Kazutami Tago

Molecular structures, binding energies and electronic properties of dopyballs C59X (X=B, N and S)

Abstract When optimized by a molecular orbital method with Harris functional and spin-restricted approximations, the molecular structures of C 59 B and C 59 N are found to be almost the same as that of C 60 , while that of C 59 S is different from that of C 60 . The binding energies calculated self-consistently are 6.05 (C 60 ), 6.03 (C 59 B), 6.00 (C 59 N) and 5.91 (C 59 S) eV/atom. The energy gaps between the LUMO and the HOMO or the half-occupied molecular orbital are 1.50 (C 60 ), 1.06 (C 59 B), 0.30 (C 59 N) and 0.63 eV (C 59 S), and the Mulliken charges of the doped B, N and S atoms are 4.5, 7.2 and 15.5, respectively, meaning the N atom exists as an acceptor, while the B and S atoms exist as donors in these dopyballs.

Analysis of Plasma Chemical Reactions in Dry Etching of Silicon Dioxide

A computational model for chemical reactions in plasmas has been developed and applied to the gas-phase chemistry of dry etching of silicon dioxide. An ab-initio molecular orbital method is used to determine the dissociation processes and the threshold energies for gases and neutral radicals. Plasma chemistry is calculated by the plasma chemical kinetic method. The chemical compositions of the dry etching plasmas were investigated for fluorocarbon gases. Calculated ion fluxes, electron temperatures, and densities agreed with experimental results within factors of three. The differences in plasma characteristics between CHF3/CH2F2 and C4F8 were attributed to differences in the products and threshold energies of the dissociation reactions. Correlations could be found between the composition of radicals in a plasma and the etch selectivity in C4F8.

Radical and Ion Compositions of BCl3/Cl2 Plasma and Their Relation to Aluminum Etch Characteristics

Plasma compositions in BCl3/Cl2 were calculated using a molecular orbital method and a plasma kinetic method. The key factors for plasma compositions and their relations to the etch characteristics of Al-based multilayers were investigated. The etch rate of Al seemed to be correlated with the Cl density rather than the Cl2 density. The etch rates of TiN and the resist were also related to the Cl density and the ion density. Therefore the ion energy distribution (IED) impinging on the wafer was also calculated and the rf frequency dependence of the selectivity of the TiN/resist was evaluated using an etching model. Even if the rf frequency increased to 10 MHz, where the IED had a single peak, the predicted selectivity was slightly improved. A narrower IED was required.

Model prediction of radical composition in plasmas and correlation with measured etch characteristics of silicon dioxide

A computational model for plasma chemical reactions has been developed. An ab initio molecular orbital method was used to determine dissociation paths and their threshold energies. Plasma characteristics were calculated by a plasma kinetic method. The radical compositions in , with additional gases such as Ar, He and , were calculated. Radicals influencing the selective etching of over were analysed. With increased microwave power or decreased flow rate, density decreased and CF, C and F densities increased. The increase of radicals with abundant carbon relative to fluorine would result in high etch selectivity of over and a low etch rate. Increases in the concentration of F radicals are correlated with increases in etch rates. Electron temperature was high with He addition, and dropped with alone and Ar addition discharges. On the contrary, the electron density was high in the reverse order. The highest etch selectivity was obtained with He addition. A high electron temperature discharge would be one solution to obtain high etch selectivity of over .

Non-local density functional calculations of binding energies of carbon fullerenes Cn, with n = 10, 12, 16, 20, 24, 28, 32, 36, 50, 60, 70, 80, 90, 100, 110 and 120

Abstract Using a molecular orbital method based on the non-local density functional formalism, we have calculated the binding energies and HOMO—LUMO gaps of carbon fullerenes C n assuming that all bond lengths in each fullerene are the same. The results are as follows: (1) The fullerenes containing quadrilateral rings are less stable than those with only pentagonal and hexagonal rings. (2) With a larger number of hexagonal rings in a fullerene, the binding energy is larger. (3) C 60 , C 70 , C 100 , C 90 and C 32 have especially large HOMO—LUMO gaps and are expected to be less reactive.

Bonding and Electronic Properties of Substituted Fullerenes C58B2, C58N2 and C58BN

Abstract When optimized by a molecular orbital (MO) method with Harris approximation, structures of substituted fullerenes C58B2, C58N2 and C58BN are almost the same as that of 0, and the self-consistently calculated binding energies of C58B2 and C58BN are similar to that of C60, while that of C58N2 is much smaller. The energy gaps between the highest-occupied MO and the lowest-unoccupied MO depend on the positions of substituted atoms, being 0.49-0.54 (C58B2), 0.23-0.28 (C58N2) and 0.10-0.86 eV (C58BN).

A plasma kinetics model: analysis of wall loss reactions in dry etching of silicon dioxide

Abstract Computational models for gas-phase chemical reactions in plasmas and for sticking reactions on metallic Al walls have been developed and applied to the plasma chemistry of dry etching of silicon dioxide. Dissociation paths and threshold energies of gases are determined by using an ab initio density functional molecular orbital method, and dissociation cross sections are approximated. The electron energy distribution function is determined by using a particle-in-cell model with the Monte Carlo collision method, and dissociation reaction rates are determined. Plasma densities, electron temperatures. and radical densities are calculated by a kinetic model which consists of the fluid equations for plasmas and rate equations for radicals. The model effectiveness was confirmed by results comparison for the Ar discharge in an radio-frequency device. The chemical compositions of the dry etching plasmas have been investigated for C 4 F 8 . Calculated electron temperatures and densities agree with experimental results within factors of three. Correlations could be found between the composition of radicals in the plasma and the etch selectivities in C 4 F 8 . Adsorption potentials of fluorocarbon radicals on Al (III) surface clusters have been calculated by using molecular orbital method, and sticking coefficients are estimated. Sticking coefficient of fluorine atom is the largest and decrease in order of F, C, CF, H, CF 2 , and CF 3 . Effects of hypervalence bonding at Al surface are discussed. Phenomena [1] of no film depositions in CF 4 RF plasma and film depositions in RF plasma of CF 4 mixed with H 2 were explained by hypervalence reactions of Al.

Investigation into standard parameters of motor drive systems

This paper provides a standard motor model, parameters, and a design of controllers for simulation of motor drive systems. In the motor drives working group of Investigating R&D Committee on applied simulation for power electronics systems in IEEJ, standard models for simulation of motor drive systems have been discussed. Parameters of more than 330 motors have been gathered from among released data sheets and specifications from manufacturers, IEEE transactions, IEEJ papers, and JIPE papers. Tendency of the parameters have been also investigated. A simulation example based on the investigation of dc motors is shown and the validity is demonstrated.

A Molecular Orbital Calculation Method Considering Crystal Fields

An evaluation method for crystal fields in the Discrete Variational (DV)-Xα molecular orbital calculation is presented. Its main features are as follows. First, molecular orbitals for a cluster are calculated. Then the electrostatic potential of a unit cell is added to the hamiltonian of the cluster. This electrostatic potential is obtained by using the Coulomb potential of the electron density. The electron density is estimated by the square of the molecular orbitals of the cluster so that the potential of the unit cell is consistent with that of the cluster. Finally the potential of the unit cell is summed over the infinite crystal by using the Ewald sum method. The approach is applied to the MgO crystal.

Vectorized Calculations and Use of Fast Semiconductor Memories in the Dv-Xα Method

Two types of vectorized programs of the discrete varia tional Xα method with the basis set of Slater-type or bitals have been developed. The first type calculates a basis function every time that it is used and the second type reads a basis function from outside memories. They are examined for the most efficient way of per forming calculations with the HITAC S-810/20 supercom puter (630 MFLOPS at peak) and its available outside memory devices. The acceleration factor of computation by the first type of program over scalar processing is more than 12. The second type of program has no ad vantage over the first in small electron systems of atomic clusters with primitive basis functions. But in larger systems such as Si2O7H6 with complex basis functions, the second type of program, used with semi conductor memories, results in 11 times less CPU time than the first type of program.