Vladimir Zubkov

Modeling Copper Diffusion in Silicon Oxide, Nitride, and Carbide

Density functional theory was applied to simulate copper diffusion in silicon oxide, nitride, and carbide (SiO x , SiN x , SiC x ). Because copper drift into oxide is significantly enhanced by negative bias, copper ions are the active diffusing species. Clusters and, in some cases supercells, modeling various ring configurations of the amorphous networks of silicon oxide, nitride, and carbide were employed. Interactions of both neutral copper and its cation, Cu + , with the network were explored. Calculations revealed a strong binding of Cu + to SiO x , SiC x , and SiN x in contrast with neutral Cu. The Cu+ attraction to carbide clusters is significantly lower than to SiO x and SiN x , explaining the effective barrier properties of SiC x . The estimated lower bounds for activation energies for Cu + hops between stable ring clusters of SiO x and SiN x are similar. This implies that the difference in Cu diffusion properties between oxides and nitrides is likely due to a higher percentage of large rings in amorphous oxides compared with nitrides. An approach to increasing the resistance of oxides to Cu + diffusion is suggested.

Integrated simulation of the plasma-assisted gate oxide nitridation

Quantum chemical calculations were employed to get insight into the mechanisms involved in plasma-induced nitridation of gate oxide that will suppress boron penetration. The roles played by the nitrogen cations and atoms were explored. It was shown that B interaction with siloxane rings that contain incorporated nitrogen yielded a larger energy gain than rings without nitrogen. This explains the chemical nature of the nitrogen-induced barrier effect. Monte Carlo simulations were used to simulate the necessary energy of incident N2 cations to produce the bond cleavage down to a particular depth in the amorphous SiO2 layer. A combination of the HPEM and PCMC codes were used to simulate nitrogen atomic and cation fluxes and their energy distributions at the wafer surface. Combining simulated cation fluxes and their energy distributions at the wafer surface. Combining simulated cation energies with PROMIS Monte Carlo simulation results make it possible to derive the plasma process parameters that will permit a desired level of nitridation to be reached.

Plasma-induced nitridation of gate oxide dielectrics: Linked equipment-feature atomic scale simulations

Quantum chemical calculations were employed to get insight into the mechanisms involved in plasma-induced nitridation of gate oxide that will suppress boron penetration. The roles played by the nitrogen cations and atoms were explored. It was shown that B interaction with siloxane rings that contain incorporated nitrogen yielded a larger energy gain than rings without nitrogen. This explains the chemical nature of the nitrogen-induced barrier effect. Monte Carlo simulations were used to simulate the necessary energy of incident N2 cations to produce the bond cleavage down to a particular depth in the amorphous SiO2 layer. A combination of the hybrid plasma equipment model and plasma chemistry Monte Carlo codes was used to simulate nitrogen atomic and cation fluxes and their angular and energy distributions at the water surface. Combining simulated cation energies with PROMIS Monte Carlo simulation results makes it possible to derive plasma process parameters that will permit a desired level of nitridation...

Bandgaps of zigzag finite-length nanotubes ab initio calculations: ground state degeneracy and single-electron spectra

Different versions of ab initio quantum chemical models (cluster and periodic boundary conditions approximations) have been used to analyze the effect of finite length and the partial filling of the highest occupied orbital on the band-gaps of carbon nanotubes. In agreement with the previous calculations in the tight-binding approximation and pi-electron open shell model, it has been shown that the ground state of the nanotube with the zigzag structure is triplet. It has been confirmed that these tubes exhibit metallic or semiconductor properties with a very narrow half-filled conduction band. The band-gap is of order few tens of eV, and it is estimated that approximately 0.1-0.2% of pi-electrons belong to the conduction band of finite zigzag nanotubes. The triplet state is predicted to be the ground state of finite-length carbon nanotubes.