Diagnostic Study of an RF-Capacitively Coupled Plasma: The Breakdown of the Peripheral Gap Region

Abstract

Diagnostic studies of an rf-capacitvely coupled plasma driven by ring-shaped electrodes are performed with the focus of the investigation on the unintentional peripheral region breakdown. Upon this peripheral region breakdown, the radial profile of the electron density changes significantly from center-high to edge-high, as confirmed by the plasma appearance and by the surface temperature measurements. It is found that this breakdown is controlled by the gas type, pressure, power, and the gap between the grounding sample stage and the glass chamber wall. Among the factors, the gap appears to be the most critical one that controls this breakdown. The voltage at which this breakdown occurs increases with the decrease in the pressure and the gap size. In addition, argon plasmas show the lowest breakdown voltage, followed by nitrogen, oxygen, and helium plasmas. The above trends follow the left branch of the Paschen curve. We show that with a proper modification of the sample stage, a well-confined peripheral breakdown region with a high plasma density and a high degree of dissociation in O 2 plasmas can be formed.

Gas breakdown in radio-frequency field within MHz range: a review of the state of the art

“…In these applications, the value of breakdown studies varies: on the one hand, many applications need to prevent MRF breakdown from occurring, such as CCP, which is widely used in etching and deposition equipment, where dielectric rings are usually placed at large radii of the electrodes to improve the radial homogeneity of the plasma, and gas breakdown at the dielectric rings can lead to unstable discharges and the generation of impurities, thus requiring the avoidance of breakdown [18,19]. In addition, the reliable operation of MRF gas pedals also requires the avoidance of any gas or along-plane breakdown [20]; on the other hand, the MRF plasma widely used in industry is generated by lowpressure gas breakdown, and the breakdown voltage is usually higher than the steady-state voltage, and engineers must study how to break down the gas to generate plasma at low gas pressure and low RF voltage [20,21].…”