Foundations of DC plasma sources

Abstract

A typical dc discharge is configured with the negative cathode at one end and a positive anode at the other end, separated by a gas filled gap, placed inside a long glass cylinder. A few hundred volts between the cathode and anode is required to maintain the discharge. The type of discharge that is formed between the two electrodes depends upon the pressure of the working gas, the nature of the working gas, the applied voltage and the geometry of the discharge. We discuss the current-voltage characteristics of the discharge as well as the distinct structure that develops in the glow discharge region. The dc glow discharge appears in the discharge current range from µA to mA at 0.5 -300 Pa pressure. We discuss the various phenomena observed in the dc glow discharge, including the cathode region, the positive column, and striations. The dc glow discharge is maintained by the emission of secondary electrons from the cathode target due to the bombardment of ions. For decades the dc glow discharge has been used as a sputter source. Then it is often operated as an obstructed abnormal glow discharge and the required applied voltage is in the range 2 -5 kV. Typically, the cathode target (the material to be deposited) is connected to a negative voltage supply (dc or rf) and the substrate holder faces the target. The relatively high operating pressure, in the range from 2 -4 Pa, high applied voltages, and the necessity to have a conductive target limit the application of dc glow discharge as a sputter source. In order to lower the discharge voltage and expand the operation pressure range the lifetime of the electrons in target vicinity is increased through applying magnetic field, by adding permanent magnets behind the cathode target. This arrangement is coined the magnetron sputtering discharge. The various configurations of the magnetron sputtering discharge and its applications are described. Furthermore, the use of dc discharges for chemical analysis, the Penning discharge and the hollow cathode discharges and some of its applications are briefly discussed.

Argon self‐organized striation plasmas under kPa pressure level

“…The bright layer of striation corresponds to an area with a predominant generation of great concentrations of excited atoms and ions and the dark layer of striation corresponding to particle loss due to ambipolar diffusion to the discharge tube walls and recombination is predominant. [5] The striations are divided into moving striations and standing striations. Moving striations are usually observed in noble gases, whereas standing striations are typical for molecular gases and in mixtures of molecular and rare gases.…”

Plasma Synthesis and Self-Assembly of Magnetic Nanoparticles

“…The technique is relatively cheap since the requirements of the power supply is quite low, and the reproducibility is high due to the simplicity of its layout. [17]…”

Gas breakdown and its scaling law in microgaps with multiple concentric cathode protrusions

“…The breakdown point is identified when the discharge enters the subnormal glow regime with a negative differential resistance. 46 In Fig. 2(a), for the case p ¼ 500 Torr, a ¼ 50 lm, b ¼ 25 lm, X ¼ 100 lm, d max ¼ 200 lm, and R ¼ 500 lm, the breakdown point is reached when U dc ¼ 147 V. Using this method, the breakdown voltage can be quantified with very small uncertainties and alternative criteria avoided.…”