Si Pairs Research Articles

Molecular Dynamics Simulation of Adhesion Effect on Material Removal and Tool Wear in Diamond Grinding of Silicon Wafer

This study aims to clarify the interaction between a silicon wafer and individual diamond abrasives in grinding to support the estimation of optimal grinding conditions for minimizing the subsurface damages and maximizing the removal rate. In this paper, the effects of adhesion (or lubrication) between a Si wafer and a diamond abrasive on the material removal and tool wear were analyzed by means of the molecular dynamics simulation. A few simulations were performed with changing the dissociation (cohesion) energy of a Morse potential function between a pair of Si and C atoms to evaluate the influence of adhesion on the material removal process. As a result, a trend similar to the actual diamond grinding process of silicon wafer was confirmed, which suggested that the reduction in adhesion (or proper lubrication) is effective for the reduction in subsurface damages, grinding forces, grinding temperature and tool wear, but may lead to reduction in the material removal rate as well.

Addition of POSS−T8to the Si(100) Surface

The interaction of the polyhedral oligomeric silsesquioxane (POSS) T8, (HSiO3/2)8 with the Si(100) surface has been studied using a cluster model, represented by the single dimer Si9H12 to represent the surface. Hartree−Fock (HF), density functional theory (DFT), and multi-configuration self-consistent field (MCSCF) wavefunctions have been used to optimize the geometries of stationary points on the potential energy surface. The HF and MCSCF wavefunctions are augmented by second-order perturbation theory for improved relative energies. The POSS reacts with the Si(100) surface saturating dangling bonds on the surface, yielding two possible addition products. One of these forms a Si−Si bond between the POSS and the dimer at the same time that a hydrogen atom is transferred from the POSS to the adjacent silicon atom of the same dimer, with no structural modification of the cage. The other product involves the opening of the POSS cage with the corresponding formation of a pair of Si−Si and Si−O bonds with the ...

Local structure and electronic–spin transition of Fe-bearing MgSiO 3 perovskite under conditions of the Earth's lower mantle

We report first-principles electronic structure calculations on the structural and electronic–spin behaviours of Fe-bearing MgSiO 3 crystals up to the pressure of Earth's mantle. The transition pressure of the Fe-bearing MgSiO 3 from the orthorhombic perovskite (OPv) to the orthorhombic post-perovskite (OPPv) phase decreases with increasing Fe concentration. The lattice distortion has impacts on the electronic–spin behaviour of the Fe ions in the PVs. The spin-polarizations of the Fe ions in the (Fe,Mg)SiO 3 OPvs and OPPvs keep unchanged up to the pressures in the lower mantle. Meanwhile, the Fe-bearing MgSiO 3 OPv containing Fe Mg Fe Si pairs exhibits multiple-magnetic moments co-existing in a large pressure range (from about 78 to 110 GPa), and finally becomes non-magnetic at pressure higher than 110 GPa. These results provide a mechanism to understand the recent experimental results about Fe valence states and the electronic transitions of the Fe-bearing MgSiO 3 under high pressure.

Stability and Dynamics of Frenkel Pairs in Si

Extensive experiments and calculation have shown that interstitials in p-Si diffuse athermally, leading to the conclusion that vacancy-interstitial pairs, or Frenkel pairs (FPs), either rapidly recombine or dissociate, even at cryogenic temperatures. More recent experiments, however, suggest that FPs persist to 150 K. Here we report first-principles calculations of FP properties and resolve the apparent conflict between experiments by showing that athermal interstitial diffusion is suppressed in proximal FPs due to vacancy-interstitial interactions.

First-principles study of iron and iron pairs in Si

Iron is a common transition metal contaminant in Si. The isolated interstitial and several iron–acceptor pairs have been identified by DLTS, EPR, ENDOR and/or other techniques, then studied by theory. Iron also interacts with radiation and implantation damage. Much less is known about these interactions. In this contribution, we present preliminary results of ongoing calculations of interstitial iron, Fe pairs and their interactions with vacancies in Si. The calculations are done in periodic supercells. The electronic states are obtained from spin–density–functional theory with plane wave basis sets. The geometries are optimized using conjugate gradients. The binding energies, charge and spin states are calculated, and the electrically-active gap levels are estimated.

30° Si(g) partial dislocation mobility in nitrogen-doped 4H-SiC

Well-controlled population of dislocations are introduced in 4H-SiC by bending in cantilever mode and annealing between 400 and 700°C. The introduced defects consist of double stacking faults, each bound by a pair of 30° Si(g) partial dislocations, and the expansion of which is asymmetric. The velocity of each individual 30° Si(g) pair is directly measured as a function of stress and temperature on the surface of samples etched after deformation. The activation energies of the 30° Si(g) partial dislocation pairs are strongly stress dependent, ranging between 1.25 and 1.7eV. These values are lower than the ones derived from plasticity experiments. This is probably because 30° Si(g) pairs and double stacking faults are generated in N-doped 4H-SiC (N=2×1018cm−3), with their development being promoted by quantum well action.

Anomalous Hall effect of metallicBe∕Sipairδ-doped GaAs structures

Metallic samples of Be and Si pair $\ensuremath{\delta}$-doped GaAs structures which undergo a metal-insulator transition with a decrease in the hole concentration are investigated by Hall resistance and magnetoresistance measurements. The anomalous Hall effect and negative magnetoresistance are observed from the samples in a temperature range above $70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Magnitudes of negative magnetoresistance and anomalous Hall resistance significantly vary among the samples, although their doping conditions are close to one another. Dependence of anomalous Hall resistance on the temperature and applied magnetic field is closely correlated to that of negative magnetoresistance for each sample. Their dependence is explained on the basis of a paramagnetic state of localized magnetic moments coexisting with itinerant holes in these samples. Both anomalous Hall effect and negative magnetoresistance decrease with lowering the temperature from $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and vanish at a temperature around $70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a possible origin of which is discussed.

Hydrogen-induced crystallization of amorphous silicon thin films. I. Simulation and analysis of film postgrowth treatment with H2 plasmas

We present a detailed atomic-scale analysis of the postdeposition treatment of hydrogenated amorphous silicon (a-Si:H) thin films with H2 plasmas. The exposure of a-Si:H films to H atoms from a H2 plasma was studied through molecular-dynamics (MD) simulations of repeated impingement of H atoms with incident energies ranging from 0.04to5.0eV. Structural and chemical characterizations of the H-exposed a-Si:H films was carried out through a detailed analysis of the evolution of the films’ Si–Si pair correlation function, Si–Si–Si–Si dihedral angle distribution, structural order parameter, Si–H bond length distributions, as well as film surface composition. The structural evolution of the a-Si:H films upon exposure to H atoms showed that the films crystallize to form nanocrystalline silicon at temperatures over the range of 500–773K, i.e., much lower than those required for crystallization due to thermal annealing. The MD simulations revealed that during H exposure of a-Si:H the reactions that occur include surface H adsorption, surface H abstraction, etching of surface silicon hydrides, dangling-bond-mediated dissociation of surface hydrides, surface H sputtering/desorption, diffusion of H into the a-Si:H film, and insertion of H into strained Si–Si bonds.

Selective NMR Measurements of Homonuclear Scalar Couplings in Isotopically Enriched Solids

Scalar (J) couplings in solid-state NMR spectroscopy are sensitive to covalent through-bond interactions that make them informative structural probes for a wide range of complex materials. Until now, however, they have been generally unsuitable for use in isotopically enriched solids, such as proteins or many inorganic solids, because of the complications presented by multiple coupled but nonisolated spins. Such difficulties are overcome by incorporating a z-filter that results in a robust method for measuring pure J-coupling modulations between selected pairs of nuclei in an isotopically enriched spin system. The reliability of the new experimental approach is established by using numerical simulations and tested on fully (13)C-labeled polycrystalline L-alanine. It is furthermore shown to be applicable to partially enriched systems, when used in combination with a selective double-quantum (DQ) filter, as demonstrated for the measurement of (2)J((29)Si-O-(29)Si) couplings in a 50% (29)Si-enriched surfactant-templated layered silicate lacking long-range 3D crystallinity. J-coupling constants are obtained with sufficient accuracy to distinguish between different (29)Si-O-(29)Si pairs, shedding insight on the local structure of the silicate framework. The new experiment is appropriate for fully or partially enriched liquid or solid samples.

Thermal stress analysis for GaInAsP multiple quantum well wafer chemically bonded to Si (100)

An n-InP-based InGaAsP multiple-quantum-well wafer was bonded with p-Si by chemical surface activated bonding at 70°C, and then annealed at 450°C. Different thermal expansion coefficients between InP and Si will induce thermal stresses in the bonded wafer. Planar and cross-sectional distributions of thermal stress in the bonded InP–Si pairs were analyzed by a two-dimensional finite element method. In addition, the normal, peeling, and shear stresses were calculated by an analytic method. Furthermore, x-ray double crystalline diffraction was applied to measure the thermal strain and the strain caused by the mismatching of the crystalline orientation between InP (100) and Si (100). The wavelength redshift of the photoluminescence (PL) spectrum due to thermal strain was investigated via the calculation of the band structure, which is in agreement with the measured PL spectra.

First-principles investigation of a bistable boron-oxygen interstitial pair in Si

Local density functional calculations are used to predict and compare the properties of the two distinct interstitial boron-interstitial oxygen $({\mathrm{B}}_{i}{\mathrm{O}}_{i})$ complexes recently reported in the literature. The electronic and free energies, as well as the small transformation barrier, suggest that both forms of the defect are present at the temperature at which the defect forms. The vibrational spectra of the defects are predicted. The electrical levels of the defect are calculated and compared to experimental data. The existence of two forms of the ${\mathrm{B}}_{i}{\mathrm{O}}_{i}$ defect may have implications for the lifetime degradation of space-based Czochralski-silicon solar cells.

Cycloaddition Reaction of 1,3-Butadiene with a Symmetric Si Adatom Pair on the Si(111)7×7 Surface

We first found experimentally a cycloaddition reaction of a molecule on a symmetry Si pair, 1,3-butadiene on the Si adatom pair of Si(111)7x7, while up to now only asymmetric Si pairs were reported to be involved in cycloaddition reactions on Si surfaces. As the symmetry of a Si pair is expected to influence significantly a cycloaddition product and a reaction pathway, the [4+2]-like cycloaddition product of 1,3-butadiene on the Si adatom pair is suggested to form through a concerted reaction pathway in comparison to a stepwise reaction pathway, which is favorable in the formation of the [4+2]-like cycloaddition product on the asymmetric Si pair (the Si adatom-restatom pair).

Study of the nuclear fusion in a muonic dμ3He complex

An experimental study of the nuclear fusion reaction in the charge-asymmetrical d μ3He complex (d μ3He →α (3.5 MeV) + p (14.64 MeV)) is presented. The 14.64 MeV protons were detected by three pairs of Si(dE-E) telescopes placed around the cryogenic target filled with D2 + 3He gas at 34 K. The 6.85 keV γ rays emitted during the de-excitation of the d μ3He complex were detected by a germanium detector. The measurements were performed at two D2 + 3He target densities, ϕ= 0.0585 and ϕ= 0.168 (relative to liquid hydrogen density) with an atomic concentration of 3He c3He = 0.0496. The values of the effective rate of nuclear fusion in d μ3He were obtained for the first time: $\tilde{\lambda}_{f} = (4.5^{+2.6}_{-2.0}) \times 10^5 ~ \mbox{s}^{-1} (\varphi = 0.0585)$ ; $\tilde{\lambda}_{f} = (6.9^{+3.6}_{-3.0}) \times 10^5 ~ (\varphi = 0.168)$ . The J=0 nuclear fusion rate in d μ3He was derived: $\lambda^{J=0}_{f} = (9.7^{+5.7}_{-2.6}) \times 10^5 ~ \mbox{s}^{-1} (\varphi = 0.0585)$ ; $ \lambda^{J=0}_{f}=(12.4^{+6.5}_{-5.4}) \times 10^5 ~ \mbox{s}^{-1} (\varphi = 0.168)$ .

Electron spin resonance of platinum pair complex in silicon

We investigated a Pt–Pt pair in Si by electron spin resonance (ESR) measurement. Two kinds of ESR spectra from Pt–Pt pairs which had been already reported were not detected. However, we observed other ESR spectrum of Pt–Pt pair. The ESR spectrum showed the hyperfine structure corresponding to two equivalent Pt atoms. The anisotropic g-tensor obtained by analyzing the angular dependence of the ESR signals indicated the orthorhombic ( C 2 v ) symmetry with the g-values of g x = 2.1 1 , g y = 2.3 1 , g z = 2.0 9 . The g z axis was along [0 0 1] direction. The g y and g z axes were along [1 1 0] and [ 1 ¯ 1 0 ] directions, respectively. The ESR spectrum of Pt–Pt pair was observed in the sample only under illumination. This suggests that a change in the charge state of Pt–Pt pair is caused by carrier excitation.

Study of Pathway of Hydrogen Migration and Desorption on SiGe(100) Surface Using Ab Initio Calculations

Ab initio calculations have been carried out to investigate the pathways of H-atom migration and H2 desorption on a mixed SiGe(100)-2×1 surface using the cluster model. The H2 recombinative desorption is the rate-determining step in hydrogen migration and desorption on SiGe(100) surfaces, since the energy barrier to H-atom migration is generally lower than that of H2 desorption. The energy barriers for H2 desorption from the interdimer, the Si–Ge pair, (52.8 kcal/mol), and the Ge–Ge pair, (45.1 kcal/mol), are lower than that for the Si–Si pair by 7.5 and 15.2 kcal/mol, respectively. Thus, the SiGe(100)-2×1 surface in chemical vapor deposition provides more dangling bonds than the Si(100)-2×1 surface because of Ge inclusion. In contrast, the chemisorbed H tends to stay on the Si-site, since the barrier for H-migration from the Ge-site to the Si-site is lower that in the opposite direction by 5.6 kcal/mol. Hence, a considerably higher percentage of Ge sites are dangling bonds, compared with Si sites on the SiGe(100) surface. Related transition state structures in the migration and desorption steps are also discussed.

Cu0*: A metastable configuration of the{Cus,Cui}pair in Si

First-principles theory shows that the substitutional-interstitial copper pair in Si (Si-${\mathrm{Cu}}_{s}\ensuremath{\cdots}{\mathrm{Cu}}_{i}$) has a metastable state with ${\mathrm{Cu}}_{i}$ very near a tetrahedral interstitial site in a trigonal ${\mathrm{Cu}}_{s}\text{\ensuremath{-}}\mathrm{Si}\ensuremath{\cdots}{\mathrm{Cu}}_{i}$ configuration that exhibits three low-frequency pseudolocal vibrational modes. The lowest of them, at $40\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, has ${A}_{1}$ symmetry and is the likely source of the phonon sidebands observed at $52\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ in the photoluminescence band of a defect known as $^{*}\mathrm{Cu}_{0}$.

Hydrogenation∕deuteration of the Si–SiO2 interface: Atomic-scale mechanisms and limitations

The mechanisms responsible for exchange of hydrogen with deuterium at the Si–SiO2 interfaces are analyzed through first-principles calculations. The associated reaction barrier is found to be 1.94 eV, in agreement with experiments of Cheng et al. [IEEE Electron. Device Lett. 22, 203 (2001); Cheng et al.J. Appl. Phys. 90, 6536 (2001)] that studied the kinetics of the phenomenon through electrical measurements. The substitution of hydrogen by deuterium can be limited by another possible process, the breakup of the D2 molecule to a pair of Si–D bonds, which has a similar barrier.

Lateral Growth and Generation of the Pb0 Center in the Initial Oxidation on the Si(100) Surface

Various kinds of oxygen-adsorbed configurations with oxygen coverages of up to two monolayers (ML) were studied through first-principles calculations to elucidate mechanisms of the layer-by-layer growth and of interfacial defect generation in initial oxidation processes. It was found that oxidation proceeds almost laterally. When the coverage reaches to around 1 ML, first-layer oxidation temporary saturates once, although there still remains oxidation sites in the first-layer. Partial second-layer oxidation opens again a channel of the first-layer oxidation. When the coverage exceeds 1.25 ML, oxygen atoms can be incorporated into a bridging site in the second layer, generating twofold-coordinated Si atoms in the third layer. Emission of such twofold-coordinated Si atoms leaves weakly bonded Si pairs in the fourth layer. When such pairs happen to be generated close to each other, they transform into a chain of Si trimers with one Pb0 center at each end. Pb0 centers appear initially in the fourth layer.

Investigation of nodule growth in ion beam sputtered Mo∕Si multilayers

In this study, the nodule growth in ion beam sputtering Mo∕Si coatings used for extreme-ultraviolet (EUV) lithography masks has been studied in relation with the number of Mo∕Si pairs (period 7 nm). To trigger this growth, initial particles of different sizes (d=40–155nm) were used. With a deposition angle of 30° and after the deposition of 40–60 Mo∕Si pairs, the lateral size of nodules was found to grow up to ∼2d while its height ranged from d∕6 to d∕2 depending on the initial particle diameter. This lateral growth was demonstrated to mainly result from shadowing effect. Besides, a vertical smoothing effect was evidenced even in the case of relatively large initial seed particles (70–155 nm). It is attributed to adatom surface diffusion which is also thought to promote a slowdown in the nodule lateral growth when increasing the coating thickness. Finally, a real case of mask blank realization is presented showing that a good knowledge of nodule growth is essential to properly analyze the defect characteristics of EUV mask blanks.

Full-band Monte Carlo simulations of photo excitation in silicon diode structures

In this study, a full-band particle-based simulator is used to model photo-generated electron–hole pairs in Si to investigate ultra-fast charge transport. This work is motivated by previous simulations of transient transport in III–V material as well as recent experimental measurements of optically excited Si pin diodes. The simulation results show evidence of velocity overshoot at high fields (greater than 100 kV cm−1), and can be attributed to momentum relaxation.