Peter Bletzinger

The Gaseous Electronics Conference radio‐frequency reference cell: A defined parallel‐plate radio‐frequency system for experimental and theoretical studies of plasma‐processing discharges

A “reference cell” for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.

Comparison of high-voltage ac and pulsed operation of a surface dielectric barrier discharge

A surface dielectric barrier discharge (DBD) in atmospheric pressure air was excited either by low frequency (0.3–2 kHz) high-voltage ac or by short, high-voltage pulses at repetition rates from 50 to 600 pulses s−1. The short-pulse excited discharge was more diffuse and did not have the pronounced bright multiple cathode spots observed in the ac excited discharge. The discharge voltage, current and average power deposited into the discharge were calculated for both types of excitation. As a measure of plasma-chemical efficiency, the ozone number density was measured by UV absorption as a function of average deposited power. The density of ozone produced by ac excitation did not increase so rapidly as that produced by short-pulse excitation as a function of average power, with a maximum measured density of ~3 × 1015 cm−3 at 25 W. The maximum ozone production achieved by short-pulse excitation was ~8.5 × 1015 cm−3 at 20 W, which was four times greater than that achieved by ac excitation at the same power level.

Experimental characteristics of rf parallel‐plate discharges: Influence of attaching gases

Electrical characteristics of parallel‐plate rf discharges were measured with the goal of obtaining quantitative information of the properties of the discharges, in particular the electrode sheaths. Measurements of the impedance characteristics at variable electrode spacing suggest a transition of the power deposition process from volume to electrode dominated at about 1 Torr in argon. By changing the secondary electrode emission coefficient of the electrodes, it could be shown that the power into electrons emitted from the electrodes is small compared to the total power input. Adding the attachers CF4, C2F6, and SF6 caused a large increase of the discharge impedance in the high‐pressure (volume power deposition) regime and shifted the transition to the electrode‐dominated power deposition regime to lower pressures. The impedance behavior versus pressure was modeled with a simple equivalent electrical circuit from which the characteristics of the electrode sheaths and their influence on the electrical cha...

Wave Nature of Moving Striations

Abstract : The results are presented of time and space resolved measurements on the response of the positive column of a low-pressure glow discharge to external perturbations. From these the profile, structure and the backward wave nature of moving striations are clearly indicated. A new method of solution to the equation originally presented by Pekarek (Proceedings of Sixth International Conference on Ionization Phenomena in Gases, v.2, p. 133) is shown to contain all of the experimental results including the dispersion of a pulse disturbance. A stability criterion is derived; especially useful is that the onset of striations in a discharge can be calculated from a quadratic equation. (Author)

Oxygen-free dry etching of α-SiC using dilute SF6:Ar in an asymmetric parallel plate 13.56 MHz discharge

Etch rates of up to 2200 A/min have been achieved on hexagonal silicon carbide (SiC) using dilute mixtures of SF6:Ar in a standard 13.56 MHz asymmetric parallel plate discharge. Furthermore, these etch rates have been realized with excellent pattern anisotropy profiles of approximately 1 at pressures in the range of 100–350 mTorr and the SF6 fraction at or below 50%. An understanding of the mechanisms responsible for the high etch rates in this simple, dilute, gas mixture can be achieved by considering the electrical characteristics of the radio frequency plasma. The conditions defining maximum etch rates are associated with peak fluorine ion and/or radical production, and can be defined entirely in terms of the relative current–voltage phase shift leading to optimal plasma impedance conditions and ultimately to maximal power deposition into the plasma. In addition, this study shows that the pervasive practice of utilizing oxygenated gas chemistries for SiC etching is not required, as previously thought, ...

Electric field and plasma emission responses in a low pressure positive column discharge exposed to a low Mach number shock wave

Low Mach number shock waves propagating through a low pressure, nonequilibrium positive column gas discharge have been observed to experience dispersion and velocity changes. It is shown that these effects depend on discharge polarity. Optical and electrical measurements are described which show further polarity-dependent effects in discharge light emission and changes in electrical properties. Using two types of probes, electrical measurements were made of both the global changes in discharge voltage and current and time resolved local electric field changes. The measured behaviors of discharge and shock wave point to very localized triple or quadruple layer electric sheaths connected with the propagating shock wave, which provide local enhanced ionization at the shock front which can sustain the discharge, at least during the short shock propagation time. The postulated density gradient driven large local recirculation current in the potential minimum near this sheath [H. S. Maciel and J. E. Allen, J. P...

High‐repetition‐rate closed‐cycle rare gas electrical discharge laser

The recently developed technology of high‐pressure molecular lasers has been combined with ultrahigh‐vacuum technology to develop a fast‐flow high‐pressure laser system capable of long‐duration closed‐cycle operation with rare gases. The system’s economy, reliability, and capability for long‐time operation at a high repetition rate make it suitable for avionics, space, and isotope separation applications. High‐repetition‐rate laser performance has been demonstrated in He–Xe, Ne–Xe, Ar–Xe, and Kr–Xe. Experimental results for high‐pressure He–Xe mixtures are given.

Influence of dielectric barrier discharges on low Mach number shock waves at low to medium pressures

For shock wave propagation in nonequilibrium plasmas, it has been shown that when the electron Debye length exceeds the shock wave discontinuity dimension, strong double layers are generated, propagating with the shock wave. Strong double layer formation leads to the enhancement of the local excitation, ionization, and local neutral gas heating which increases the shock wave velocity. It is shown that dielectric barrier discharges (DBD) in pure N2 also increase the shock wave velocity and broaden the shock wave. The DBD is considerably more energy efficient in producing these effects compared to a dc glow discharge and can operate over a wide pressure range. It is shown that these effects are also operative in the pure N2 discharge afterglow, allowing a wide range of pulse repetition frequencies.

Comparison of hydrogen atom density measurements in three types of discharges using H2–N2 gas mixtures

Two-photon laser induced fluorescence measurement of H atom density in %H2–%N2 gas mixture discharges has shown that the flux of H atom remains nearly constant over a wide range of gas compositions and pressures in three types of discharge devices. This unique feature is attributable to an efficient multiquantum N2 vibrational energy transfer to the dissociation of H2. This result shows that an appropriate choice of molecular gas mixtures can be used to extend the discharge operating conditions and device size scaling without compromising atom flux production.

Power deposition in H2 and H2N2 glow discharges

Abstract Analyses and experiments on the fractional dissociation of H 2 in glow discharges in pure H 2 , and in H 2 N 2 mixtures are reported. The fractional power deposited in the dissociation of H 2 calculated from the Boltzmann transport analysis compares well with that required by our experimental data for absolute H atom densities. The analysis also provides generic guidelines towards identification of dominant dissociation processes in molecular gas mixture discharges. The results for low current current glow discharges in H 2 N 2 mixtures show that the vibrational energy reservoir of N 2 (X 1 Σ g + , ν ) must direcly or indirectly be an important factor in the dissociation of H 2 .