Expanding the operating space for pulsed ICP sources via matchless power delivery*

The replacement of a conventional impedance-matched RF power delivery system with a matchless RF pulser enables power deposition without losses due to impedance mismatch driven power reflection. This can broaden the operating space for plasma reactors driven by pulsed RF by allowing for higher peak powers and lower duty cycles. The rate of rise of the electron density in an impedance matched plasma reactor is slower than the theoretical ideal because of a delay induced by the impedance matching network. Using an RF source that drives at the resonant frequency of the circuit, rather than using variable capacitors to change the circuit, enables power delivery without this mismatch driven inefficiency. The rate of rise of the electron density on the same ICP source was compared between cases with a traditional matching network and with a matchless pulsed system, ceteris paribus, in order to quantitatively determine the matching system delay. This power delivery approach enables operating with duty cycles lower than 1%, facilitating the achievement of very high peak powers. Peak power densities of 25 W/cm3 have been achieved in an argon plasma, which is approximately five times larger than those of typical plasma chambers used for etching purposes.