaxation and field effects. Contrary to some previous studies, it is shown that the rich spectrum of experimentally observed features of the most commonly observed defect in amorphous oxides, the E′ center, is consistent with experimental data available for NBTI. In particular, we show that a full model that includes the creation of E′ centers from their neutral oxygen vacancy precursors and their ability to be repeatedly charged and discharged prior to total annealing is consistent with a first stage of degradation. In a second stage, positively charged E′ centers can trigger the depassivation of P_b centers at the Si/ SiO₂ interface or K_N centers in oxynitrides to create an unpassivated silicon dangling bond. We formulate a complete model and evaluate it against experimental data.     

Hydrogen in MOSFETs – A primary agent of reliability issues

Hydrogen plays an important role in MOSFETS as it is intentionally introduced to passivate defects (primarily Si dangling bonds) at the Si–SiO₂ interface. At the same time, hydrogen has long been known to be involved in many degradation processes, with much attention being devoted recently to bias-temperature instability (BTI). Here, we give an overview of extensive theoretical results that provide a comprehensive picture of the role that hydrogen plays in several radiation-induced degradation modes and BTI. We identify a common origin for several degradation phenomena: H is released as H⁺ by holes either in the oxide or in Si and is driven to the interface by a positive or negative bias, respectively, where it depassivates dangling bonds via the formation of H₂ molecules. We close with a note about the role of hydrogen as a main agent for aging of microelectronics.     

Effect of fluorinated silicate glass passivation layer on electrical characteristics and dielectric reliabilities for the HfO2/SiON gate stacked nMOSFET

The superior characteristics of the fluorinated hafnium oxide/oxynitride (HfO₂/SiON) gate dielectric are investigated comprehensively. Fluorine is incorporated into the gate dielectric through fluorinated silicate glass (FSG) passivation layer to form fluorinated HfO₂/SiON dielectric. Fluorine incorporation has been proven to eliminate both bulk and interface trap densities due to Hf-F and Si-F bonds formation, which can strongly reduce trap generation as well as trap-assisted tunneling during subsequently constant voltage stress, and results in improved electrical characteristics and dielectric reliabilities. The results clearly indicate that the fluorinated HfO₂/SiON gate dielectric using FSG passivation layer becomes a feasible technology for future ultrathin gate dielectrics applications.     

Negative bias temperature instability modeling for high-voltage oxides at different stress temperatures

The temperature bias instability of high-voltage oxides is analyzed. For the investigation of negative bias temperature instability (NBTI) we present an enhanced reaction–diffusion model including trap-controlled transport, the amphoteric nature of the P_b centers at the Si/SiO₂ interface, Fermi-level dependent interface charges, and fully self-consistent coupling to the semiconductor device equations. Comparison to measurement data for a stress/relaxation cycle and a wide range of temperatures shows excellent agreement.     

Hydrogen model for radiation-induced interface states in SiO2-on-Si Structures: A review of the evidence

A brief review is given of the evidence supporting the “hydrogen model” of interface trap generation in silicon-based MOS structures. Emphasis is placed on the importance of electron spin resonance (ESR) in identifying and quantifying certain crucial defect species, including atomic hydrogen, self-trapped holes, and the interface trap itself — theP _b center. Three types of experiments are considered: (1) low-temperature irradiation and isochronal anneals, (2) pulse radiolysis at room temperature, and (3) exposure of previously-irradiated devices to hydrogen gas. These disparate types of data are all reasonably accounted for by a unified model involving the production of H⁺ and/or H⁰ species in the oxide which subsequently drift to the interface where they react with hydrogen-passivated dangling bonds to formP _b centers.     

Development of an Ultrafast On-the-Fly $I_{rm DLIN}$ Technique to Study NBTI in Plasma and Thermal Oxynitride p-MOSFETs

An ultrafast on-the-fly technique is developed to study linear drain current (I _DLIN) degradation in plasma and thermal oxynitride p-MOSFETs during negative-bias temperature instability (NBTI) stress. The technique enhances the measurement resolution (ldquotime-zerordquo delay) down to 1 mus and helps to identify several key differences in NBTI behavior between plasma and thermal films. The impact of the time-zero delay on time, temperature, and bias dependence of NBTI is studied, and its influence on extrapolated safe-operating overdrive condition is analyzed. It is shown that plasma-nitrided films, in spite of having higher N density, are less susceptible to NBTI than their thermal counterparts.     

Suppression of Ge–O and Ge–N bonding at Ge–HfO2 and Ge–TiO2 interfaces by deposition onto plasma-nitrided passivated Ge substrates: Integration issues Ge gate stacks into advanced devices

A study of changes in nano-scale morphology of thin films of nano-crystalline transition metal (TM) elemental oxides, HfO₂ and TiO₂, on plasma-nitrided Ge(1 0 0) substrates, and Si(1 0 0) substrates with ultra-thin (0.8 nm) plasma-nitrided Si suboxide, SiO_x, x < 2, or SiON interfacial layers is presented. Near edge X-ray absorption spectroscopy (NEXAS) has been used to determine nano-scale morphology of these films by Jahn-Teller distortion removal of band edge d-state degeneracies. These results identify a new and novel application for NEXAS based on the resonant character of the respective O K₁ and N K₁ edge absorptions. This paper also includes a brief discussion of the integration issues for the introduction of this Ge breakthrough into advanced semiconductor circuits and systems. This includes a comparison of nano-crystalline and non-crystalline dielectrics, as well as issues relative to metal gates.     

Evidence for two distinct positive trapped charge components in NBTI stressed p-MOSFETs employing ultrathin CVD silicon nitride gate dielectric

Besides the generation of interface states and the associated positive trapped charge (N/sub tc1/), experimental results unambiguously show the generation of another positive trapped charge component (N/sub tc2/) during negative-bias temperature instability (NBTI) stressing of p-MOSFETs employing ultrathin silicon nitride gate dielectric. For a given gate stress voltage, N/sub tc2/ is generated at a much faster rate compared to N/sub tc1/. Under the pulsed gate condition studied, N/sub tc1/ could almost be completely annihilated, regardless of the NBTI stress voltage, whereas only partial annihilation of N/sub tc2/ is observed. This more resistant nature of N/sub tc2/ to post-stress relaxation has serious implications on the dynamic NBTI reliability of these p-MOSFETs.     

Detection of nitrogen incorporation in nm-thin HfO2 layers on (1 0 0)Si by electron spin resonance

We report on a low-temperature electron spin resonance (ESR) study of (1 0 0)Si/HfO₂ entities with ultrathin layers of amorphous (a)- HfO₂ deposited by distinct chemical vapor deposition (CVD) techniques using chemically different precursors. The incorporation of N is revealed in (1 0 0)Si/HfO₂ structures with ultrathin a-HfO₂ films deposited by CVD using Hf(NO₃)₄ as precursor: Upon ⁶⁰Co γ-irradiation, a prominent ESR powder pattern is observed, which via ESR measurements at two observational frequencies has been incontrovertibly identified as originating from NO₂ radicals (density 55 at ppm). The molecules are found to be stabilized and likely homogeneously distributed in the a-HfO₂ network. Based on symmetry considerations, it is suggested that during deposition, N is incorporated in the HfO₂ network as neutral N≡O₃ precursors, which are transformed into ESR-active NO₂ radicals upon γ-irradiation. The N incorporation appears inherent to the particular nitrado CVD process, an aspect that may bear on the electrical properties of the insulator, such as, e.g., introducing charge traps.     

Paramagnetic Ge dangling bond type defects at (1 0 0)Si1−xGex/SiO2 interfaces (Invited Paper)

The work addresses the occurrence of Ge dangling bond type point defects at Ge_xSi_1?x/insulator interfaces as evidenced by conventional electron spin resonance (ESR) spectroscopy. Using multifrequency ESR, we report on the observation and characterization of a first nontrigonal Ge dangling bond (DB)-type interface defect in SiO₂/(1 0 0)Ge_xSi_1?x/SiO₂/(1 0 0)Si heterostructures (0.27 ? x ? 0.93) manufactured by the condensation technique, a selective oxidation method enabling Ge enrichment of a buried epitaxial Si-rich SiGe layer. The center, exhibiting monoclinic-I (C_2v) symmetry is observed in highest densities of ～7 × 10¹² cm^?2 of Ge_xSi_1?x/SiO₂ interface for x ～ 0.7, to disappear for x outside the ]0.45–0.87[ interval, with remarkably no copresence of Si P_b-type centers. Neither are trigonal Ge DB centers observed, enabling unequivocal spectral analysis. Initial study of the defect passivation under annealing in molecular H₂ has been carried out. On the basis of all data the defect is depicted as a Ge P_b1-type center, i.e., distinct from a trigonal basic Ge P_b(0)-type center (Ge₃Ge). The modalities of the defect’s occurrence as unique interface mismatch healing defect is discussed, which may widen our understanding of interfacial DB centers in general.     

Electrical characterisation of SiON/n-Si structures for MOS VLSI electronics

In the present work, we examine the properties of SiON films grown on Si substrates by CVD in order to investigate their suitability as potential materials in replacing SiO₂ in metal-oxide-semiconductor (MOS) devices. Suitable metallization created MOS devices and electrical characterisation took place in order to identify their electrical properties. Electrical measurements included current-voltage (I-V), capacitance-conductance-voltage (C-V) measurements and admittance spectroscopy (Y−ω) allowing determination of the bulk charges and the dielectric response of the films. The analysis of the data also took into account the presence of traps at the Si/SiON interface calculated by a fast conductance technique. The interface states density was of the order of 10¹² eV⁻¹ cm⁻². The dielectric constant was found to lie between 16 and 4.5 and the corresponding bulk trapped charges were found between 8 and 113 μCb cm⁻². Post deposition annealing altered these values showing an improvement of the device behaviour. A short explanation of the above is also provided.     

Recent Issues in Negative-Bias Temperature Instability: Initial Degradation, Field Dependence of Interface Trap Generation, Hole Trapping Effects, and Relaxation

Recent advances in experimental techniques (on-the- fly and ultrafast techniques) allow measurement of threshold voltage degradation due to negative-bias temperature instability (NBTI) over many decades in timescale. Such measurements over wider temperature range (-25degC to 145degC), film thicknesses (1.2-2.2 nm of effective oxide thickness), and processing conditions (variation of nitrogen within gate dielectric) provide an excellent framework for a theoretical analysis of NBTI degradation. In this paper, we analyze these experiments to refine the existing theory of NBTI to 1) explore the mechanics of time transients of NBTI over many orders of magnitude in time; 2) establish field dependence of interface trap generation to resolve questions regarding the appropriateness of power law versus exponential projection of lifetimes; 3) ascertain the relative contributions to NBTI from interface traps versus hole trapping as a function of processing conditions; and 4) briefly discuss relaxation dynamics for fast-transient NBTI recovery that involves interface traps and trapped holes.     

The effect of NO<Subscript>2</Subscript> adsorption on optical and electrical properties of porous silicon layers

The Raman spectra and current-voltage characteristics of porous silicon layers are studied before and after exposure to NO₂. It is shown that spherical nanocrystallites with the diameter of approximately 6–8 nm are present in the samples’ structure. The effect of NO₂ brings about a decrease in the resistance of porous Si by two-three orders of magnitude. An increase in the conductance of the structures at gas concentrations as high as 2000 ppm and a drastic decrease in this conductance if the concentration exceeds the above value are observed. This effect is explained in the context of the model that implies the formation of additional defects of the type of dangling silicon bonds at the Si/SiO₂ interface as a result of oxidation of the porous silicon surface. These defects are traps for holes and reduce the increase in the hole concentration.     

Accurate negative bias temperature instability lifetime prediction based on hole injection

Negative bias temperature instability (NBTI) lifetime prediction of thin gate insulator films based on hole injection without gate voltage acceleration is described and lifetime comparison between SiO₂ film and SiON film is made based on the prediction method. The acceleration parameters are most important for the accurate lifetime prediction. The proposed acceleration parameter is not the applied voltage to the gate insulator film and the temperature but quantity of the hole injection to the gate insulator film that directly relates with the quantity of holes in the inversion layer. The degradation mechanism under the excessive voltage and excessive temperature stresses are different from that in the operation conditions. Using the hole injection method, the NBTI lifetime of SiON is less than that of SiO₂. This result agrees with the reported results measured by conventional high gate fields and temperatures. By the introduction of effective stress time (=Q_hole/J_inj0), accurate lifetime prediction in terms of the V_th shift is realized, and by analyzing of relationship between I_D reduction and V_th shift, accurate lifetime prediction in terms of the I_D reduction and the degradation prediction in the circuit level are realized. These results are essential for the accurate NBTI lifetime prediction for further more integrated LSI such as very thin gate insulator films around 1 nm.