A hybrid kinetic Monte Carlo method for simulating silicon films grown by plasma-enhanced chemical vapor deposition

We present a powerful kinetic Monte Carlo (KMC) algorithm that allows one to simulate the growth of nanocrystalline silicon by plasma enhanced chemical vapor deposition (PECVD) for film thicknesses as large as several hundreds of monolayers. Our method combines a standard n-fold KMC algorithm with an efficient Markovian random walk scheme accounting for the surface diffusive processes of the species involved in PECVD. These processes are extremely fast compared to chemical reactions, thus in a brute application of the KMC method more than 99% of the computational time is spent in monitoring them. Our method decouples the treatment of these events from the rest of the reactions in a systematic way, thereby dramatically increasing the efficiency of the corresponding KMC algorithm. It is also making use of a very rich kinetic model which includes 5 species (H, SiH3, SiH2, SiH, and Si 2H5) that participate in 29 reactions. We have applied the new method in simulations of silicon growth under several conditions (in particular, silane fraction in the gas mixture), including those usually realized in actual PECVD technologies. This has allowed us to directly compare against available experimental data for the growth rate, the mesoscale morphology, and the chemical composition of the deposited film as a function of dilution ratio.open1

Electron-impact silane dissociation and deposition rate relationship in the PECVD of microcrystalline silicon thin films

An investigation of the relation between silane electron impact dissociation and deposition rates of microcrystalline silicon thin films, has been performed in highly diluted SiH4 in H2 discharges, by applying a combination of experimental measurements and modeling of the process. A wide range of frequencies (13.56 MHz - 50 MHz), power densities (11 mW/cm2 - 162 mW/cm2) and silane partial pressures (2% - 6%) at two total SiH4/H2 pressures of 0.5 Torr and 1 Torr has been studied. In the lower pressure, independent of all other discharge parameters, SiH4 primary dissociation has been found to be responsible for about 70% of the total silane consumption in the discharge, while a fraction of 12% of the initially produced silicon hydrides are incorporated into the growing film. The increase of pressure leads to a drop of the contribution of the SiH4 primary dissociation to the total silane consumption and to an increase of the deposition efficiency of the initially produced radicals to a value of 26%. This result is attributed to the production of additional, two silicon atom precursors via secondary gas-phase reactions

Treatment of polyethylene terephthalate in a He glow discharge

This work is focused on the study of electrical and optical properties of a helium glow discharge during the treatment of polyethylene terephthalate films for the modification of their surface properties. The experimental results reveal that the change of the polymer surface properties, due to the bombardment by energetic plasma species, is accompanied by a profound change of the electrical characteristics of the discharge and a spatially uniform quenching of certain emitting metastable species. The threshold-like evolution of these phenomena with increasing rf voltage indicates that they are likely to be attributed to ions accelerated in the polymer-covered electrode sheath

Effect of double-layers formation on the deposition of microcrystalline silicon films in hydrogen diluted silane discharges

The effect of the double layers formation on the gas-phase composition of SiH4/H2 discharges and the deposition rate of microcrystalline silicon thin films has been investigated by applying mass spectrometric and film growth measurements. Spatially Resolved Optical Emission Spectroscopy has been used for the detection of the appearance of this additional electron heating mechanism that in the present conditions results from the variation of either the discharge power or the total gas pressure. The experimental results have been in al1 cases combined to a gas phase and surface simulator of SiH4/H2 discharges allowing thus the discussion for the rather limited effect of this mechanism on the deposition process of µc-Si:H thin films