Correlating transient plasma parameters to electrical measurements in pulsed R.F. discharges

Summary form only given. Electron density and electron temperature transients in pulsed RF discharges have been well characterized by several groups (1-3). These transients result in power coupling mismatch conditions which hamper power delivery accuracy and limit the integration of pulsed power delivery in some state of the art plasma source configurations, in particular those using multiple power supplies. To enable integration of pulsed power delivery in these systems, the electrical response of the plasma during transients is measured and compared to plasma conditions such as electron density, electron temperature, collision frequency, and sheath voltage; all of these contribute to the equivalent electrical impedance of the plasma as part of the RF power delivery circuit.A parallel plate reactor with 150 mm diameter electrodes and a gap of 25 mm is driven by a primary pulsed RF power supply and a supplemental CW low power supply that is used primarily for impedance measurements in the off cycle of the pulse event. Plasma properties including: optical emission, electron temperature, electron density, and sheath voltage are measured as a function of time within a pulsed RF cycle (13.56 MHz with a nominal 1 kHz pulse frequency and 30% duty cycle). A suite of diagnostics including a 0.5 m spectrometer, a RF compensated Langmuir probe, a gated ns resolution imaging system, and an in-line RF metrology tool capable of measuring voltage, current, and phase at 2ns time resolution are used to measure the plasma properties and electrical impedance of the discharge through the pulse cycle. The intent of this work is to correlate the time varying global plasma conditions to electrical impedance measurements and investigate pathways for advanced power matching that will enable extension of pulsed RF technology to a wider class of industrial plasma processes.