[show abstract][hide abstract] ABSTRACT: An efficient software tool for investigations on novel stacked gate dielectrics with emphasis on reliability has been developed. The accumulation, depletion, and inversion of carriers in MOS capacitors is properly considered for n-and p-substrates. The effect of carrier quantization on the electrostatics and the leakage current is included by treating carriers in quasi-bound states (QBS) and continuum states. The effect of interface traps and bulk traps in arbitrarily stacked gate dielectrics is taken into account. Trap assisted tunneling (TAT) is incorporated assuming an inelastic single step tunneling process. A brief overview of implemented models is given. The capa-bilities of our tool are demonstrated by several examples. Ó 2007 Published by Elsevier Ltd.
[show abstract][hide abstract] ABSTRACT: Recently, an advanced model for defects in the insulating regions of semiconductor devices has been suggested, which can explain
the removable component of the negative bias temperature instability (NBTI) and recoverable random telegraph/flicker noise.
We give a brief introduction to the atomic scale physics behind the model and show how model parameters can be extracted from
density functional theory (DFT) calculations. The central link between DFT calculations and device simulation is the carrier
energy dependent part of the capture cross section, the line shape function. Calculations of the line shape functions of model
defect structures using a simple harmonic approximation are presented. The calculations show a considerable shift in the oscillator
frequency upon charge state transitions for the defects investigated.
KeywordsOxide defects-DFT-NBTI-RTS-Line shape function
Journal of Computational Electronics 04/2012; 9(3):135-140. · 1.01 Impact Factor
[show abstract][hide abstract] ABSTRACT: One of the most important degradation modes in CMOS technologies, the bias temperature instability (BTI) has been known since the 1960s. Already in early interpretations, charge trapping in the oxide was considered an important aspect of the degradation. In their 1977 paper, Jeppson and Svensson suggested a hydrogen-diffusion controlled mechanism for the creation of interface states. Their reaction-diffusion model subsequently became the dominant explanation of the phenomenon. While Jeppson and Svensson gave a preliminary study of the recovery of the degradation, this issue received only limited attention for many years. In the last decade, however, a large number of detailed recovery studies have been published, showing clearly that the reaction-diffusion mechanism is inconsistent with the data. As a consequence, the research focus shifted back toward charge trapping. Currently available advanced charge-trapping theories based on switching oxide traps are now able to explain the bulk of the experimental data. We give a review of our perspective on some selected developments in this area.
IEEE Transactions on Electron Devices 12/2011; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: The results from a recently developed measurement technique, called time-dependent defect spectroscopy (TDDS), have shed new light on reliability issues, such as random telegraph noise (RTN) and the negative bias instability (NBTI). It has been found that established models fail to explain these findings. A refined charge trapping model is suggested by assuming additional metastable defect configurations. Thereby, we can give an explanation for the new TDDS findings while remaining consistent with results obtained from conventional RTN analysis.
Noise and Fluctuations (ICNF), 2011 21st International Conference on; 07/2011
[show abstract][hide abstract] ABSTRACT: Degradation and recovery of a multi-layer high-k SiGe pMOSFET due to the negative bias temperature instability (NBTI) is modeled on the basis of a refined non-radiative multi- phonon (NMP) theory. As the SiGe-layer forms a quantum-well inside the substrate, quantum mechanical effects like subbands are incorporated into the model. In combination with a distri- bution of defects featuring different energies, barrier heights, and positions inside the oxide, a large range of accelerated stress conditions can be very accurately described. The defects accounting for the recoverable part of the NBTI degradation are finally identified as switching traps. Over the last few years the number of scientific publi- cations concerning the negative bias temperature instability (NBTI) has grown enormously. The associated controversies mostly covered the issue of the microscopic mechanism behind NBTI. The once popular reaction-diffusion model (1), (2) was eventually shown to be unable to describe the recovery after NBTI. For this reason other models have been developed, including charge trapping by either interface states and/or oxide traps (3)-(8). The latest promising attempt to model the NBTI phenomenon is based on the non-radiative multi-phonon (NMP) theory after (9), (10). It assumes the conservation of the total energy of the defect. The model has already been shown to successfully reproduce measurement data of small area devices containing only a few defects (11). In this paper, large area devices are characterized and the quantum mechanical (QM) effects in these high-k SiGe MOSFETs are incorporated into the model.
[show abstract][hide abstract] ABSTRACT: Within the theory of non-radiative multi phonon (NMP) transitions the reaction rate for an electronic transition is proportional to the product of the corresponding electronic matrix element and the line-shape function. The theory is discussed for the case of oxide traps in MOS structures. A simple method for the calculation of reaction rates for atomistic models is derived from approximations to the NMP theory. This method is applied to two selected model defects in the context of negative bias temperature instability (NBTI).
Computational Electronics (IWCE), 2010 14th International Workshop on; 11/2010
[show abstract][hide abstract] ABSTRACT: We introduce a new method to analyze the statistical properties of the defects responsible for the ubiquitous recovery behavior following negative bias temperature stress, which we term time dependent defect spectroscopy (TDDS). The TDDS relies on small-area metal-oxide-semiconductor field effect transistors (MOSFETs) where recovery proceeds in discrete steps. Contrary to techniques for the analysis of random telegraph noise (RTN), which only allow to monitor the defect behavior in a rather narrow window, the TDDS can be used to study the capture and emission times of the defects over an extremely wide range. We demonstrate that the recoverable component of NBTI is due to thermally activated hole capture and emission in individual defects with a very wide distribution of time constants, consistent with nonradiative multiphonon theory previously applied to the analysis of RTN. The defects responsible for this process show a number of peculiar features similar to anomalous RTN previously observed in nMOS transistors. A quantitative model is suggested which can explain the bias as well as the temperature dependence of the characteristic time constants. Furthermore, it is shown how the new model naturally explains the various abnormalities observed.
[show abstract][hide abstract] ABSTRACT: Due to the ongoing reduction in device geometries, the statistical properties of a few defects can significantly alter and degrade the electrical behavior of nano-scale devices. These statistical alterations have commonly been studied in the form of random telegraph noise (RTN). Here we show that a switching trap model previously suggested for the recoverable component of the negative bias temperature instability (NBTI) can more accurately describe the bias and temperature dependence of RTN than established models. We demonstrate both theoretically and experimentally, that the recovery following bias temperature stress can be considered the non-equilibrium incarnation of RTN, caused by similar defects. We furthermore demonstrate that the recoverable component is solely constituted by individual and uncorrelated discharging of defects and that no diffusive component exists. Finally it is highlighted that the capture and emission times of these defects are uncorrelated.
Electron Devices Meeting (IEDM), 2009 IEEE International; 01/2010
[show abstract][hide abstract] ABSTRACT: Our understanding of the bias temperature instability (BTI) has been plagued by disagreements related to measurement issues. Although even in the early papers on BTI the existence of recovery was acknowledged and discussed, for unknown reasons this had little impact on the way we used to think about the phenomenon until recently. Even after the re-discovery of recovery, it took a few years until it was fully appreciated that any measurement scheme conceived so far considerably interferes with the degradation it is supposed to measure, often accelerating its recovery. Nonetheless, this experimental nuisance has led researchers to think in more detail about the problem and has thus opened the floodgates for fresh ideas. Some of these ideas together with the experimental data supporting them are reviewed in the following.
[show abstract][hide abstract] ABSTRACT: Negative bias temperature instability (NBTI) is a serious reliability issue for p-channel MOSFETs when stressed with negative gate voltages at high temperatures. There is not any analytical models of NBTI reported so far, which considers the dynamics of NBTI that are commonly observed in experimental data obtained from fast measurement techniques. An analytical model for NBTI is urgently required for circuit simulation purposes. In this paper, we present an analytical solution of switching trap model, which explains the dynamics of negative bias temperature stress.
[show abstract][hide abstract] ABSTRACT: Negative Bias Temperature Instability (NBTI) is frequently suspected to arise from a delicate interplay between some sort of hole trapping and an interface generation mechanism. In a recently suggested model the E' center along with its second form as an Si - Si dimer are supposed to play a key role. Despite of its successful application to a large amount of experimental data, this model relies on a classical determination of the bandedge energy diagram and the carrier concentrations. The occurrence of subbands in the inversion layer shifts the initial energy level for charge trapping and may thus strongly impact the trapping dynamics. We evaluate the new model against measurement data in order to investigate the impact of quantization effects on the model parameters.
Simulation of Semiconductor Processes and Devices, 2009. SISPAD '09. International Conference on; 10/2009
[show abstract][hide abstract] ABSTRACT: Based on the established properties of the most commonly observed defect in amorphous oxides, the E' center, we suggest a coupled two-stage model to explain the negative bias temperature instability. 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 required to describe the first stage of degradation. In the second stage a positively charged E' center can trigger the depassivation of P<sub>b</sub> centers at the Si/SiO<sub>2</sub> interface or K<sub>N</sub> centers in oxynitrides to create an unpassivated silicon dangling bond. We evaluate the new model to experimental data obtained from three vastly different technologies (thick SiO<sub>2</sub>, SiON, and HK) and obtain very promising results.
[show abstract][hide abstract] ABSTRACT: We extend the McPherson model for the silicon–oxygen bond-breakage in a manner to capture the impact of the O–Si–O angle fluctuations (typical for amorphous SiO2) on the breakage rate. In the McPherson model the transition of the Si ion from the 4-fold coordinated position to the 3-fold coordination is considered as rupture of the Si–O bond. We have studied the potential barrier (separating these saddle points) transformation induced by the O–Si–O bond angle variations and found that the secondary minimum occurs at a critical angle of about 107.75°. Since the Si ion “finds” the way corresponding to the highest breakage probability we used the two-dimensional downhill simplex method in order to find the direction of this maximal rate. It was shown that if the O–Si–O angle deviates from its nominal value 109.48° (typical for α-quartz) corresponding to the regular SiO4 tetrahedron the symmetry aggravates and the secondary minimum is rotated. Calculated dependencies of the breakage rate on the electric field demonstrate the linear slope in the log–lin scale thus reflecting the linear reduction of the activation energy for the bond-breakage vs. field. The family of distribution functions for breakage rate calculated with a fixed step of field shows that the curves do not change their form and are shifted in parallel with the field. This tendency supports the thermo-chemical model for the bond-breakage also in the case of strongly fluctuating O–Si–O angles. As a consequence, dependencies of the mean value of the rate, its standard deviation and the nominal rate (calculated for the angle of 109.48°) have the same slope on a log–lin scale. The wide spread of the breakage rate is reflected by the high value of its standard deviation.
[show abstract][hide abstract] ABSTRACT: 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 Pb centers at the Si/ SiO2 interface or KN centers in oxynitrides to create an unpassivated silicon dangling bond. We formulate a complete model and evaluate it against experimental data.
[show abstract][hide abstract] ABSTRACT: Recent publications on negative bias temperature instability have clearly demonstrated the existence of two components contributing to the phenomenon, with one of them recovering over many timescales and the other being more or less permanent. Interestingly, these two components seem to be coupled since their effect cannot be separated by the application of different stress voltages and stress temperatures. Based on this scalability we suggest a new model which can explain the experimental data during both stress and recovery for our pure SiO<sub>2</sub>, oxynitride, and high-k devices under a wide range of experimental conditions.
[show abstract][hide abstract] ABSTRACT: We present a detailed modeling study of charging and discharging traps in dielectrics used in modern semiconductor devices. Existing descriptions of charge trapping are often restricted to charge injection from the substrate and ignore the presence of the gate contact as a source/sink of charge carriers. This assumption loses its justification when the gate dielectric shrinks into the nanometer range. Furthermore, a novel picture of tunneling into and out of defects has emerged from first principles calculations which questions the conventional concept of fixed trap levels irrespective of their charge state. Consequently, focus is put on the development of a novel rigorous model merging both effects into one general description of charge trapping.
Simulation of Semiconductor Processes and Devices, 2008. SISPAD 2008. International Conference on; 10/2008