A new Langmuir probe structure using externally placed filters that can be tuned in the absence of plasma is proposed. The probe design and tuning procedure take into account especially the change in the probe's environment when plasma is turned on, thereby ensuring that the filters do not become detuned in the presence of plasma. Measurement of the RF voltage amplitudes in RF plasma using a calibrated capacitive probe gave, respectively, ≈15.7 V, ≈4.1 V, ≈2.1 V and ≈0.5 V at the fundamental frequency (≈13.56 MHz), the second, third and the fourth harmonics; based on these values a three-stage filter was built at the fundamental and the second and third harmonics. A complete analysis of the probe including its stray capacitance, RF equivalent circuit, filter and plasma impedance has been carried out, from which the maximum RF sheath voltage drop could be estimated as ≈0.27 V, ≈0.34 V and ≈1.30 V at the fundamental, the second harmonic and the third harmonic, respectively; the drop for the latter is somewhat large because of unexpectedly high loss in the filter components at the higher frequencies. I -V characteristics presented show that the floating potential of the probe decreases by ≈60 V, as the probe is detuned progressively from its tuned condition; also, the electron temperature increases from ≈1.7 to 3.5 eV with progressive detuning. It is worth noting here that although the method of calibrating the capacitive probe in this work is accurate for moderately high plasma densities (RF skin depth in plasma (= δ s ) small in comparison with the plasma dimension, L) its accuracy for lower densities (δ s ∼ L) is not too certain. Therefore, although the probe itself can be used at low plasma densities, verifying its efficacy for such cases could be difficult.

This work reports investigation of the Al-doped ZnO (AZO) film deposition process, at different working pressures, in a conventional magnetron sputtering system. The primary goal of this study is to investigate the plasma formation and deposition process using various diagnostic tools, by utilizing low-temperature deposition process. In addition, this paper also presents a systematic Langmuir probe (LP) analysis procedure to determine the maximum information about plasma parameters. For the present study, we have extensively used LP method to characterize the deposition process for the control of plasma parameters. Along with the LP method, we have also used optical emission spectroscopy diagnostic to examine the favorable deposition condition for the fabrication of conductive AZO film. Utilizing diagnostics, this also reports measurements of ion current density, substrate temperature, and deposition rates to fabricate low resistivity films of ∼3 mΩ cm.

This paper investigates the mechanisms by which the helicon and associated Trivelpiece-Gould waves are absorbed in helicon discharges produced in conducting chamber; the experiments were based on a recent theory of damping and absorption of helicon modes in conducting waveguides (Ganguli et al 2007 Phys. Plasmas 14 113503). In particular, it was also planned to investigate the manner in which the absorbed energy is utilized for the production of warm electrons that are needed for ionization because helicon discharges are high density, low T e discharges and the tail of the bulk electron population may not have sufficient high-energy electrons. To this end, two separate regimes were considered. The first was a low pressure (≈0.2-0.3 mTorr), low magnetic field (≈16-20 G) regime where both wave absorption and warm electron production are shown to proceed through Landau damping. The second was a moderate pressure (≈10 mTorr), moderate magnetic field (≈60-65 G) regime, where both power absorption (which is collisional) and warm electron production proceed via high-energy electrons produced by acceleration of bulk electrons (from neighboring regions) across large potential gradients.

This work presents a systematic plasma diagnostic approach for plasma processing using radio frequency (RF) and RF/UHF (ultra high frequency) hybrid plasmas. The present work also studies the influence of frequency on the deposition of Hydrogenated silicon nitride (SiNx: H) film using N2/SiH4/NH3 discharges. Analysis of data reveals that the UHF power addition to RF is quite effective in the plasma and radicals formation in different operating conditions. For the diagnostics, we have used optical emission spectroscopy, vacuum ultraviolet absorption spectroscopy, and RF compensated Langmuir probe. The presented diagnostic method directly exploits the optimized condition for fabricating high-quality silicon rich nitride (SiNx: H) thin film, at low temperature. With the help of hybrid plasmas, it is possible to fabricate SiNx: H film with high transparency ∼90%.

Hydrogenated nanocrystalline silicon (nc-Si : H) films intended for efficient nc-Si : H solar cells are usually made at the transition to the nanocrystalline regime using the plasma-enhanced chemical vapor deposition (PECVD) process. This change occurs within a sensitive process window and is affected by various deposition parameters. This paper reports a study of nc-Si : H films' fabrication by utilizing systematic plasma diagnostics. This work presents a novel approach for plasma processing using radio frequency (RF), ultra high frequency (UHF) and RF/UHF hybrid plasmas. Using careful analysis, efforts are made to investigate the radicals and plasma formation by changing the operating source power and silane (SiH 4 ) concentration. The aim of this work is also to investigate the PECVD process and conditions favorable for the synthesis of nc-Si : H film. For the present study, we systematically use the optical emission spectroscopy (OES), normal, and RF-compensated Langmuir probe (LP) and vacuum ultraviolet absorption spectroscopy diagnostics. Measurements reveal that the OES diagnostic is consistent with the LP measurements. Investigation reveals that UHF power in addition to RF enables higher dissociation of H or SiH radicals and the production of higher plasma density. The combined effect of both RF and UHF sources is used as the hybrid plasma source. Measurements also reveal that inbetween SiH 4 flow rates ∼20-30 sccm, there is significant change in the plasma characteristics that denotes the nc-Si : H−a-Si : H transition region. An atomic hydrogen density (n H ) in the range ≈ (8 − 10) × 10 11 cm −3 and plasma density n 0 ≈ (2 − 3) × 10 11 cm −3 with a silane to hydrogen ratio of 1-2% with high crystallinity has been obtained. Along with the discussion on the effect of frequency on plasma chemistry, this explains the RF power coupling and the role of electrons and ions in plasmas with increasing frequency.

The advanced materials process by non-thermal plasmas with a high plasma density allows the synthesis of small-to-big sized Si quantum dots by combining low-temperature deposition with superior crystalline quality in the background of an amorphous hydrogenated silicon nitride matrix. Here, we make quantum dot thin films in a reactive mixture of ammonia/silane/hydrogen utilizing dual-frequency capacitively coupled plasmas with high atomic hydrogen and nitrogen radical densities. Systematic data analysis using different film and plasma characterization tools reveals that the quantum dots with different sizes exhibit size dependent film properties, which are sensitively dependent on plasma characteristics. These films exhibit intense photoluminescence in the visible range with violet to orange colors and with narrow to broad widths (∼0.3-0.9 eV). The observed luminescence behavior can come from the quantum confinement effect, quasi-direct band-to-band recombination, and variation of atomic hydrogen and nitrogen radicals in the film growth network. The high luminescence yields in the visible range of the spectrum and size-tunable low-temperature synthesis with plasma and radical control make these quantum dot films good candidates for light emitting applications.

This paper presents a comprehensive overview of work on the helicon plasmas and also discusses various aspects of RF power deposition in such plasmas. Some of the work presented here is a review of earlier work on theoretical [A. Ganguli et al., Phys. Plasmas 14, 113503 (2007)] and experimental [A. Ganguli et al., Plasma Sources Sci. Technol. 20(1), 015021 (2011)] investigations on helicon plasmas in a conducting cylindrical waveguide for m = −1 mode. This work also presents an approach to investigate the mechanisms by which the helicon and associated Trivelpiece-Gould (TG) waves are responsible for RF power deposition in Helicon discharges. Experiment design adopts the recent theory of damping and absorption of Helicon modes in conducting waveguides [A. Ganguli et al., Phys. Plasmas 14, 113503 (2007)]. The effort has also been made to detect the warm electrons, which are necessary for ionization, because Helicon discharges are of high density, low Te discharges and the tail of the bulk electron population may not have sufficient high-energy electrons. Experimental set up also comprises of the mirror magnetic field. Measurements using RF compensated Langmuir probes [A. Ganguli et al., Plasma Sources Sci. Technol. 17, 015003 (2008)], B-dot probe and computations based on the theory shows that the warm electrons at low pressure (0.2–0.3 mTorr) Helicon discharges, are because of the Landau damping of TG waves. In collisional environment, at a pressure ≈10 mTorr, these high-energy electrons are due to the acceleration of bulk electrons from the neighboring regions across steep potential gradients possibly by the formation of double layers.

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