Time-of-Flight Mass Spectrometry of Positive Ions in Helicon-Wave Excited High-Density CF_4 and C_4F_8 Plasmas

The composition of positive ions was investigated using a time-of-flight mass spectrometer in high-density CF4 and C4F8 helicon plasmas. For low (n e 8 ×1012 cm-3) electron densities, the dominant positive ions were C+ and F+ in both the CF4 and C4F8 plasmas. However, the C+/F+ ion current ratio was higher in the C4F8 plasma than the CF4 plasma. The reaction kinetics of positive ions is discussed based on the electron density dependence of the mass spectral intensities.