Optical emission intensity overshoot and electron heating mechanisms during the re-ignition of pulsed capacitively coupled Ar plasmas

Phase resolved optical emission spectroscopy (PROES) measurements were combined with measurements of the optical emission intensity (OEI) and electrical characteristics (RF current and voltage, power, and DC bias voltage) as a function of time during the re-ignition of Ar plasmas pulsed at 100 Hz and 10 kHz. The OEI exhibits a large overshoot at the 100 Hz pulsing rate even though no such overshoot is present in any of the electrical characteristics. The OEI overshoot occurs at a point in time when the RF power, voltage, DC bias voltage, and electron density are all smaller than they become later in the glow. PROES measurements in combination with the time resolved electrical characteristics indicate that the heating mechanism for the electrons changes during the time of the overshoot in the OEI from stochastic heating to a combination of stochastic and ohmic heating. This combination appears to enable a more efficient transfer of the electrical energy into the electrons.