Operating modes of a magnetized cold cathode plasma in helium 50–6400 mTorr

Abstract

We characterize the operating modes of a magnetized cold cathode plasma in helium at pressures 50-6400 mTorr (6.7-850 Pa). We find at least three distinct modes: (i) a diffuse magnetron plasma with representative plasma voltage 250 V; (ii) a constricted mode with a bright spot at the cathode surface that moves slowly, with representative plasma voltage 50 V; and, (iii) a constricted mode (CO) with a bright spot at the cathode surface that orbits rapidly around the racetrack region defined by the magnetic field, with representative plasma voltage 80 V. This latter mode is of interest because it appears to be a cold-cathode plasma operating at unusually low voltage, and it is associated with a low rate of cathode massloss. We find that the CO mode appears only if the initial rate of current-rise is high, and if the cathode surface is smooth and featureless. It also appears to be correlated with cathode materials that form strong oxide films that can dramatically increase the field emission of electrons from the cathode surface.

Voltage and cathode emission mechanisms of a magnetized, constricted, orbiting plasma in helium 6.7–850 Pa

“…We found previously [7,8] that the plasma can operate in several distinct 'modes' that are distinguished by plasma voltage, cathode erosion rate, and visual appearance in high-speed imaging. One of the modes, termed 'constrictedorbiting' (CO), is the subject of this paper.…”

“…Several distinct structures then connect the moving dot to a semi-stationary diffuse glow that extends to the anode. Prior work [7] indicates that an oxide film on the cathode surface aids the formation of this mode.…”

“…One of the modes, termed 'constrictedorbiting' (CO), is the subject of this paper. The CO-mode plasma voltage is low for a cold-cathode helium plasma, 40-110 V, depending on pressure [7], and the CO-mode erosion rate is 0.01-0.1 of that expected for aluminium cathodes [8]. In high-speed imaging (3 × 10 4 frames s −1 ) the visual appearance of the CO-mode plasma is structured with a constricted attachment ('dot') to the cathode that moves (orbits) at high speed (∼300 m s −1 ) along the cathode surface in a circular path that is defined by the magnetic field.…”

Direct ion content measurements in a non-sputtering magnetron discharge

“…However, their stable operation requires special crossed electric and magnetic field geometry. These regimes characterized by high plasma densities and good spatial uniformity might be useful for semiconductor or polymer etching processes [6,7] as well as a possible concept for electric power switching [8].…”

Plasma parameters of a pulsed high-current low-voltage non-sputtering magnetron discharge in light gases

“…Depending on operating conditions (including pulse duration), it is possible to transform long HiPIMS regime (L-HiPIMS) into the non-sputtering low-voltage mode at the same power level. This mode is known as non-sputtering magnetron discharge (NSMD) [2][3][4]. Introducing hydrogen or helium into NSMD might result in high density plasma generation with extremely low cathode material erosion rate.…”