Si-H Bond Dissociation Research Articles

The impact of self-heating and its implications on hot-carrier degradation – A modeling study

A combination of hot-carrier degradation (HCD) and self-heating (SH) was acknowledged to be the most detrimental reliability issue in ultra-scaled field-effect-transistors (FETs) with confined architectures, such as fin and nanowire (NW) FETs. Although the view on whether SH accelerates or inhibits HCD in n-channel devices is controversial, it is commonly accepted that in p-channel FETs HCD becomes more pronounced due to SH. Therefore, we develop a framework for modeling coupled HCD and SH and validate it against experimental data acquired in p-channel Si NWFETs. This framework incorporates a carrier transport solver linked to a solver for the lattice heat flow equation; the latter solver allows one to evaluate a non-uniform lattice temperature distribution in the device. Carrier energy distribution functions obtained considering coordinate-dependent lattice temperature are used to calculate the rates of the multiple- and single-carrier processes of SiH bond dissociation. In addition to perturbation of carrier transport by SH, elevated lattice temperature results in enhancement of the thermal contribution to the bond rupture rate and shortens vibrational lifetime of the SiH bond, thereby reducing the multiple-carrier process rate. All these three aspects are captured by our framework, importance of each of them is analyzed, and our approach was shown to accurately reproduce experimental data.

Polymerization of silanes through dehydrogenative Si-Si bond formation on metal surfaces.

Element-element double bonds of group 14 elements can be formed in solution, but generally only by applying harsh reductive conditions using sterically highly shielded tetryl halides as precursors. The two-dimensional confinement in surface-assisted polymerization represents a valuable alternative to access such reactive compounds, as it allows shielding of the labile entities without requiring bulky residues and catalytic activation of the reactive groups. Here, we demonstrate Si-Si bond formation in on-surface chemistry. Polymerization upon multiple Si-H bond dissociation and subsequent Si-Si bond formation was achieved on Au(111) and Cu(111) surfaces by using two different monomers, each containing two silicon functional groups (CH3SiH2 or SiH3) attached to an aromatic backbone, leading to polymeric disilenes that interact with the surface. A combination of experimental and theoretical studies corroborates the formation of covalent Si-Si bonds between the long, highly ordered polymer chains with high diastereoselectivity. The reactive Si=Si bonds formally generated via double dehydrogenative coupling are stabilized via covalent Si-surface interaction.

Energetic ion induced desorption of hydrogen from porous silicon studied by on-line elastic recoil detection analysis

We report a detailed study on the concentration profiles and ion irradiation induced desorption of hydrogen from porous silicon (pSi) by on-line elastic recoil detection analysis (ERDA). 100 MeV Ag ions have been employed to analyze the pSi samples prepared at different etching current densities. The observed blue shift in the photoluminescence of pSi with increase in etching current density is consistent with previous reports. Here we find that the concentration of hydrogen in near surface regions decreases with increase in etching current density. It is also observed that the concentration of hydrogen is greater in the near surface region and decreases rapidly as a function of depth in porous silicon. Further, the ion irradiation induced desorption of hydrogen from pSi has been characterized by the second order decay, indicating that the hydrogen desorbs in molecular form. The rate of desorption is found to be higher from the deeper layers when compared to that of near-surface regions, possibly due to higher diffusivity of elemental hydrogen within the deeper layer. Strong electronic excitations produced by probing beam are expected to be responsible for the observed non-thermal dissociation of SiH bonds and consequent desorption of hydrogen from the surface of pSi in molecular form. These results provide useful information to elucidate 1) the role of hydrogen in determining the optical properties of porous/nano-crystalline silicon and 2) mechanisms that govern the non-thermal dissociation of SiH bonds.

Electron-electron scattering-induced channel hot electron injection in nanoscale n-channel metal-oxide-semiconductor field-effect-transistors with high-k/metal gate stacks

This work investigates electron-electron scattering (EES)-induced channel hot electron (CHE) injection in nanoscale n-channel metal-oxide-semiconductor field-effect-transistors (n-MOSFETs) with high-k/metal gate stacks. Many groups have proposed new models (i.e., single-particle and multiple-particle process) to well explain the hot carrier degradation in nanoscale devices and all mechanisms focused on Si-H bond dissociation at the Si/SiO2 interface. However, for high-k dielectric devices, experiment results show that the channel hot carrier trapping in the pre-existing high-k bulk defects is the main degradation mechanism. Therefore, we propose a model of EES-induced CHE injection to illustrate the trapping-dominant mechanism in nanoscale n-MOSFETs with high-k/metal gate stacks.

Predictive Hot-Carrier Modeling of n-Channel MOSFETs

We present a physics-based hot-carrier degradation (HCD) model and validate it against measurement data on SiON n-channel MOSFETs of various channel lengths, from ultrascaled to long-channel transistors. The HCD model is capable of representing HCD in all these transistors stressed under different conditions using a unique set of model parameters. The degradation is modeled as a dissociation of Si-H bonds induced by two competing processes. It can be triggered by solitary highly energetical charge carriers or by excitation of multiple vibrational modes of the bond. In addition, we show that the influence of electron-electron scattering (EES), the dipole-field interaction, and the dispersion of the Si-H bond energy are crucial for understanding and modeling HCD. All model ingredients are considered on the basis of a deterministic Boltzmann transport equation solver, which serves as the transport kernel of a physics-based HCD model. Using this model, we analyze the role of each ingredient and show that EES may only be neglected in long-channel transistors, but is essential in ultrascaled devices.

Defect Generation Mechanism and Its Impact on Reliability Properties in MONOS Devices

Introduction Metal-oxide-nitride-oxide-semiconductor (MONOS) device attracts much attention owing to its potential as future nonvolatile memory devices. For the use of MONOS devices, it is important to understand accurately the mechanism of reliability degradation induced by electrical stress such as programming and erasing. In this paper, we discuss the defects-generation mechanisms by using evaluation technique that we developed. We also show how the defects generation influences to reliability properties of the MONOS devices. Interface-State Generation by Program/Erase Cycling Program/Erase (P/E) cycle stress generates defects in MONOS devices and degrades their performance and reliability. Since it has been recognized for the MONOS devices that the degradation is mainly due to interface-state generation, we examined the mechanism of interface-state generation in the MONOS devices under P/E stress by using a charge measurement technique we developed. The amount of interface states (ΔNit) is found to have a strong correlation with charges flowing during erasing, irrespective of pulse voltage, pulse width and number of P/E cycles. It is further demonstrated that the ΔNit increases as hole current dominates in erasing, suggesting that hole injection from Si substrate during erasing is the main cause for the ΔNit. Data Retention Degradation Caused by Stress Induced Hole Current Data retention measurements after P/E cycle stress were carried out with applying gate voltage to control the direction of electron leakage during retention. As a result, higher charge loss was observed when applying negative gate voltage during retention, indicating that P/E stress-induced leakage current (SILC) across the tunnel oxide layer degrades the data retention.To detect the SILC directly, we performed carrier separation I-V measurement for p-channel MONOS devices. The tail of electron detrapping current at low voltage (electron SILC) was, however, observed only for the MONOS with highly Si-rich SiN charge trapping layer. Thus, a mechanism other than the electron SILC must be involved in the data retention degradation for the MONOS devices. The carrier separation measurements further demonstrated that hole current injected into the MONOS devices is increased after P/E cycle stress, indicating the existence of “hole SILC”. The hole SILC is found to be determined by the ΔNit regardless of MONOS structure, suggesting that the hole SILC is attributable to the generated interface states. These results suggest a mechanism for the data retention degradation caused by P/E cycle stress: The P/E cycle stress damages tunnel oxide layer and generates the ΔNit. The hole SILC is injected via the ΔNit, degrading data retention through hole trapping and possible subsequent recombination with stored electrons. Impact of Interface-State Recovery on Reliability Properties It is well known, in the research field of MOS reliability, that accumulated holes attack Si-H bonds at the Si/SiO2 interface and induce negative bias temperature instability (NBTI). Since the ΔNit in the MONOS devices is generated by holes accumulated in Si substrate, it is speculated that physical origin of the ΔNit is similar to that in MOS devices, that is, Si-H bond dissociation. The Reaction-Diffusion (R-D) model, which explains well the NBTI mechanism, suggests that hydrogen released by the Si-H dissociation diffuses back to the interface and passivates the generated interface states after removal of electrical stress. It was observed for the MONOS devices that the ΔNit was found to be decreased after 200ºC 1h baking, demonstrating that the ΔNit is due to dissociation of Si-H bonds. Since the recovery accompanies the threshold voltage shift, suppression of the ΔNit is important for data retention property as well as for endurance property. Conclusions We have investigated the mechanisms for interface-state generation by P/E cycle stress, and demonstrated that holes injected from Si substrate is the main cause for the ΔNit. It is also found that the hole SILC is injected via the ΔNit, degrading data retention property through hole trapping and possible subsequent recombination with stored electrons. Since the physical origin of the ΔNit is Si-H bond breakage, a part of released hydrogen diffuses back to the interface and passivates the ΔNit, leading to the degradation of data retention property.

Are Interface State Generation and Positive Oxide Charge Trapping Under Negative-Bias Temperature Stressing Correlated or Coupled?

Studies have suggested that interface state generation under negative-bias temperature (NBT) stress results in positive oxide charge trapping. The latter is ascribed to the trapping of hydrogen species, from Si-H bond dissociation, in the oxide bulk. In this paper, we present evidence from dynamic NBT instability showing no apparent relationship between the two degradation mechanisms. The level of positive oxide trapped charge is shown to remain constant despite a nonnegligible increase of threshold voltage <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> shift due to interface state generation. This observation implies that Si-H bond dissociation did not result in any significant positive oxide trapped charge, and that the latter is due to a different mechanism (e.g., hole trapping at oxygen vacancies). The inference is supported by results from channel hot-hole stress, which is known to dissociate Si-H bonds but did not increase the level of positive oxide trapped charge. Possible reasons for the difference between previous and current studies are discussed. We also examine the observation on the “universal scalability” of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> drift curves from different stress conditions, as explained by <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">'</sup> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">b</sub> coupling, i.e., Si-H bond dissociation is driven by hole trapping at nearby oxygen vacancies. We revisit an earlier observation that shows that such scalability only holds in the initial stage when positive oxide charge trapping is dominant, and that the scaled <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> drift curves eventually diverge in the later stage. Further evidence shows that the divergence is caused by interface state generation proceeding at a faster rate compared to positive oxide charge trapping. The result confirms that a part of interface degradation proceeds independently of positive oxide charge trapping.

Adsorption and surface reaction of bis-diethylaminosilane as a Si precursor on an OH-terminated Si (0 0 1) surface

The adsorption and the surface reaction of bis-diethylaminosilane (SiH2[N(C2H5)2]2, BDEAS) as a Si precursor on an OH-terminated Si (001) surface were investigated to understand the initial reaction mechanism of the atomic layer deposition (ALD) process using density functional theory. The bond dissociation energies between two atoms in BDEAS increased in the order of SiH, SiN, and the rest of the bonds. Therefore, the relatively weak SiH and SiN bonds were considered for bond breaking during the surface reaction. Optimum locations of BDEAS for the SiH and SiN bond breaking were determined on the surface, and adsorption energies of 0.43 and 0.60eV, respectively, were obtained. The SiH bond dissociation energy of the adsorbed BDEAS on the surface did not decrease, so that a high reaction energy barrier of 1.60eV was required. On the other hand, the SiN bond dissociation energy did decrease, so that a relatively low reaction energy barrier of 0.52eV was required. When the surface reaction energy barrier was higher than the adsorption energy, BDEAS would be desorbed from the surface instead of being reacted. Therefore, the SiN bond breaking would be dominantly involved during the surface reaction, and the result is in good agreement with the experimental data in the literature.

Tris(trimethylsilyl)silane (TTMSS)

Tris(trimethylsilyl)silane (TTMSS) has been used in many transformations, especially in radical chain reactions. Chatgilialoglu et al. demonstrated that this reagent can be a valuable substitute for tin reagents commonly used in radical processes. [1] The Si-H bond dissociation ­energy in TTMSS of 79 kcal·mol-1 is very similar to the Sn-H bond dissociation energy of 74 kcal·mol-1 in Bu3SnH. [2] The ease of purification and the low toxicity of TTMSS make it an attractive alternative to tin as a ­reducing agent. Interestingly, there are also reports ­demonstrating that the behavior of TTMSS can be very different from that of tin hydrides. [3]

Mechanism of Dynamic Bias Temperature Instability in p- and nMOSFETs: The Effect of Pulse Waveform

The waveform effect on dynamic bias temperature instability (BTI) is systematically studied for both p- and nMOSFETs with ultrathin SiON gate dielectrics by using a modified direct-current current-voltage method to monitor the stress-induced interface trap density. Interface traps are generated at the inversion gate bias (negative for pMOSFETs and positive for nMOSFETs) and are partially recovered at the zero or accumulation gate bias. Devices under high-frequency bipolar stress exhibit a significant frequency-dependent degradation enhancement. Approximate analytical expressions of the interface trap generation for devices under the static, unipolar, or bipolar stress are derived in the framework of conventional reaction-diffusion (R-D) model and with an assumption that additional interface traps (Nit *) are generated in each cycle of the dynamic stress. The additional interface trap generation is proposed to originate from the transient trapped carriers in the states at and/or near the SiO2/Si interface upon the gate voltage reversal from the accumulation bias to the inversion bias quickly, which may accelerate dissociation of Si-H bonds at the beginning of the stressing phase in each cycle. Hence, N it * depends on the interface-state density, the voltage at the relaxation (i.e., accumulation) bias, and the transition time of the stress waveform (the fall time for pMOSFETs and the rise time for nMOSFETs). The observed dynamic BTI behaviors can be perfectly explained by this modified R-D model

Structure, energetics, and vibrational properties of Si-H bond dissociation in silicon

We investigate hydrogen dissociation from an isolated Si-H bond in bulk silicon, using ab initio density- functional total-energy calculations. From the bonding site, we find that hydrogen needs to overcome a barrier of less than 2.0 eV in order to reach the next lowest local minimum in the energy surface. This minimum occurs at the antibonding site and is 1.2 eV higher in energy than the ground state. In addition, we consider the role of lattice relaxations and free carriers during the dissociation process. We discuss the relevance of our results for Si-H dissociation in several systems, including the Si-SiO 2 interface. @S0163-1829~99!05919-6# passivating the dangling bond, forming a strong Si-H bond. An additional local minimum is found for hydrogen at the antibonding site ~i.e., behind the Si atom, on the other side of the dangling bond!. Compared to hydrogen in the bonding site, hydrogen in the antibonding site has an energy 1.2 eV higher, an Si-H bond length ;3% longer and an Si-H stretch-mode frequency which is 180 cm 21 lower. When hy- drogen is trapped in the antibonding site, electronic levels are introduced into the gap allowing for carrier-enhanced Si-H dissociation. The saddle point for migration from the dangling bond to the antibonding site occurs at the bond- center site, with a migration barrier of 1.75 eV. Large lattice relaxations are required for the H atom to approach the bond- center site; the kinetics of Si-H dissociation through the bond-center site will thus be tied to silicon-silicon vibra- tional modes. An alternative pathway from the ground state to the antibonding site exists, which does not go through the bond-center site, but still requires sizable displacements of the Si atoms; this pathway has a slightly higher barrier ~1.9 eV!. The rest of this paper is organized as follows. In Sec. II, we discuss details of the theoretical approach. Our results are reported in Sec. III. In Sec. IV we discuss the implications of these results for device degradation and for experiments per- formed on hydrogen-passivated Si-SiO2 interfaces. Sec. V summarizes the paper.

Structure, energetics, and dissociation of Si-H bonds at dangling bonds in silicon.

We investigate the interaction of hydrogen with dangling bonds in bulk silicon, using first-principles pseudopotential-density-functional calculations. Two geometries are employed: the first is that of a hydrogenated vacancy; the second geometry allows investigation of an isolated dangling bond and minimizes any H-H interactions. The effect of H-H repulsion is quantified. We find that the energy required to remove the hydrogen from the dangling bond and place it in an interstitial position is 2.5 eV. We also investigate the effect of strain in the back bonds on the energy of the Si-H bond. Finally, we propose a low-energy path for the dissociation of the Si-H bond, and discuss the effect of carriers on the dissociation process.