PLASMA-DIFFUSION FROM A LOW-PRESSURE RADIO-FREQUENCY SOURCE

Helicon sources are becoming a promising technique for providing high ion fluxes with controllable energy. It is still unclear how the plasma parameters evolve from the source to the diffusion chamber where the wafer is situated. To investigate this region electric probes have been used (Langmuir probe and energy analyzer) to measure electron temperature, plasma potential, plasma density, and ionic distribution functions along the axis of a symmetric Argon plasma diffusing freely away from a 6-cm-diam 20-cm-long, 13.56-MHz (Helicon) source operating at 10(-6) bar and 300 W. The plasma density and potential are simply related by Boltzman's relation. Although a potential difference of 37 V is measured between the source and the substrate, charge exchange collisions reduce the average energy of the ions arriving at the substrate to about 5 eV. This low energy should be advantageous in processing easily damaged thin films.