Radio Frequency Hollow Cathode Discharge Research Articles

Erratum to: Experimental and Theoretical Optimization of Radio Frequency Hollow Cathode Discharge

Erratum to: Experimental and Theoretical Optimization of Radio Frequency Hollow Cathode Discharge

Experimental and Theoretical Optimization of Radio Frequency Hollow Cathode Discharge

In this paper, the electron density in radio frequency (RF) hollow cathode discharge (HCD) is investigated in experiments and in simulation based on two-dimensional (2D) fluid model. The role of hole diameter on plasma density in RF HCD have been explored at various gas pressures. It is found that the optimal hole size for maximum plasma density decreases along with the increase of gas pressure, which is confirmed by simulated results. The simulations reveal that the high plasma density is owing to the hollow cathode effect in the hollow cathode. It is obtained that the optimal hole diameter in RF HCD is approximately sum of twice thickness of plasma sheath and triple the electron-neutral mean free path.

PIC/MCC Simulation of Radio Frequency Hollow Cathode Discharge in Nitrogen**supported by Natural Science Foundation of Hebei Province, China (No. A2012205072)

A two-dimensional PIC/MCC model is developed to simulate the nitrogen radio frequency hollow cathode discharge (rf-HCD). It is found that both the sheath oscillation heating and the secondary electron heating together play a role to maintain the rf-HCD under the simulated conditions. The mean energy of ions (N2+, N+) in the negative glow region is greater than the thermal kinetic energy of the molecular gas (N2), which is an important characteristic of rf-HCD. During the negative portion of the hollow electrode voltage cycle, electrons mainly follow pendulum movement and produce a large number of ionization collisions in the plasma region. During the positive voltage of the rf cycle, the axial electric field becomes stronger and its direction is pointing to the anode (substrate), therefore the ions move toward the anode (substrate) via the axial electric field acceleration. Compared with dc-HCD, rf-HCD is more suitable for serving as a plasma jet nozzle at low pressure.

Numerical simulation of the sustaining discharge in radio frequency hollow cathode discharge in argon

In this paper, a two-dimensional fluid model was developed to study the radio frequency (RF) hollow cathode discharge (HCD) in argon at 1 Torr. The evolutions of the particle density distribution and the ionization rate distribution in RF HCD at 13.56 MHz indicate that the discharge mainly occurs inside the hollow cathode. The spatio-temporal distributions of the ionization rate and the power deposition within the hollow cathode imply that sheath oscillation heating is the primary mechanism to sustain the RF HCD, whereas secondary electron emission plays a negligible role. However, as driving frequency decreases, secondary electron heating becomes a dominant mechanism to sustain the discharge in RF hollow cathode.

Theoretical investigation of plasma immersion ion implantation of cylindrical bore using hollow cathode plasma discharge

Plasma immersion ion implantation of the internal surface of a cylindrical bore with a small diameter is difficult. The use of radio-frequency hollow cathode discharge as the internal plasma source for ion implantation is proposed. The implantation dynamics and plasma sheath expansion are investigated numerically using the particle-in-cell model. The inner diameter of the tube in our simulation is 20 mm and the external diameter of the hollow cathode is 12 mm. Three electric field zones are observed due to the existence of the electrode with ground potential in the tube. The ions undergo acceleration in the region close to the hollow cathode, maintain their velocity in the zone without the electric field due to overlapping of the plasma sheath, and decelerate in the region near the open end of the tube. Most of the ions are implanted into the surface away from the open plane of the hollow cathode. This is attributed to the special configuration of vertical electric field. The simulation results have demonstrated that plasma immersion ion implantation using a hollow cathode can be effectively applied to the treatment of the inner wall of a cylindrical bore, especially the ones with a small diameter.

The Radio Frequency Hollow Cathode Discharge Induced by the RF Discharge in the Plasma-Jet Chemical Reactor

In the recent decade an RF driven, low-pressure plasma reactor with supersonic plasma jet was developed (RPJ). This reactor was successfully used for deposition of thin films of various materials. The deposition of thin films indicates that the properties of the deposited films are dependent on the sputtering or reactive sputtering processes appearing inside the nozzle (hollow cathode). The nozzle (hollow cathode) fabricated of different kinds of materials and alloys works both as a cathode of the radio frequency (RF) hollow cathode discharge and as a nozzle for plasma jet channel generation as well. The RF hollow cathode discharge is a secondary discharge, which is induced by the primary RF plasma generated in the reactor chamber. The present paper deals with the experimental study of this RF hollow cathode discharge. The stress is laid on the investigation of the axial distribution of discharge parameters and sputtering processes inside the nozzle. On the base of experiments, the simple model of the axial distribution of the investigated RF hollow cathode discharge has been developed.

The Radio Frequency Hollow Cathode Discharge Induced by the RF Discharge in the Plasma-Jet Chemical Reactor

In the recent decade an RF driven, low-pressure plasma reactor with supersonic plasma jet was developed (RPJ). This reactor was successfully used for deposition of thin films of various materials. The deposition of thin films indicates that the properties of the deposited films are dependent on the sputtering or reactive sputtering processes appearing inside the nozzle (hollow athode). The nozzle (hollow athode) fabricated of different kinds of materials and alloys works both as a cathode of the radio frequency (RF) hollow cathode discharge and as a nozzle for plasma jet channel generation as well. The RF hollow cathode discharge is a secondary discharge, which is induced by the primary RF plasma generated in the reactor chamber. The present paper deals with the experimental study of this RF hollow cathode discharge. The stress is laid on the investigation of the axial distribution of discharge parameters and sputtering processes inside the nozzle. On the base of experiments, the simple model of the axial distribution of the investigated RF hollow cathode discharge has been developed.

Comparison of the radio frequency hollow cathode to the microwave antenna discharge for plasma processing

Two nonconventional systems, the radio frequency hollow cathode discharge (RHCD) and the microwave antenna discharge (MWAD), with almost identical geometry of electrodes generating a nitrogen plasma at power level up to 60 W were compared. Both systems were used for deposition of nitride films at similar experimental parameters. The Al–N films were deposited in the RHCD system by reactive physical vapor deposition (PVD) using an Al radio frequency hollow cathode and the CNx films were deposited in the MWAD system by plasma activated chemical vapor deposition (PACVD) from N2+1% (alternatively 0.5% or 0.4%) C2H2 gas mixtures. The vibrational temperatures of nitrogen molecules in both systems were compared as functions of experimental parameters and discussed with respect to the film growth rates in the particular systems. It was found that irrespective of frequency difference of two orders of magnitude the vibrational temperatures of nitrogen molecules were similar, between 3000 and 4600 K, in both systems at similar experimental conditions. However, shapes of dependences of the vibrational temperature on particular parameters were different, due to different plasma generation principles. The nitride film growth rates were found to correlate to the vibrational temperatures of nitrogen molecules, but their dependences on experimental parameters were affected by specific features of the plasma generation in individual systems as well as by different mechanisms of the PVD and the PACVD of films.

Radio frequency hollow cathode discharge for large-area double-sided foil processing

A radio frequency (13.56 MHz) cold hollow cathode discharge (HCD) plasma source has been developed for double side surface treatment of foils, membranes, and textile products. A membrane with up to 30 cm width can be moved between two symmetrical, capacitively coupled active radio frequency (rf) electrodes (cathodes). The hollow cathodes consist of a number of parallel troughs separated with ribs oriented perpendicular to the direction of membrane motion. The troughs are open at both ends to establish an electrical contact between the plasma in hollow cathode troughs and the rf grounded electrodes (anodes). Two modes of plasma source operation are observed: diode discharge—comparable to the typical capacitively coupled two electrode rf discharge, and the much more intensive HCD. The HCD mode of operation can be sustained for a pressure range from 0.01 to 4 mbar for argon and from 0.01 to 0.2 mbar for oxygen. The influence of the geometry (trough width), of the cathode surface material (aluminum and alumina), and gas (argon and oxygen) on the source performance was investigated. The ignition pressure of the HCD decreases with increasing trough width and is higher for oxygen than for argon. Ion concentration and electron temperature distributions along the trough were measured by use of a double Langmuir probe. Maximum ion concentrations 1.4×1011 cm−3 for argon and 0.8×1011 cm−3 for oxygen at rf powers as low as 100 W were achieved. The ion concentration increases for a diode discharge and decreases for a HCD, when the hollow cathode surfaces are covered with thin plates of alumina. Electron temperatures twice as high for the HCD operation mode (8 eV) than for diode discharge operation mode (4 eV) are typical.