Study on electron heating and E-H mode transition in planar inductively coupled plasma

Abstract

Studies on electron heating are done during the rf power coupling change in the discharge mode transition (E-H mode transition) in a planar inductive discharge of 13 MHz without electrostatic screen (Faraday shield). An inert argon gas is used as the discharge gas and the operating pressure is fixed at 5 mTorr. The variation of the plasma impedance is measured by the commercial rf high-voltage probe and the home- made Rogowski coil. Also, the evolution of the electron energy distribution function (EEDF) is observed with an rf compensated Langmuir probe and the trend of its integrals, electron density and effective electron temperature, and especially plasma potential against rf power are presented. It is demonstrated that the plasma potential is gov- erned primarily by the high-energy electron tail in a plasma with bi-Maxwellian EEDF. The interdependence of the EEDF and the plasma potential is discussed. The experimental results show that the plasma potential against rf power reflects a change in the relative contribution of capacitive power coupling to electron heating. The study on the phenomena of the discharge mode transition from the E-mode to the H-mode in high-frequency (19 MHz) inductively coupled argon discharges is performed. Experimental observation is done at the low pressure of 10 mTorr and the high frequency of 19 MHz over a range of rf power, 40-525 W. First of all, the discharge mode transition is observed through a change of luminous intensity. On the other hand, the characteristics of the mode transition in a 6.5 MHz discharge is investigated for the purpose of the comparison with that in 19 MHz discharge. The transition in 19 MHz discharge is found to occur at the relatively high rf power of about 280 W compared with the mode transition in the 6.5 MHz discharge. Also, some distinctive features are compared to low- frequency discharges during this transition. In particular, during the E-H mode transition the apparent changes of plasma potentia...