The Effect of Discharge Chamber Geometry on the Characteristics of Low-Pressure RF Capacitive Discharges

Abstract

Abstract-We report the measured extinction curves and current-voltage characteristics (CVCs) in several gases of RF capacitive discharges excited at 13.56 MHz in chambers of three different geometries: 1) parallel plates surrounded by a dielectric cylinder ("symmetric parallel plate"); 2) parallel plates surrounded by a metallic cylinder ("asymmetric confined"); and 3) parallel plates inside a much larger metallic chamber ("asymmetric unconfined"), similar to the gaseous electronics conference reference cell. The extinction curves and the CVCs show differences between the symmetric, asymmetric confined, and asymmetric unconfined chamber configurations. In particular, the discharges exist over a much broader range of RF voltages and gas pressures for the asymmetric unconfined chamber. For symmetric and asymmetric confined discharges, the extinction curves are close to each other in the regions near the minima and at lower pressure, but at higher pressure, the extinction curve of the asymmetric confined discharge runs at a lower voltage than the one for the discharge in a symmetric chamber. In the particular cases of an "asymmetric unconfined chamber" discharge or "asymmetric confined" one, the RF discharge experiences the transition from a "weak-current" mode to a "strong-current" one at lower RF voltages than is the case for a "symmetric parallel-plate" discharge.

Radial structure of low pressure rf capacitive discharges

“…As is known [4,9,[25][26][27][28][29][30][31][32][33][34][35], a rf capacitive discharge may burn in two different modes: a weak-current (a-) and strong-current (gmode). In the a-mode the electrons acquire their energy for ionizing gas atoms in the rf field in the quasi-neutral plasma, the electron emission from the surface of the electrodes not playing a substantial role in the discharge sustainment.…”

“…In so doing we use the values of the electron temperature determined from the probe CVCs (employing the linear section of the graph of the electron current to the probe constructed to the semi-logarithmic scale). [4,9,[25][26][27][28][29][30][31][32][33][34][35] of the rf discharge (the curve for U rf ¼ 50 V, p ¼ 0.1 Torr and the curves for U rf ¼ 100 and 165 V, p ¼ 1 Torr) counting from the discharge axis, the electron temperature first remains constant or increases weakly. However on approaching the wall of the discharge tube the electron temperature T e increases abruptly, its maximum value exceeding T e near the discharge axis almost more than twice.…”

Normal regime of the weak-current mode of an rf capacitive discharge

“…The normal regime can be clearly observed in the experimental CVCs of low-pressure rf discharges in argon, oxygen and N 2 O in [16][17][18][19][20], but the authors of these papers did not study it in detail. Godyak et al [16,17] presented CVCs of an rf discharge at different argon pressure values, where at small discharge current values and pressure values above 1 Torr one can observe a section relating to the normal regime (without indicating it in the text).…”

“…However, the authors of [19] did not perform detailed measurements of the normal current density and did not give a theoretical description of the normal regime. The authors of [20] limited themselves to the indication of the existence of the weakcurrent mode normal regime in a symmetric rf discharge and an asymmetric unconfined chamber configuration.…”

Influence of electrodes area ratios and the discharge volume in RF capacitively coupled plasma

“…There are two type of CCPs RF discharge, symmetric discharge include two identical electrodes [5,6], whilst in asymmetric discharge systems the plasma formed between two unequal electrodes area, later create a dc voltage appears as a result for the different in electron and ion mobility, this attributes to the different mass between them. Some research study the influence of the geometry design on the characteristics of CCP discharge with different gases as well as observed by using the different electrodes area ratio which play important role in dcself bias [7][8][9][10]. Gottscho et al, [8] showed that the discharge structure in CCP system contains the layers sandwiches (sheathplasma-sheath) usually formed with frequency well known 13.56 MHz in Argon plasma and the two sheaths at both of the two electrodes discharge can be described as a pure capacitive properties, in addition to this study gave very important results about the effects in the CCP discharge when using a different electrodes area ratio.…”