Kinetics of Radicals in CF 4 and C 4F 8 Electron Cyclotron Resonance Plasmas

Temporal variations in densities of CF and CF2 radicals were measured at rising phases of plasma ignition in CF4 and C4F8 electron-cyclotron-resonance (ECR) plasmas by infrared diode laser absorption spectroscopy. It was found that CF2 radical densities at the rising phase briefly became larger than those at the steady state in the C4F8 plasma. This finding shows that the CF2 is generated in abundance by the rapid dissociation of C4F8 molecules at the discharge ignition. The variations of CF2 and CF radical densities were demonstrated using a computer calculation to characterize the chemistry in the CF4 and C4F8 plasmas numerically. Chemical models in the CF4 and C4F8 ECR plasmas were presented based on the results obtained by the experiment and calculation. The models suggested that the higher fluorocarbons, that is CXFY (X ≥2), were important in the C4F8 plasma as dissociation paths from C4F8 molecules to CFX (X=1–3) radicals and as polymer precursors.