AVS 56th International Symposium & Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS-ThP

Paper PS-ThP18
Diagnostic Study of an rf-capacitively Coupled Plasma: The Breakdown of the Periphery Gap Regime

Thursday, November 12, 2009, 6:00 pm, Room Hall 3

Session: Plasma Science Poster Session
Presenter: H.W. Chang, National Taiwan University, Taiwan
Authors: H.W. Chang, National Taiwan University, Taiwan
C.C. Hsu, National Taiwan University, Taiwan
Correspondent: Click to Email
A diagnostic study of a radio-frequency capacitively coupled plasma of Ar, O2, N2, and He was performed to investigate the mechanism that dominates the breakdown of the periphery gap region. This plasma chamber has a cylindrical glass chamber with annular ring-shaped, powered electrodes with an adjustable height and a planar sample stage that serves as the grounding electrode. A voltage probe and a current probe were used to monitor the electrical characteristics of this plasma, and an optical emission spectrometer was used to monitor the optical emission spectra of the plasma. It is shown that as the (peak-to-peak) voltage at the powered electrode exceeds a critical value, the ignition in the region between the glass chamber wall and the grounding electrode occurs. Such a breakdown potentially leads to unstable and non-uniform discharge. A drop of the current and voltage were found to accompany the periphery region breakdown, and it was found that the pressure, gas type, and gap size are the decisive factors that dominate such a breakdown. The breakdown voltage increases with the decreases of the gap and with the decreases of pressure: in an Ar discharge under 80 mtorr, the breakdown voltage increases from 280 to 972 V as the sample stage-glass chamber wall gap decreases from 7 to 5 mm. Under 5 mm gap and 100 mtorr, the voltage at which the periphery region breakdown occurs for Ar, N2, and O2 are 577, 1470, and 2444 V while no breakdown occurs in He plasmas with the voltage up to 2560 V. While such a breakdown seems undesired in materials processing, we will show that a well-controlled transition could potentially be used to obtain a localized high-density region that could be useful for materials processing.