Koji Satake

Experimental and numerical studies on voltage distribution in capacitively coupled very high-frequency plasmas

A non-uniform voltage distribution across a driven electrode results in inhomogeneous film deposition in large-area, very high-frequency (VHF) plasma reactors. Here we perform experimental and numerical studies on the voltage distribution across the electrode. Two kinds of dedicated vacuum chambers are prepared for one- and two-dimensional observations of the voltage and the plasma distributions. A comparison between the measured voltage and the plasma distribution clearly shows a good agreement between the two. In principle the plasma distribution is governed by the standing wave of the voltage on the driven electrode for an at least one-dimensional electrode. A numerical model based on transmission-line modelling is presented for calculating the voltage distribution. The influence of plasma conditions such as the electron density and the sheath length included in the model on the voltage distribution is investigated through comparison of the model predictions with the experimental results. The correlation between the plasma conditions and the propagation constant of the model suggests that the sheath length dominates the wavelength; in contrast, the electron density dominates the decay of the wave propagation. Using the parameters of the plasma conditions estimated from the experimental results, the model can predict the voltage distribution across a ladder electrode of size 45 cm × 55 cm in a large-area VHF plasma reactor.

Molecular dynamics simulation of ion bombardment on hydrogen terminated Si(001)2×1 surface

Molecular dynamics simulations were performed to investigate H2+ and SiH3+ ion bombardment of hydrogen terminated Si(001)2×1 surfaces. Normal incidence ion bombardment effects on dangling bond generation, adatom diffusion, and nucleation were studied as a function of incident energy between 10 and 40 eV. The dangling bond generation rate due to H2+ impacts at 20 and 40 eV was about twice that of SiH3+. However these effects appeared to be insignificant compared to probable neutral radical effects under typical plasma-enhanced chemical vapor deposition conditions. The enhanced diffusion of Si adatoms due to ion bombardment was observed to be minor in comparison with thermal diffusion and the disruption of ledge sites due to SiH3+ ion bombardment is not significant, with ion incident energies up to 40 eV. Ion bombardment in the incident energy range between 10 and 20 eV can contribute the modification of surface kinetics without bulk damage.

A technique for uniform generation of very-high-frequency plasma suited to large-area thin-film deposition

Two very-high-frequency powers between which the phase difference is varying in split of time are supplied to a ladder-shaped electrode through multiple feeding points located at symmetrical positions of the electrode to generate a large-area uniform plasma. Theoretical calculations of the voltage distribution at several phase difference show good agreement with experiments. Plasma emission uniformity within ±15% is demonstrated at 60MHz for the substrate size of 1.4×1.1m, with nitrogen gas of 10Pa.

Silicon epitaxial growth on the Si(001)2×1 surface from silane using dynamic Monte Carlo simulations

Dynamic Monte Carlo (DMC) simulations are carried out on silicon (001)2×1 surface under 100% silane gas chemical vapor deposition condition as a function of surface temperature (600–800° C) and pressure (6 and 12 mTorr). The reactant on the surface from gas-phase is assumed to be the silane molecule. The rates and probabilities of surface reactions are determined a priori by recent ab initio calculation results in the literature. The DMC method can reveal not only the short-time microscopic mechanism but also predict the macroscopic phenomena such as deposition. The calculated growth rate and Arrhenius activation energy of growth depending on temperature show good agreement with experimental results. The results suggest that the low activation energy regime above 700 °C is associated with a process controlled by silane dissociative adsorption. In contrast, the higher activation energy regime below 700 °C is supposed to be governed by hydrogen desorption. The periodic change of surface structure that is si...

Modeling of microcrystalline silicon film deposition in a capacitively coupled radio-frequency plasma reactor

We present a numerical model of plasma-enhanced chemical-vapor deposition of hydrogenated microcrystalline silicon (μc-Si:H) film from SiH4 and H2 gas mixtures in a capacitively coupled radio-frequency plasma reactor. The model takes into account electron-impact, gas-phase, and surface reactions within a well-mixed reactor model. Plasma parameters such as the electron density, the electron temperature, and the electron-impact reaction rates are determined through a discharge model and used as inputs for the reactor model. The gas-phase reactions include electron-impact and neutral–neutral reactions. Some of the surface reaction rates are determined using quantum chemical calculations and transition state theory. In the reactor model, concentrations of each chemical species are calculated at steady state using mass conservation equation uniformed throughout the reactor. Numerical results of the deposition rate as a function of the plasma reactor operating parameters show good agreement with experiments. Ba...

Behavior of negative ions and aggregation process of particle growth in silane plasma

Particle formation processes in silane plasma have been studied by means of ab initio molecular orbital method and the Derjaguin–Landau–Verway–Overbeek (DLVO) theory. The results from a quantitative comparison between the Si–H bonding energy of negative species and that of neutral ones suggested the presence of the polymerization pathways via negative species. The DLVO theory has been applied to calculate the interaction potential energy between the charged particles. It was found that the heterogeneous aggregation accelerates the particle growth.

Numerical modeling of silicon film deposition in very-high-frequency plasma reactor

We present a numerical modeling of plasma-enhanced chemical vapor deposition (PECVD) of silicon film from SiH/sub 4/ and H/sub 2/ gas mixtures in very-high-frequency (VHF) plasma reactor. The model is composed by electron impact, gas-phase, and surface reactions in a well-mixed reactor model. A set of plasma parameters such as electron density, electron temperature and electron impact reaction rates is determined separately by nonequilibrium plasma model and used as inputs for well-mixed reactor models. The gas-phase reactions include electron impact and neutral-neutral reactions. Some of unknown rates of surface reactions are determined using quantum chemical calculations and transition state theory. In well-mixed reactor models, concentrations of each chemical species are calculated in a steady state condition using mass conservation equation uniformed through the reactor. Numerical results of growth rate as a function of plasma reactor operating parameters show good agreement with experimental ones. Finally optimal operating parameters are investigated using our model combined with design of experiments and optimization techniques.

Application of numerical analysis techniques to eddy current testing for steam generator tubes

Abstract This paper describes the application of numerical analysis to eddy current testing (ECT) for steam generator tubes. A symmetrical and three-dimensional sinusoidal steady state eddy current analysis code was developed. This code is formulated by future element method-boundary element method coupling techniques, in order not to regenerate the mesh data in the tube domain at every movement of the probe. The calculations were carried out under various conditions including those for various probe types, defect orientations and so on. Compared with the experimental data, it was shown that it is feasible to apply this code to actual use. Furthermore, we have developed a total eddy current analysis system which consists of an ECT calculation code, an automatic mesh generator for analysis, a database and display software for calculated results.

Effects of Facet Growth and Nucleation on Microcrystalline Silicon by Numerical Model

We have presented a model of microcrystalline silicon (μc-Si) growth based on the Van der Drift model. The model needs growth velocities of the facets (100) and (111), an amorphous silicon growth velocity and a grain nucleation rate. The growth velocity ratio of the facets, (100) and (111), determines the preferred orientation and the morphology of the μc-Si film, especially oriented to (110). As the grain nucleation rate increases, the ratio of the living grain number to the total grain number decreases and the crystallinity increases, so the grain nucleation rate governs the trade-off relation of the μc-Si cells between decreasing the open circuit voltage and increasing the short circuit current as the crystallinity increases.

Two-Dimensional Nonequilibrium Plasma Modeling Based on the Particle-Boltzmann Hybrid Model for RF Glow Discharges

A two-dimensional self-consistent nonequilibrium numerical method based on the particle and Boltzmann equation hybrid model has been developed to study the radio-frequency (rf) glow discharge. In this paper, the presented particle-Boltzmann hybrid model has been applied to two types of rf glow discharge. One is the parallel-plate capacitively coupled plasma (CCP) of Ar gas. The model predicted the spatial profile of Ar(3p5) density, which shows good agreement with the experimental emission profile of ArI (λ=419.8 nm). The other is the ladder electrode inductively coupled plasma (LICP) of SiH4 gas. It is found that electrons obtain their energy from both the electrostatic field enhanced by the edge effect and the induced electric field.