Gjh Seth Brussaard

Characterization of plasma beam deposited amorphous hydrogenated silicon

Fourier transform infrared spectrometry, visual transmission spectroscopy, and in situ ellipsometry have been performed on plasma beam deposited (PBD) amorphous hydrogenated silicon layers. From these measurements refractive index at infrared wavelengths and at 632.8 nm, the optical band gap and the hydrogen content of the layers have been determined. The hydrogen concentration of the layers varies between ∼9 and 25 at. %. It was found that the refractive index decreases more with hydrogen concentration in the layer than predicted by theoretical calculations assuming tetrahedral structures. The band gap of the material remains constant at ∼1.72 eV for the range of hydrogen contents measured. The resonance frequency of the SiH stretching mode (around 2000 cm−1) increases with increased hydrogen content. This is additional evidence to support the assumption that clustered SiH (SiH on voids) does not have its stretching mode near the 2100 cm−1 SiH2 peak. From the results presented it is concluded that PBD la...

Diagnostics of the magnetized low-pressure hydrogen plasma jet: Molecular regime

rotational temperature of the excited state H 2~d 2 P u) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher- a system of H 2 . The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to . 520 K. Several clear indications of presence of the ‘‘hot’’ electrons have been observed in the plasma: ~1! Langmuir probe measurements ~T e .1.4 eV!, ~2! appearance of the Fulcher-a system of H 2 ~excitation potential DE513.87 eV!, ~3! low rotational temperature ~T rot .260 K! of the excited H 2 ~d 3 P u ) molecules, ~4! local excitation in the plasma of Ar I~DE515.45 eV!, and Ar II~DE519.68 eV! spectral lines, ~5! local excitation in the plasma of He I~DE523.07 eV and DE524.04 eV! spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the ~1‐1.4!310 20 m 23 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%‐13%.

Photoconductive switching of a high-voltage spark gap

We have demonstrated photoconductive switching of a gas-filled spark gap. A femtosecond Ti:sapphire laser was focused in a 1 mm spark gap biased at 4.5 kV. There is a clear transition between triggered operation, when only part of the path between the electrodes is ionized, and photoconductive switching, when the entire length of the gap is ionized directly by the laser. The measured standard deviation of the time fluctuations between the rising edge of the transmitted electrical pulse and the laser was less than 15 ps.

Stripping of photoresist using a remote thermal Ar/O2 and Ar/N2/O2 plasma

Photoresist is etched using a remote thermal (cascaded arc) plasma in Ar/O2 and Ar/O2N2 mixtures. Very high etch rates, up to 200 nm/s, are achieved at low substrate temperatures (350 K) and low electron and ion temperatures (<0.5 eV). The addition of small amounts of nitrogen (3%) leads to an increase in etch rate. The etch rate in Ar/O2/N2 also increases with time during the etching process. The details of the plasma and surface chemistries are not yet well understood.

Experimental investigation of an atmospheric photoconductively switched high-voltage spark gap

We report on the experimental investigation of the photoconductively switched gas-filled spark gap. When the laser intensity of a femtosecond laser is high enough (around 1018Wm−2), a plasma can be created that spans the complete distance between the electrodes. The gas-filled spark gap is then closed on a femtosecond time scale, similar to photoconductive switching of a semiconductor switch. Stochastic breakdown processes, such as avalanche and streamer formation that cause the breakdown in laser triggered spark gaps, are passed over, which results in faster rise time and less jitter. Measurements of the switched pulses as a function of laser energy were performed in a 1-mm gap at an applied voltage of 4.5 kV. A clear transition from triggering to switching was measured with increased laser energy. Measurements of the output pulses with the gap filled with nitrogen at 1 atm showed results very similar to measurements in air in the same gap. In the switching regime, the amplitude of the switched pulse did...

Carbon Nitride thin films prepared by a capacitively coupled RF plasma jet

Abstract Carbon nitride thin films have been downstream deposited from a nitrogen plasma beam sustained by a capacitively coupled discharge generated between a RF powered carbon electrode and a grounded carbon nozzle. The spectral emission of the plasma jet strongly exhibits the CN radical emission indicating that the deposition takes place via a mechanism involving the CN radical. The deposition process is enhanced by DC biasing the powered electrode. The films have been investigated by X-ray diffraction, infrared absorption spectroscopy and X-ray photoelectron spectroscopy. The results show that the films are amorphous and contain in a large extent carbon nitrogen bonds.

Ion densities in a high-intensity, low flow nitrogen–argon plasma

The plasma density in an expanding thermal plasma was determined using planar Langmuir probe measurements. The arc plasma was operated at low flow (500 standard cm3 per minute). It is shown that the decrease of density with increasing distance from the nozzle of the arc in an argon plasma can be explained by diffusion away from the expansion axis. The determined decay length is 10 cm. In the case that nitrogen is injected in the arc, the plasma density is lowered considerably due to charge exchange and dissociative recombination in the expansion. Because of the low electron density (1017 m−3) at a partial nitrogen flow larger than 10%, the dissociative recombination becomes slow. The main loss process of N2+ ions in this case is diffusion away from the plasma axis. The effective decay length found in the nitrogen plasma is 9 cm.

Electrodynamic simulations of a photoconductively switched high voltage spark gap

We present a full three-dimensional electrodynamic model to simulate a photoconductively switched high voltage spark gap. This model describes the electromagnetic field-propagation in a coaxial spark gap set-up, which determines the rise time of the switched pulse and reveals the influence of discontinuities, such as view ports, on the pulse shape and the rise time. Existing inductive lumped element and transmission line models, used to model laser-triggered spark gaps, are compared with our electrodynamic model. The rise time of the switched pulses in the different models does not differ significantly. In the electrodynamic simulation, a curvature of the electric field wave front is visible, resulting from the presence of non-TEM modes near the gap. Furthermore, oscillations on the output signal are revealed. These oscillations are caused by internal reflections on the inner and outer conductors. Our electrodynamic model is able to visualize the rise time evolution by monitoring the electric field-propagation in the gap region. The presence of view ports in the set-up increases the rise time at the output significantly and induces, owing to internal reflections, extra oscillations in the signal.

Evidence of charge exchange between N+ and N2(A3S+u) in a low-temperature nitrogen plasma

Abstract The emission from the first negative system, N 2 + ( B 2 Σ + u )→N 2 + ( X 2 Σ + g )+ hν , is studied in the flowing nitrogen afterglow of a DC arc plasma. Investigation of the spectrum shows overpopulation of the vibrational levels 6 and 7 of the excited molecular ion, N 2 + ( B 2 Σ + u ). Selective excitation of these levels is explained by a charge exchange reaction between atomic ions in the ground state and metastable molecules in the N 2 ( A 3 Σ + u ) state. The emitted intensity of the first negative system is shown to be linear with electron density n e for n e >2×10 16 m −3 , a higher-order dependence exists below this value. This is consistent with population of N 2 + ( B 2 Σ + u ) by atomic ions, N + .

An expanding thermal plasma for deposition of a-Si:H

A remote argon/hydrogen plasma is used to deposit amorphous hydrogenated silicon. The plasma is generated in a DC thermal arc (typical operating conditions 0.5 bar, 5 kW) and expands into a low pressure chamber (20 Pa) thus creating a plasma jet with a typical flow velocity of 10 3 m/s. Pure silane is injected into the jet immediately after the nozzle, in a typical flow mixture of Ar:H 2 :SiH 4 =55:10:6 scc/s. The electron temperature in the jet is low (typ. 0.3 eV) : silane radicals are thought to be produced mainly by hydrogen abstraction, but also by a sequence of dissociative charge exchange and consecutive dissociative recombination. In-situ ellipsometry yields refractive indices of 3.6–4.2 at 632.8 nm and growth rates of 10–20 nm/s. FTIR analysis yields a hydrogen content of 9–25 at.% and refractive indices of 2.7–3.3 in the infrared. The SiH density decreases with increasing hydrogen content, whereas the SiH 2 density increases. Above 11 at.%, the majority of hydrogen is bonded in the SiH 2 configuration. The optical bandgap remains constant at approximately 1.72 eV. The photoconductivity is of the order 10 1–6 (Ωcm) 1–6 and the photoresponse 10 6 .