To understand surface segregation behaviour of B, Ga, As, and Sb dopant atoms on Ge (100) and Ge (111) surfaces, the potential energies of these dopant atoms in the five top layers of the surfaces were evaluated by first-principles molecular orbital calculations of model clusters. The obtained potential energy curves of these dopant atoms for Ge (100) closely resemble those for Si (100) surface. On the other hand, Ge (111) surface exhibits different potential profiles as compared with Ge (100) surface. The thermal activation energy between the adsorbed state and sub-surface state was also evaluated for each dopant atom. These energy data determining the driving force and dynamical property of dopant segregation help us to understand the difference in dopant surface segregation phenomena on Ge(100) and Ge(111) surfaces from an atomistic point of view.

The SAC (symmetry-adapted-cluster) and SAC-CI theories based on the cluster expansion of the wavefunction have been applied to the calculations of the potential energy curves of the ground, excited...

Metal nanoparticles need coating material so as to avoid aggregating to each other. On the contrary, there are occasions when the coating materials are required to be removed. Here, a theoretical model to relate removability of coating materials to their molecular structure is suggested. The model is used to find an optimum coating material, secondary amine, for use in low-temperature interconnection material. An interconnection made of methyloctylamine-coated silver nanoparticles was formed between a pair of copper electrodes by heating and pressurizing the nanoparticles and electrodes at 250 °C and 2.5 MPa, respectively, for 150 s. Shear strength and thermal conductivity of the formed interconnection were 17.8 MPa and 219 W/mK, respectively. This thermal conductivity value is greater than that obtained using Pb–Sn and silver solders.

Soft x-ray-excited angle-resolved photoemission results for nitride films formed using nitrogen–hydrogen radicals on Si(100), Si(111), and Si(110) are reported. The data were obtained using synchrotron radiation, which allowed the Si 2p, N 1s, and O 1s levels to be investigated with the same probing depth. The following main results were obtained: (1) the Si3N4 film is covered with one monolayer of Si–(OH)3N. Its areal density is 15% smaller on Si(111) than on Si(100) and Si (110), (2) the Si3N4/Si interfaces on all three surfaces are compositionally abrupt. This conclusion is based on the observation that no Si atoms bonded with three N atoms and one Si atom were detected, and (3) the observation that the number of Si–H bonds at the Si3N4/Si(110) interface is 38%–53% larger than those at the Si3N4/Si(100) and Si3N4/Si(111) interfaces indicates a dependence of the interface structure on the orientation of the substrate.

To clarify the microscopic mechanism of Negative-Bias Temperature Instability (NBTI), which is one of serious reliability issues in CMOS technology, the transfer reaction of the positive fixed charge at the Si/SiO2 interface accompanied by hydrogen migration was investigated using the ab initio molecular orbital method. Comparing the activation energies, we determined the most likely reaction path. We found that the reaction path can be stabilized more by migration of an electrically neutral H atom from a Si substrate to a positively charged O atom than by migration of a proton from a Si substrate to an electrically neutral O atom. The calculated Mulliken atomic charges and atomic spin densities also supported our conclusion.

Utilizing the structure of porous SiOC determined in our previous study, we investigated a mechanism for improving the properties of porous SiOC film by ultraviolet irradiation (UV curing). The generation of a Si-O-Si cross link from an OH group and its adjacent CH3 group is the primary process in UV curing. This cross-link generation enhances mechanical strength of the material and lowers the dielectric constant. Decrease in the number of CH3 groups and increase in the number of Si-H bonds, both due to UV curing, cause slight increases in mass density and dielectric constant of the film.

The transfer reaction of the positive fixed charge at the Si/SiO2 interface accompanied by hydrogen migration, which is a basic phenomenon to consider negative-bias temperature instability, was investigated using the ab initio molecular orbital method. Comparing the activation energies, we determined the most likely reaction path. We found that the reaction path can be stabilized more by migration of an electrically neutral H atom from a Si substrate to a positively charged O atom than by migration of a proton from a Si substrate to an electrically neutral O atom. The calculated atomic charges and atomic spin densities also supported our conclusion.

On the basis of electron spin resonance (ESR) measurements, we observed a unique paramagnetic center (Tb center, g=2.003) in porous low-dielectric-constant (low-k) carbon-doped silicon oxide (SiOCH) film after annealing the film in vacuum. Fourier transform infrared spectroscopy (FT-IR) spectra indicated that the number of Si–CH3 bonds in the SiOCH film decreased with increased Tb-center absorbance. Molecular calculations indicate that this paramagnetic center differs from an E' center and has a microstructure with carbon atoms in its backbond. A Tb center was also observed after annealing using ultraviolet (UV) light or an electron beam (EB), which both increase film leakage current.

The authors measured soft x-ray-excited angle-resolved photoemission from Si 2p, N 1s, and O 1s core levels, and valence band for nitride films formed on Si(100), Si(111), and Si(110) using nitrogen-hydrogen radicals with the same probing depth. The Si3N4∕Si interfaces formed exhibited an almost abrupt compositional transition. Furthermore, the crystal orientation of Si substrate affects the total areal density of subnitrides but not the valence band offset at the Si3N4∕Si interface.

We determined the most probable atomistic structure of a porous carbon-doped oxide (k=2.55) by computer simulations. Utilizing the determined structure, investigation of the mechanism of UV cure was performed. Replacement of CH3 groups by H atoms during LTV cure increases mass density and dielectric constant, while generation of a Si-O-Si bond from CH3 and OH groups causes characteristic change in IR spectrum, increases in mass density and Young's modulus, and decrease in dielectric constant. The balance between the two chemical reactions determines the properties of the material after UV cure.

We determined the most probable atomistic structure of an ultra-low-k material (k≅ 2.5) by computer simulations. Among the candidate structures generated by a molecular-dynamics calculation, the most probable one that reproduces the observed properties was selected using a first-principles density-functional-theory calculation. The candidate structures consisted of Si-O-Si network with some silicon atoms, each of which had a CH 3 group or a hydrogen atom bonded. The structure with CH 3 groups but no hydrogen atom reproduced the experimental properties best. This structure was then used to investigate the behaviors of the material irradiated with ultraviolet light.

The mechanism of UV and EB cure processes for porous low-k SiCOH materials was investigated by using experimental results obtained using PECVD and SOD films as well as simulated results. Both UV and EB cures induced dielectric constant change and Young's modulus improvement because Si-OH elimination (moisture removal) and cross-link formation occurred during film shrinkage. Excess UV curing, however, caused defects in the porous SiCOH film, as indicated by ESR analysis. The mechanism discussed in this work is applicable to most UV/EB cure systems and PECVD/SOD SiCOH materials for 45-nm-node Cu interconnects.

To investigate the origin of the electric-field dependence of negative-bias temperature instability (NBTI), we calculated the change in the activation energies of the dissociation reaction of a Si–H bond caused by an electric field. The calculated activation energies show that the change is too small to explain previously reported experimental electric-field dependence. On the other hand, a hole generated by the electric field in the silicon/gate-dielectric interface reduces the activation energy much more. We propose a NBTI mechanism based on the calculated activation energies. This mechanism can be applied to estimate NBTI lifetime over a wide range of electric fields.

Degradation process of a metal–oxide–semiconductor (MOS) structure with NO-nitrided SiO2 under negative-bias-temperature (NBT) and Fowler–Nordheim (FN) stresses has been investigated. The FN stress immunity improves with increasing nitrogen concentration at the SiO2/Si interface, while the incorporation of excess nitrogen (more than 3 at. %) at the SiO2/Si interface accelerates NBT instability (NBTI). This stronger immunity of NO-nitrided SiO2 under FN stress is due to the stronger Si–N bonds formed by NO nitridation at the interface. Without hydrogen annealing to form Si–H bonds, the MOS capacitors do not show NBTI. This indicates that the Si–N bonds are not broken under NBT stress and the main cause of the NBTI is the breaking of the Si–H bonds. The NO nitridation decreases the number of Si–H bonds and thus suppresses NBTI. However, nitrogen provides hole-trap centers. Hydrogen at the interface is dissociated and bonds to the hole-trapping nitrogen, so interface traps are left behind. An excess amount of nitrogen thus accelerates NBTI.

The interfacial structure of nitrous-oxide- (NO-)nitrided SiO2/Si is determined on the basis of the configuration of the P-b centers and the results of physical analysis. We used electron spin-resonance analysis to observe a decrease in the number of P-b centers after NO annealing, which corresponds to the decrease in the density of interface traps. The nitrogen bonds at the interface were analyzed by x-ray photoelectron spectroscopy. An asymmetric N 1s peak at around 398 eV was detected; the peak may be decomposed into two peaks with a binding-energy difference of 0.6 eV. This core-level shift originates in the difference between the numbers of oxygen atoms that are second-nearest neighbors of the nitrogen which terminates the P-b0 and P-b1 centers. (C) 2002 American Institute of Physics.