Paper PS2-ThM2
Ballistic Electrons and Resulting EEDf in a DC+RF Hybrid CCP Reactor

Thursday, November 12, 2009, 8:20 am, Room B2

The DC+RF Hybrid is a capacitively coupled plasma (CCP) etcher with RF applied to the wafer electrode and a high-negative DC voltage on the opposite electrode 3cm away. Ion-secondary-electrons from the DC electrode are accelerated by the DC-sheath into the plasma as ballistic electrons. Gridded energy analyzers are placed behind the RF electrode for EEDf measurements. Experiment’s pressure-range varies from 30 mTorr to 70 mTorr with DC-voltage up to –1kV. EEDf reveals, (1) Maxwellian bulk, (2) ballistic electrons with energy corresponding to the applied DC-voltage, (3) a continuum from Maxwellian to the ballistic electron peak, (4) middle-energy electrons with distinct energy-peak. Measured EEDf qualitatively agree with PIC numerical experiment. The energy of the distinct middle-energy peak seems to depend on the sheath thickness and varies from ~ 40eV to 300eV. While ballistic electrons’ finite collisions contribute to the continuum, other non-negligible channel such as Landau-damped e^–-beam plasma waves, should be considered. The distinct middle-energy peak could result from Landau damping of a strong plasma wave of a specific wave number. The energy range of middle-energy peak is favorable in sustaining ionization, rendering the necessity of heating the Maxwellian bulk for a similar level of ionization.