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The NO anneal has been shown to effectively remove 99% of defects in SiC based devices. However, the details of interactions of NO molecules with amorphous (a)-SiO2 and SiC/SiO2 interface are still poorly understood. We use DFT simulations to investigate the NO incorporation energies in a-SiO2, and how these are affected by the steric environment. The results explain the ease with which NO molecules incorporate into a-SiO2 and give an insight into the diffusion paths they take during annealing. We highlight the importance of exhaustive sampling for exploring NO diffusion pathways.

Silicon-hydrogen bonds play a crucial role in modern microelectronics, especially regarding reliability. At the semiconductor-oxide interface these bonds are broken via interaction with energetic charge carriers, which spoils a MOSFET's performance, for example. This study develops a consistent physical picture of that phenomenon through a bottom-up approach based on quantum mechanical formulations, and also unravels the disparity of that effect in $n\ensuremath{-}$ and $p\ensuremath{-}$MOSFETs. The model is free of empirical parameters and can easily be extended to emerging material combinations.

It is well-established that oxide defects adversely affect functionality and reliability of a wide range of microelectronic devices. In semiconductor-insulator systems, insulator defects can capture or emit charge carriers from/to the semiconductor. These defects feature several stable configurations, which may have profound implications for the rates of the charge capture and emission processes. Recently, these complex capture/emission events have been investigated experimentally in considerable detail in Si/SiO2 devices, but their theoretical understanding still remains vague. In this paper we discuss in detail how the capture/emission processes can be simulated using the theoretical methods developed for calculating rates of charge transfer reactions between molecules and in electro-chemistry. By employing this theoretical framework we link the atomistic defect configurations to known trapping model parameters (e.g. trap levels) as well as measured capture/emission times in Si/SiO2 devices. Using density functional theory (DFT) calculations, we investigate possible atomistic configurations for various defects in amorphous (a)-SiO2 implicated in being involved in the degradation of microelectronic devices. These include the oxygen vacancy and hydrogen bridge as well as the recently proposed hydroxyl E ′ center. In order to capture the effects of statistical defect-to-defect variations that are inevitably present in amorphous insulators, we analyze a large ensemble of defects both experimentally and theoretically. This large-scale investigation allows us to prioritize the candidates from our defect list based on their trap parameter distributions. For example, we can rule out the E ′ center as a possible candidate. In addition, we establish realistic ranges for the trap parameters, which are useful for model calibration and increase the credibility of simulation results by avoiding artificial solutions. Furthermore, we address the effect of nuclear tunneling, which is involved according to the theory of charge transfer reactions. Based on our DFT results, we demonstrate the impact of nuclear tunneling on the capture/emission process, including their temperature and field dependence, and also give estimates for this effect in Si/SiO2 devices.

We experimentally and theoretically study the impact of interface and border traps on the transfer characteristics of 4H-SiC transistors measured over a wide temperature range of 200-350 K. Quite apparently, the experimental current-voltage characteristics have drain currents which are much lower than those obtained from simulations performed without traps. Moreover, currents increase with temperature over the entire gate voltage range, while the threshold voltage shifts towards lower values as temperature increases. We show that although interface traps can explain ${I}_{{\mathrm {d}}}-{V}_{{\mathrm {gs}}}$ curves measured at room temperature with good accuracy it fails for lower temperatures. Inclusion of border traps, on the other hand, results in good agreement between experimental and simulated current-voltage characteristics over the entire temperature range. For the first time we were able to successfully represent transfer characteristics of a 4H-SiC transistor at temperatures substantially below 300 K. Therefore, we conclude that border traps are responsible for the complicated behavior of $\mathrm{I}_{{\mathrm {d}}}-\mathrm{V}_{{\mathrm {gs}}}$ characteristics.

Display Omitted HighlightsWide O-Si-O angles in bulk amorphous silica are shown to trap electrons.Trapped electron levels appear 3.2eV below the bottom of the silica conduction band.Estimated concentration of electron trapping sites is 5i?1019. Using ab initio calculations we demonstrate that extra electrons in pure amorphous SiO2 can be trapped in deep band gap states. Classical potentials were used to generate amorphous silica models and density functional theory to characterise the geometrical and electronic structures of trapped electrons. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2 and produce ? 3.2eV deep states in the band gap. These precursors comprise wide ( ? 130 ? ) O-Si-O angles and elongated Si-O bonds at the tails of corresponding distributions. The electron trapping in amorphous silica structure results in an opening of the O-Si-O angle (up to almost 180 ? ). We estimate the concentration of these electron trapping sites to be ? 5 i? 10 19 cm - 3 .

Display Omitted HighlightsHole-trapping on Si-H bond facilitates creation of neutral E ' centres.Proton released from Si-H bond has a dramatic effect on the defect's levels.A proton nearby the neutral E ' defect can facilitate electron transfer from Si substrate onto defect. Using computational modelling we investigate whether Si-H Bonds can serve as precursors for neutral E ' centre formation in amorphous silica and at the Si/SiO2 interface. Classical inter-atomic potentials are used to construct models of a-SiO2 containing Si-H bonds. We then investigate the mechanism of dissociation of a Si-H bond to create a neutral E ' defect, that is a 3-coordinated silicon with an unpaired electron localised on it. We show that the Si-H bond is extremely stable, but as a result of hole injection it is significantly weakened and may dissociate, creating a neutral E ' centre and a proton attached to one of the nearby oxygen atoms. The proton can diffuse around the E ' centre and has a profound effect on the defect levels. We show that at a Si/SiO2 interface, the position of the proton can facilitate electron transfer from the Si substrate onto the defect, making it negatively charged.

The negative bias temperature instability (NBTI) in pMOS transistors is typically assumed to consist of a recoverable (R) and a so-called permanent (P) component. While R has been studied in great detail, the investigation of P is much more difficult due to the large time constants involved and the fact that P is almost always obscured by R. As such, it is not really clear how to measure P and whether it will in the end dominate device lifetime. We address these questions by introducing a pragmatic definition of P, which allows us to collect long-term data on both large and nanoscale devices. Our results suggest that (i) P is considerably smaller than R, (ii) that P is dominated by oxide rather than interface traps and therefore (iii) shows a very similar bias dependence as R, and finally (iv) that P is unlikely to dominate device lifetime. We argue that a hydrogen-release mechanism from the gate-side of the oxide, which has been suspected to cause reliability problems for a long time [1-6], is consistent with our data. Based on these results as well as our density-functional-theory (DFT) calculations we suggest a microscopic model to project the results to operating conditions.

We used density functional theory (DFT) calculations to model the interaction of hydrogen atoms and molecules with strained bonds and neutral oxygen vacancies in amorphous silica $({\text{a-SiO}}_{2})$. The results demonstrate that the interaction of atomic hydrogen with strained Si--O bonds in defect-free ${\text{a-SiO}}_{2}$ networks results in the formation of two distinct defect structures, which are referred to as the ${[{\text{SiO}}_{4}/\text{H}]}^{0}$ and the hydroxyl ${\text{E}}^{\ensuremath{'}}$ center. To study the distribution of each defect's properties, up to 116 configurations of each center were calculated. We show that the hydroxyl ${E}^{\ensuremath{'}}$ center can be thermodynamically stable in the neutral charge state. In order to understand the origins and reactions of this defect, different mechanisms of formation, passivation, and depassivation have been investigated. The interaction of H with a single-oxygen vacancy in ${\text{a-SiO}}_{2}$ was studied in 144 configurations, all resulting in the hydrogen bridge defect. The reaction of the hydrogen bridge defect with the second H atom is barrierless and fully passivates the O vacancy. The latter defect reacts with atomic H with a small barrier, restoring the hydrogen bridge defect. These results provide a better understanding of how atomic and molecular hydrogen can both passivate existing defects and create new electrically active defects in amorphous-silica matrices.

We measure and analyse the optical absorption spectra of three silica glass samples irradiated with 1 MeV electrons at 80 K, where self-trapped holes are stable, and use ab initio calculations to demonstrate that these spectra contain a signature of intrinsic electron traps created as counterparts to the holes. In particular, we argue that optical absorption bands peaking at 3.7, 4.7, and 6.4 eV belong to strongly localised electrons trapped at precursor sites in amorphous structure characterized by strained Si–O bonds and O–Si–O angles greater than 132°. These results are important for our understanding of the properties of silica glass and other silicates as well as the reliability of electronic and optical devices and for luminescence dating.

Display Omitted We model hole trapping at hydroxyl E' centers in amorphous silicon dioxide.Two distinct hole trapping configurations: (1) Protonic configuration; (2) Back-projected configuration.Calculated barriers for transformation between both configurations.Electron trapping at these hole traps results in two distinct neutral defect configurations. We used ab initio calculations to investigate the hole trapping reactions at a neutral defect generated in amorphous silicon dioxide networks by the interaction of strained Si-O bonds with atomic hydrogen, a so-called hydroxyl E' center. It was found that the hole trapping at this defect leads to two distinct charged configurations. The first one consists of an H atom bound to a bridging O in a hydronium-like configuration. The second configuration involves relaxation of a Si atom through the plane of its oxygen neighbors facilitated by a weak interaction with a 2-coordinated O atom. The distribution of total energy differences between these two configurations calculated for a number of amorphous network models has a width of about 1.0eV. These hole trapping reactions are discussed in the context of Si complementary metal-oxide-semiconductor device reliability issues.

Hole trapping in the gate insulator of pMOS transistors has been linked to a wide range of detrimental phenomena, including random telegraph noise (RTN), 1/ f noise, negative bias temperature instability (NBTI), stress-induced leakage currents (SILC) and hot carrier degradation. Since the dynamics of hole trapping appear similar in various oxides such as pure SiO 2 , SiON, and high-k, the responsible defects should have a related microscopic structure. While a number of defects have been suspected to be responsible for these phenomena, such as oxygen vacancies/E′ centers, K centers, hydrogen bridges or hydrogen-related defects in general, the chemical nature of the dominant charge trap remains controversial. Based on extended time-dependent defect spectroscopy (TDDS) data, we investigate the statistical properties of a number of defect candidates using density functional theory (DFT) calculations. Our results suggest hydrogen bridges and hydroxyl E′ centers to be very likely candidates.

Using classical and ab initio calculations we demonstrate that extra electrons can be trapped in pure crystalline and amorphous SiO2 (a-SiO2) in deep band gap states. The structure of trapped electron sites in pure a-SiO2 is similar to that of Ge electron centers and so-called [SiO4/Li]0 centers in α quartz. Classical potentials were used to generate amorphous silica models and density functional theory to characterize the geometrical and electronic structures of trapped electrons in crystalline and amorphous silica. The calculations demonstrate that an extra electron can be trapped at a Ge impurity in α quartz in six different configurations. An electron in the [SiO4/Li]0 center is trapped on a regular Si ion with the Li ion residing nearby. Extra electrons can trap spontaneously on pre-existing structural precursors in amorphous SiO2, while the electron self-trapping in α quartz requires overcoming a barrier of about 0.6 eV. The precursors for electron trapping in amorphous SiO2 comprise wide (≥132∘) O–Si–O angles and elongated Si–O bonds at the tails of corresponding distributions. Using this criterion, we estimate the concentration of these electron trapping sites at ≈4×1019 cm−3.