PLASMA DIAGNOSTICS AND PROCESSINGS IN CF4 HE RADIO-FREQUENCY DISCHARGE/

Plasma diagnostics and Si etching were carried out in 13.56 MHz rf CF4 plasma mixed with He. In the plasma diagnostics, density of ion flux reaching electrode, and both ion sheath thickness and de self-bias vol tage at powered electrode were measured. A small amount of He admixtur e in the CF4 plasma scarcely affects the plasma characteristics, but t hose greatly change when a few percent of CF4 is added into a He plasm a: the ion sheath thickness greatly decreases and the self-bias voltag e increases. This remarkable change was considered to be due to the CF 4/He discharge becoming electronegative. The He admixture can produce additional CFn+ ions by deexcitation processes with both excited He a toms and He+ ions, which affect considerably the Si etching rate and e tching anisotropy in plasma etching process. (C) 1997 American Vacuum Society.