Yu. N. Morokov

Excess silicon at the silicon nitride/thermal oxide interface in oxide–nitride–oxide structures

The chemical composition and structure of Si3N4/thermal (native and wet) SiO2 interface in oxide–nitride–oxide structures are studied by using secondary ion mass spectroscopy, electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES) measurements. EELS and AES experiments show the existence of excess silicon at the Si3N4/thermal SiO2 interface. Excess silicon (Si–Si bonds) at Si3N4/SiO2 interface exists in the form of Si-rich silicon oxynitride. Numerical simulation of the Si–Si bond’s electronic structure by using semiempirical quantum-chemical method (MINDO/3) shows that Si–Si defects act as either electron or hole traps. This result explains the abnormally large electron and hole capturing at this interface reported earlier.

Structure of small hydrogenated silicon clusters: global search of low-energy states

Abstract Quantum-chemical calculations of the Si n H m clusters structure are carried out for n =6–16 and wide range of hydrogen content. The low-energy states are found using a procedure which allows to construct a wide row of qualitatively different structures and reveals a number of local minima for each structural type. General structural peculiarities of Si n H m , which appear for the clusters containing more than 12 silicon atoms, are discussed.

Electronic structure of amorphous Si3N4 : experiment and numerical simulation

Abstract The electronic structure of amorphous silicon nitride was studied by XPS, X-ray emission, and ELS. The partial densities of states for silicon (3s, 3p, 3d) and nitrogen (2s, 2p) atoms were determined. The results of experiments were compared with the calculated electronic structure of Si 3 N 4 . The calculations were made using quantum-chemical semiempirical method MINDO/3 in cluster approximation. The top of the Si 3 N 4 valence band in terms of band structure is two-degenerated. There are Si3s,3p-N2s,2p bonding states and N2p π nonbonding states at the top of valence band. The electronic structures of Si 3 N 4 and SiO 2 are similar. The experimentally energy of plasmon oscillations determined for Si 3 N 4 is 23.5 eV. It was found that not only Si3s,3p, N2p orbitals of upper valence band take part into plasmon oscillations but N2s states of lower valence band, too.

Numerical simulation of intrinsic defects in SiO2 and Si3N4

The electronic structure of major intrinsic defects in SiO2 and Si3N4 was calculated by the MINDO/3 and the density-functional methods. The defects that are of interest from the standpoint of their ability to capture electrons or holes were considered; these centers include the three-and two-coordinated silicon atoms, the one-coordinated oxygen atom, and the two-coordinated nitrogen atom. The gain in energy as a result of capturing an electron or a hole with allowance made for electronic and atomic relaxation was determined for these defects. The experimental X-ray spectra for both materials are compared with calculated spectra.

Two-fold coordinated nitrogen atom: an electron trap in MOS devices with silicon oxynitride as the gate dielectric

Abstract Having conducted semiempirical quantum-chemical simulation (MINDO/3) of several clusters at different charge states, we identify that the two-fold coordinated nitrogen atom with an un-paired electron (Si2N·) is the most responsible trap center for the observation of large electronic capturing in SiOxNy. Our calculations also show that electron localized in this defect will result in spin dissipation. Trap formation and removal mechanisms during nitridation and re-oxidation are also discussed in this work.

Simulation of electronic structure of Si-Si bond traps in oxide/nitride/oxide structure

Abstract Numerical simulation using MINDO/3 was performed to study the electronic structure of Si–Si bond traps in the silicon oxide/nitride/oxide structure. Results show that the neutral diamagnetic Si–Si bond in Si3N4 can capture both electrons and holes. Simulation results also suggest that the creation of charged diamagnetic defect pairs is unfavorable in Si3N4. Electron and hole trapping models are also proposed for the Si–Si bond.

Characterization of the silicon nitride-thermal oxide interface in oxide-nitride-oxide structures by ELS, XPS, ellipsometry, and numerical simulation

Abstract This work studies the properties of the SiO 2 –Si 3 N 4 interface in oxide–nitride–oxide (ONO) structures by using energy loss spectroscopy, X-ray photoelectron spectroscopy, ellipsometry measurements and numerical simulation. By oxidation the as-deposited Si 3 N 4 , silicon–silicon bonds at Si 3 N 4 –thermal SiO 2 interface are found. These excess Si–Si bonds are produced by replacing nitrogen with oxygen during the oxidation of Si 3 N 4 . We further propose that the Si–Si bonds are the major trap center at the Si 3 N 4 –SiO 2 interface. With MINDO/3 numerical simulation, we have found that the Si–Si bonds can capture both electrons and holes at the top Si 3 N 4 –SiO 2 interface. These bonds are proposed to be the responsible candidate for the positive charge accumulation in re-oxidized nitrided oxide.

MINDO/3 calculation of the electronic structure of silicon nitride

The electronic structure of silicon nitride has been calculated by the semiempirical quantumchemical method MINDO/3 in the cluster approximation. The effect of cluster size and of boundary conditions on the partial density of one-electron states is analyzed. The results of the calculation are compared with experimental data on amorphous silicon nitride. The origin of a peak in the upper part of the valence band, which is seen in the SiL2,3 spectrum but not reproduced in the calculations is discussed.

An elliptic method for construction of adaptive spatial grids

Abstract This paper contains some new results concerning the development of a universal method for the construction of spatial grids. The method is based on numerical solution (a stabilizing correction scheme) of inverted one-, two-, and three-dimensional Beltrami equations and diffusion equations with respect to the control metric. One- and two-dimensional equations are used for the generation of grids on the edges and faces of a domain. Using three-dimensional equations, a grid is constructed inside a domain. Examples of model adaptive spatial hexahedral and prismatic grids and a grid for the calculation of the propagation of a passive impurity in the atmosphere are demonstrated.

Structure of hydrogenated silicon clusters. Small clusters

The ground state structures of silicon hydride clusters SinHm containing up to 12 silicon atoms are obtained by numerical modeling. The cluster geometry is optimized for a wide set of initial structures using the MINDO/3 approximation for Monte Carlo simulation of interatomic interactions. The energy of the cluster depending on the content of hydrogen is studied, and it is shown that the Si-H and Si-Si bond energies depend little on the cluster size.