Absolute density and reaction kinetics of fluorine atoms in high-density c-C4F8 plasmas

Absolute density and reaction kinetics of fluorine (F) atoms in high-density octafluorocyclobutane (c-C4F8) plasmas were examined using vacuum ultraviolet absorption spectroscopy. The F atom densities, corresponding to electron densities ranging from 1×1011 to 5×1012 cm−3, were 1×1012–5×1013 cm−3 for gas pressures of 2–7 mTorr and rf powers of 0.2–1.5 kW. The F atom density was linearly dependent on the electron density for ne<1.5×1012 cm−3. According to lifetime measurements in the afterglow, two decay processes were found in the F atom density: exponential (first-order kinetics) and linear (zero-order kinetics) decay components. The linear-decay component became significant at high gas pressures. The time constant of the exponential-decay component ranged from 5 to 100 ms, which corresponds to surface loss probabilities of 10−1–10−3. The surface loss probability varied inversely with the F atom density.