A gas phase and surface simulator of highly diluted silane in hydrogen rf discharges used for the deposition of microcrystalline silicon has been developed. The model uses the spatial density distribution of SiH (X 2Π) radicals measured using laser induced fluorescence and the total silane consumption for estimating the primary electron induced silane dissociation, thus avoiding fluid or statistical approaches commonly used for the prediction of electron impact rate coefficients. A critical analysis is made for the relative importance of all the parameters involved either in the gas phase chemistry or in the surface processes. The model results are compared to experimental data concerning disilane production and film growth rate over a wide range of rf power densities in 2% and 6% SiH4 in H2 discharges. The good agreement between experimental and model results allows for the extension of the discussion to the composition of the radical flux reaching the substrate, the relative contribution of each of the radicals to the film growth, and the most probable mechanism of microcrystalls formation under typical conditions of low and high microcrystalline silicon deposition rate.

An improved method for the measurement of the power consumed in low pressure, radio frequency discharges is presented. The method involves the measurement of current and voltage waveforms outside the reactor, and the determination of the discharge impedance and the network of parasitics. The measured waveforms are transformed to the equivalent ones at the powered electrode, by using an electrical circuit model of the stray impedance of the cell, with experimentally determined components. A tunable shunt circuit is used for minimizing displacement currents. The equivalent circuit contains elements which account also for resistive power losses in the cell-shunt circuit. The obtained discharge power is compared with measurements of the total power output of the generator made by a power meter. Results concerning power consumption and impedance in argon and silane discharges are presented as a function of the excitation voltage and the pressure. In both cases there is a discharge impedance drop, for higher voltage or pressure, which leads to higher power consumption in the discharge. The measurements show that only a small, nonconstant part of the power is consumed in the discharge, whereas, the inclusion of resistive loses leads to more accurate results. The mechanisms of the discharge impedance drop are further discussed in terms of their relation to microscopic plasma phenomena and quantities.

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The effect of driving frequency (13.56–50 MHz) on the electrical characteristics and the optical properties of hydrogen discharges has been studied, under constant power conditions. The determination of the discharge power and impedance was based on current and voltage wave form measurements, while at the same time spatially resolved Hα emission profiles were recorded. As frequency is increased, the rf voltage required for maintaining a constant power level is reduced, while the discharge current increases and the impedance decreases. Concurrently the overall Hα emission intensity decreases and its spatial distribution becomes more uniform. Further analysis of these measurements through a theoretical model reveals that frequency influences the motion of charged species as well as the electron energy and the electric field, resulting in a modification of their spatial distribution. Moreover, the loss rate of charged species is reduced, leading to an increase of the plasma density and to a decrease of the electric field. Under these conditions, the total power spend for electron acceleration increases with frequency, but combined to the higher electron density, leads to a drop of the average energy gained per electron, a drop of the mean electron energy, and an enhancement of the low-energy electron-molecule collision processes against high energy ones.

An investigation of the effect of the total gas pressure on the deposition of microcrystalline thin films form highly diluted silane in hydrogen discharges was carried out at two different frequencies. The study was performed in conditions of constant power dissipation and constant silane partial pressure in the discharge while using a series of plasma diagnostics as electrical, optical, mass spectrometric, and in situ deposition rate measurements together with a simulator of the gas phase and the surface chemistry of SiH4∕H2 discharges. The results show that both the electron density and energy are affected by the change of the total pressure and the frequency. This in turn influences the rate of high energy electron–SiH4 dissociative processes and the total SiH4 consumption, which are favored by the frequency increase for most of the pressures. Furthermore, frequency was found to have the weakest effect on the deposition rate that was enhanced at 27.12MHz only for the lowest pressure of 1Torr. On the other hand, the increase of pressure from 1to10Torr has led to an optimum of the deposition rate recorded at 2.5Torr for both frequencies. This maximum is achieved when the rate of SiH4 dissociation to free radical is rather high; the flux of species is not significantly hindered by the increase of pressure and the secondary gas phase reactions of SiH4 act mainly as an additional source of film precursors.

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Wetting experiments in PET/polar liquid systems performed at 25 °C in air have shown that the values of contact angle measured one day after PET treatment with He and He/O2 plasmas decrease significantly compared to the untreated PET. Higher oxygen content in the He plasma improves wetting, whereas the substrate bias and total gas pressure (500 and 750 mTorr) are of minor importance. The calculated absolute values of the surface energy of plasma treated PET films combined to XPS measurements proved that the surface modification enhances their polar component while the dispersive one remains practically unaffected. Moreover, the results have shown that only a part of the polar interactions contribute to the wettability performance assuming that all the dispersive components interact at the solid/liquid interface.

Spatial concentration profiles of ground-state SiH and electronically excited SiH* radicals are measured using laser-induced fluorescence and emission spectroscopy, respectively. The measurements are made in pure silane, as well as in mixtures with helium, hydrogen, and argon, in a capacitively coupled rf glow-discharge apparatus used for the deposition of a-Si:H. Low-power–low-depletion conditions are maintained throughout, whereas pressure is varied from 20 to 400 mTorr. Our observations indicate a close relationship between concentration profiles of the species and local electron energy distribution. We conclude that spatial concentration profiles represent stationary generation rates of the radicals. In the case of diluted silane the process is strongly influenced by diffusional transport of detected species to the deposition electrode. The dependence of this effect on dilution grade and buffer gas used is presented.