Vacuum-ultraviolet laser absorption spectroscopy for absolute measurement of fluorine atom density in fluorocarbon plasmas

Absolute density measurement of fluorine atoms has been performed by a vacuum-ultraviolet (VUV) laser absorption technique in fluorocarbon plasmas. A VUV laser tunable around 95 nm covering the resonance lines of F atoms has been produced in Xe gas by a two-photon resonance four-wave-mixing technique. In this method, the background absorption by the parent gases and species produced in the plasma can be eliminated by scanning the wavelength, and the absolute density of F atoms can be derived accurately from the integrated absorption line profile. The measured values of the density varied from 1×1011 to 4×1012 cm−3, depending on the source gas species and the operating conditions of an inductively coupled radio-frequency (400 kHz) discharge.