To process large-scale integrated circuits, engineers must control the density of fluorine atoms to etch SiO2. Researchers at Kyoto University in Japan have proposed a means of assessing the fluorine density using a vacuum-ultraviolet laser absorption technique. In an experimental setup, the scientists used a two-photon resonance four-wave mixing process with xenon gas to produce a continuously tunable UV source at 95 nm. The background absorption by the parent gases and species produced in fluorocarbon plasmas can be eliminated by scanning the wavelength. Using the integrated absorption line profile, the researchers determined the absolute density of fluorine atoms. Details of the work were published in the April 19 issue of Applied Physics Letters.