Numerical Simulation of Hydrogen Dilution Effects on Deposition of Silicon Film at Atmospheric Pressure Radio-Frequency Argon Silane Plasma

Based on the one-dimensional fluid model, the characteristics of homogeneous discharges with hydrogen diluted silane and argon at atmospheric pressure are numerically investigated. The primary processes of excitation and ionization and sixteen reactions of radicals with radicals in silane/hydrogen/argon discharges are considered. The effects of hydrogen dilution on the densities of species （e, H, SiH3^＋, SiH3^-, SiH3,） are analyzed. The simulation results show that the highest densities of e, Si113^＋, H, SiH3^-, SiH3 correspond to the optimal dilution concentration of H2. The deposition rate of μc-Si：H film depends on the SiH3 concentration, and atomic hydrogen in the plasma is found to play an important role in the crystallization fraction of the deposited films. This model explains the effects of H2 dilution on the deposition rate and crystallized fraction of μc-Si：H film growth.

Effect of Hydrogen Dilution on Growth of Silicon Nanocrystals Embedded in Silicon Nitride Thin Film by Plasma-Enhanced CVD

An investigation was conducted into the effect of hydrogen dilution on the microstructure and optical properties of silicon nanograins embedded in silicon nitride （Si/SiNx） thin film deposited by the helicon wave plasma-enhanced chemical vapour deposition technique. With Ar-diluted SiH4 and N2 as the reactant gas sources in the fabrication of thin film, the film was formed at a high deposition rate. There was a high density of defect at the amorphous silicon （a-Si）/SiNx interface and a relative low optical gap in the film. An addition of hydrogen into the reactant gas reduced the film deposition rate sharply. The silicon nanograins in the SiNx matrix were in a crystalline state, and the density of defects at the silicon nanocrystals （nc-Si）/SiNx interface decreased significantly and the optical gap of the films widened. These results suggested that hydrogen activated by the plasma could not only eliminate in the defects between the interface of silicon nanograins and SiNx matrix, but also helped the nanograins transform from the amorphous into crystalline state. By changing the hydrogen dilution ratio in the reactant gas sources, a tunable band gap from 1.87 eV to 3.32 eV was obtained in the Si/SiNx film.

Role of Hydrogen Dilution in the Low-Temperature Growth of Nanocrystalline Si:H Thin Films from siH_4/H_2 Mixture

Hydrogenated nanocrystalline silicon thin films were fabricated from Sill4 with H2 dilution at a low substrate temperature of 200℃ by the conventional plasma enhanced chemical vapor deposition technique. A high deposition rate over 0.75 nm/s can be achieved. Raman scattering spectral measurements revealed that the crystalline fraction and grain size increased with the increase in hydrogen dilution ratio. Fourier transform infrared spectrum measurements showed that the hydrogen content decreased and the Si-H bonding configuration changed mainly from Sill to Sill2 with the increase in hydrogen dilution ratio. This suggested that the hydrogen dilution played an important role in the low-temperature growth of nanocrystalline silicon thin film. The growth mechanism is discussed in terms of a surface diffusion model and hydrogen etching effects.

Preparation of hydrogenated microcrystalline silicon films with hot-wire-assisted MWECR-CVD system

Intrinsic hydrogenated microcrystalline silicon （μc-Si：H） films have been prepared by hot-wire-assisted microwave electron-cyclotron-resonance chemical vapour deposition （HW-MWECR-CVD） under different deposition conditions, Fourier-transform infrared spectra and Raman spectra were measured. Optical band gap was determined by Tauc plots, and experiments of photo-induced degradation were performed. It was observed that hydrogen dilution plays a more essential role than substrate temperature in microcrystalline transformation at low temperatures. Crystalline volume fraction and mean grain size in the films increase with the dilution ratio （R=H2/（H2＋SiH4））. With the rise of crystallinity in the films, the optical band gap tends to become narrower while the hydrogen content and photo-induced degradation decrease dramatically. The samples, were identified as μc-Si：H films, by calculating the optical band gap. It is considered that hydrogen dilution has an effect on reducing the crystallization activation energy of the material, which promotes the heterogeneous solid-state phase transition characterized by the Johnson-Mehl-Avrami （JMA） equation. The films with the needed structure can be prepared by balancing deposition and crystallization through controlling process parameters.

Numerical Simulation of VHF Effects on Densities of Important Species for Silicon Film Deposition at Atmospheric Pressure

The characteristics of homogeneous discharges in mixed gases of hydrogen diluted silane and argon at atmospheric pressure are investigated numerically based on a one-dimensional fluid model. This model takes into account the primary processes-excitation and ionization, sixteen reactions of radicals with radicals in silane/hydrogen/argon discharges-and therefore, can adequately represent the discharge plasma. We analyze the effects of very high frequency （VHF） on the densities of species （e, H, SiH3, SiH＋ and SiH2） in such discharges using the model. The simulation results show that the densities of SiH3, SiH＋, H, and SiH2 increase with VHF when the VHF ranges from 30 MHz to 150 MHz. It is found that the deposition rate of uc-Si：H film depends on the concentration of SiH3, SiH＋, SiH2, and H in the plasma. The effects of VHF on the deposition rate and the amount of crystallized fraction for uc-Si：H film growth is also discussed in this paper.