MEASUREMENT AND MODELING OF THE BULK PLASMA IN MAGNETRON SPUTTERING SOURCES

Langmuir probes have been used to diagnose the plasma above the ''race -track'' of a magnetron plasma source and the measurements compared wi th a simple, one-dimensional fluid model. The model is developed initi ally with two fluid components: plasma ions (created by electron-impac t ionization), which fall to the; sheath edge, and trapped thermal ele ctrons whose motion is mobility limited in the crossed E and B fields. Predictions show that with increasing magnetic field strength or decr easing ionization rate, a peak in density can occur close to the catho de, consistent with experiment. The model is then extended to allow fo r the possibility that energetic electrons may emerge from the sheath into the plasma. The results show that the magnitude of the sheath-edg e potential rises with increasing ''fast'' electron concentration. Abo ve a critical ''fast''-electron-to-ion density ratio, no sheath is pre dicted to form. Good agreement between experiment and prediction for t he plasma density variation demonstrates the usefulness of the one-dim ensional treatment as a first step to more complex modelling of the re gion. (C) 1997 Elsevier Science S.A.