Change in the Heating Mechanism During the Early Stages of Re-Ignition of Pulsed Capacitively Coupled Ar Plasmas.*

We have made Phase Resolved Optical Emission Spectroscopy measurements in pulsed Ar plasmas and combined them with measurements of the optical emission intensity (OEI) and electrical characteristics. The OEI exhibits a large overshoot early in the re-ignition at the 100 Hz pulsing rate which is not reflected in any of the electrical characteristics or present at a 10 kHz pulsing rate. This 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 time resolved electrical characteristics indicate that the heating mechanism for electrons changes during the overshoot to a combination of stochastic and ohmic heating (from stochastic heating in the steady state). The combination enables a more efficient transfer of the electrical energy to heating electrons.