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A simple experimental method to estimate the power effectively absorbed by a plasma is presented. It relies on a thermal management study that is applied to the whole discharge system, providing the energy released by the plasma and lost by convection and radiation at the reactor walls. The methodology is illustrated in the case of H2 Electron Cyclotron Resonance microwave plasma. Nevertheless, this method can be extended to a variety of electrical discharge or feed gases. Using this method, an experimental coupling efficiency of ∼22 ± ∼8% was derived. In comparison, an analytical balance of the plasma power absorption yields a theoretical coupling efficiency of ∼28 ± ∼9%. [ABSTRACT FROM AUTHOR]

The design and characterization of a multi-dipolar microwave electron cyclotron resonance (ECR) hydrogen plasma reactor are presented. In this configuration, 16 ECR sources are disposed uniformly along the azimuthal direction at a constant distance from the center of a cylindrical reactor. Several plasma diagnostics have been used to determine key parameters such as neutral species temperature; electron density and temperature; and H+, H2+, and H3+ ion energy distributions. The experimental characterization is supported by electromagnetic and magnetostatic field simulations as well as Particle In-Cell Monte Carlo Collisions simulations to analyze the observed ion energy distribution functions. Especially, we show that both electron density and temperature are spatially uniform, i.e., 1011 cm−3 and 3 eV, respectively. This plasma enables generating ion flux and energy in the ranges 1019–1022 ions m−2 s−1 and few keVs, respectively. The H2+ ion distribution function shows two populations which were attributed to surface effects. These features make this reactor particularly suitable for studying hydrogen plasma surface interaction under controlled conditions. [ABSTRACT FROM AUTHOR]

One of the best ways to increase the diamond growth rate is to couple high microwave power to the plasma. Indeed, increasing the power density leads to increase gas temperature the atomic hydrogen density in the plasma bulk, and to produce more hydrogen and methyl at the diamond surface. Experimental and numerical approaches were used to study the microwave plasma under high power densities conditions. Gas temperature was measured by optical emission spectroscopy and H-atom density using actinometry. CH3-radical density was obtained using a 1D model that describes temperatures and plasma composition from the substrate to the top of the reactor. The results show that gas temperature in the plasma bulk, atomic hydrogen, and methyl densities at the diamond surface highly increase with the power density. As a consequence, measurements have shown that diamond growth rate also increases. At very high power density, we measured a growth rate of 40 μm/h with an H-atom density of 5 × 1017 cm–3 which corresponds to a H2 dissociation rate higher than 50%. Finally, we have shown that the growth rate can be framed between a lower and an upper limit as a function depending only on the maximum of H-atom density measured or calculated in the plasma bulk. The results also demonstrated that increasing fresh CH4 by an appropriate injection into the boundary layer is a potential way to increase the diamond growth rates. [ABSTRACT FROM AUTHOR]

Optical emission spectroscopy (OES), absorption measurements, and thermal energy rate analysis were used in tandem with numerical models to characterize microwave argon plasmas. A WAVEMAT (model MPDR-3135) microwave diamond deposition system was used to generate argon plasmas at 5 Torr. Three excited state number densities (4p, 5p, and 5d) were obtained from the OES measurements, and a fourth excited state number density (4s) was obtained from the absorption measurements. Further, power absorbed in the substrate was monitored. A self-consistent two-dimensional argon model coupled with an electromagnetic field model and a 25-level two-dimensional (2D)-collisional-radiative model (CRM) was developed and validated with the experimental measurements. The 2D model provides the gas and electron temperature distributions, and the electron, ion, and 4s state number densities, which are then iteratively fed into the electromagnetic and CRM models. Both the numerically predicted thermal energy rates and excited state densities agreed, within the experimental and numerical uncertainties, with the experimental results. [ABSTRACT FROM AUTHOR]

Zero-dimensional and two-dimensional plasma models and optical emission spectroscopy are used in tandem to investigate the power coupling efficiency for a pure hydrogen microwave plasma. The zero-dimensional model accounts for the vibrational kinetics of H[sub 2], the chemistry of H[sub 2] and H excited states, and the kinetics of ground-state species. The set of species conservation equations are then coupled to the electron Boltzmann equation (to account for the non-Maxwellian electron energy distribution function) and the total energy equation for solution. The two-dimensional model makes use of a simpler thermochemical description of the plasma. The chemistry is described with nine species and thirty chemical reactions. Three energy modes are considered to describe the plasma's thermal nonequilibrium, and Maxwellian distribution functions for kinetic and vibrational modes are assumed. The non-Maxwellian nature of the electron energy distribution function is separately accounted for. Experimentally, the absolute line emission intensity is utilized to obtain number densities of up to five hydrogen excited states using the following transitions: Hα (6563 Å), Hβ (4861 Å), Hγ (4340 Å), Hδ (4102 Å), and Hepsilon; (3970 Å). The first three transitions were used for a 38 Torr, 1000 W hydrogen discharge, and all five transitions were used for a 121 Torr, 4000 W hydrogen discharge. The absolute continuum emission from the plasma was compared to numerical predictions. The comparison of the numerical and experimental data indicates that 90%-100% of the input power is deposited in the plasma and that both the line and continuum emission match within a factor of 3, with the exception of the high energy excited states for the 4000 W plasma. A control volume heat transfer analysis validates the energy coupling. [ABSTRACT FROM AUTHOR]

Dust production kinetics and dust particle dynamics in low pressure (0.1–1 Pa) microwave electron cyclotron resonance acetylene plasmas are investigated experimentally using highly sensitive multi-pass laser extinction and scattering imaging techniques. We showed that despite the very low pressure, carbon dust nanoparticles are produced according to two routes: a homogeneous nucleation route leading to few tens of nanometers-size spherical particles and a heterogeneous route resulting in complex shape micrometer-size dust that are directly expelled from a carbon film deposited when the plasma is operated. We suggest that molecular growth involving positively charged ions may be the dominant mechanism underlying the homogeneous nucleation route for this magnetized plasma. Also, we showed that the dynamic of dust particles is mainly governed by thermophoresis force. [ABSTRACT FROM AUTHOR]

Abstract: The addition of a coating on the inside walls of a standard polyethylene teraphthalate (PET) bottle provides a gas barrier improvement of the packaging for beer, juice and carbonated soft drinks. Sidel Inc. has developed a plasma-assisted deposition process of hydrogenated amorphous carbon (a-C:H) films, which uses pulsed microwave discharges with acetylene gas precursor. We report here the space- and time-resolved optical diagnostics of this process, aiming to assess the microwave discharge characteristics and behavior during the deposition process. Time-resolved fast imaging of the discharge enables the investigation of plasma ignition, expansion and extinction inside the bottle along the microwave power pulses of 100 Hz frequency. Space- and time-resolved optical emission spectroscopy is used in order to examine the feature of the main radiative species within the plasma and to estimate the gas temperature. Measurements showed that the plasma emission intensity is always higher in the base and around the neck of the bottle, which comes from the discharge spatial inhomogeneity and from the successive phases of plasma development always involving the lower part of the bottle. The spatio-temporal intensity distribution of radiative species, namely H-atom and C2 molecule, is in good agreement with fast imaging, whereas the profile of CH radical is found to be more homogeneous. Rotational temperatures of excited states of C2 molecule and CH radical measured during a microwave pulse were found to be relatively high, between 1700 and 2700 K, and slightly dependent of time and position. A short heating time of only a few hundreds of microseconds is noticed and gives evidence of non equilibrium between the rotational temperatures and the gas temperature. This preliminary plasma diagnostic is a first step towards drawing possible connections between plasma characteristics and a-C:H coating properties and PET bottle post-treatment temperature, aiming at optimizing the deposition process. [Copyright &y& Elsevier]

Abstract: Several microwave reactors of various sizes were studied to quantify the size scaling behavior of microwave plasma-assisted CVD (PACVD) diamond deposition. All the systems studied were microwave resonant cavity based systems using predominantly hydrogen based discharges. The input variables considered include the microwave frequency (2.45 GHz and 915 MHz), the microwave power level, and the discharge chamber size (5–28 cm diameter). The substrate sizes for the various reactors studied ranged from 2.5 cm diameter substrates for the small reactor size to 15 cm diameter substrates for the large reactor size. The variables quantified in the diamond deposition process and reactor included the microwave discharge power density, discharge size, discharge gas temperature, as well as, measurements of diamond deposition area and rate. The discharge power density versus pressure and discharge size is quantified by experimental measurements and numerical modeling. Results show that as the discharge size increases the discharge power density decreases significantly at a given pressure. [Copyright &y& Elsevier]

Abstract: Optical emission spectroscopy has been used to characterize diamond deposition microwave chemical vapour deposition (MWCVD) plasmas operating at high power density. Electron temperature has been deduced from H atom emission lines while H-atom mole fraction variations have been estimated using actinometry technique, for a wide range of working conditions: pressure 25–400hPa and MW power 600–4000W. An increase of the pressure from 14hPa to 400hPa with a simultaneous increase in power causes an electron temperature decrease from 17,000K to 10,000K and a H atom mole fraction increase from 0.1 to up to 0.6. This last value however must be considered as an upper estimate due to some assumptions made as well as experimental uncertainties. [Copyright &y& Elsevier]

Abstract: The use of CVD diamond in electronics has very stringent requirements. For a CVD diamond industry to become viable it is mandatory to obtain very large growth rates (>5 µm/h), all the while maintaining extremely high purity, a crystalline defect density as low as possible, and large usable surface areas. At the same time, one must keep the stress level within the growing crystal below acceptable limits to avoid crack formation and preserve the crystal structural integrity. These imperatives imply to work to improve both the plasma deposition process and the CVD diamond crystal growth. In this paper, we propose a three-pronged approach: (i) We use detailed plasma models to establish the influence of process parameters (in particular deposition pressure) on plasma chemistry in order to optimize film growth rate and diamond quality; (ii) We emphasize the need for careful substrate pre-treatment and selection (including choosing a single-sector face) to minimize defects in the growing films; (iii) We employ a 3D geometrical model to predict the crystal shape under given growth conditions, and exploit this knowledge to devise a growth strategy maximizing the usable film surface area while minimizing stresses inside the films. [Copyright &y& Elsevier]