2-DIMENSIONAL LASER-INDUCED FLUORESCENCE IMAGING OF METASTABLE DENSITY IN LOW-PRESSURE RADIO-FREQUENCY ARGON PLASMAS WITH ADDED O-2, CL-2, AND CF4

The effect of minor additions of O-2, Cl-2, and CF, on the argon metas table relative density and spatial distribution in low-pressure, radio -frequency argon plasmas, generated within a parallel-plate Gaseous El ectronics Conference reference reactor, has been investigated using pl anar laser-induced fluorescence imaging. For the conditions examined ( 33.3 Pa, 75-300 V, <10 W), the addition of only a few percent of these electron attaching gases was found to decrease the metastable density by as much as an order of magnitude, despite the fact that the excite d-state argon emission indicated an increase in the metastable product ion rate. In the dilute O-2/Ar discharges examined here, the spatial d istribution of metastables was similar to that of the electropositive, pure argon cases, exhibiting a strong axial peak near the interface b etween the plasma bulk and the sheath at the powered electrode. In con trast, the addition of either Cl-2 or CF4 was found to significantly m odify the spatial distribution of the emission intensity and metastabl e density, resulting in a more symmetric and uniform axial metastable distribution. This change in metastable distribution for these mixture s was particularly apparent at lower powers and/or higher Cl-2/CF4 con centrations, and suggests a transition from an electropositive to a so mewhat electronegative discharge.