Effects of Added O2 upon Argon Emission from an rf Glow Discharge

Abstract

Emission and absorption measurements have been made in rf glow discharges through pure argon and through argon with 1% O2 added. The results indicate that added O2 reduces the amount of excitation of neutral argon, particularly the concentration of metastable atoms. At the same time, increased emission is observed from argon ions when O2 is added. This is attributed to an increase in the argon ion concentration. The results of these experiments have important implications regarding the mechanisms operative in rf sputtering processes. Namely, under the conditions studied (rf power density of 10 W/cm2 and argon pressure 4×10−2 Torr) direct electron impact ionization appears to be the predominant maintenance mechanism of the glow rather than ionization resulting from metastable atom collisions. In addition, it is proposed that addition of oxygen to the argon discharge atmosphere serves to increase the secondary electron emission coefficient of the fused silica target.