CHARACTERIZATION OF THE NEGATIVE-ION FRACTION IN HIGH-DENSITY SF6 MAGNETOPLASMAS USING ION-ACOUSTIC-WAVES

Most plasmas used in the microelectronics industry are electronegative , i.e., they contain a large number of negative ions. One simple way t o characterize the negative-to-positive ion density ratio (n(-)/n(+)) in such plasmas is to measure the velocity of ion acoustic waves (IAWs ). In this letter, a detailed study of the propagation of IAWs in high -density SF6 magnetoplasmas is given. Results (n(-)/n(+)) obtained by way of this technique as functions of different parameters (gas pressu re, SF6 content in SF6/Ar mixture, and radial position in the reactor) are compared to those obtained with a more sophisticated technique ba sed on laser photodetachment. (C) 1998 American Institute of Physics.