Absolute fluorine atom densities in fluorocarbon high-density plasmas measured by appearance mass spectrometry

We report absolute fluorine atom (F) density measurements based on appearance mass spectrometry (AMS). A liquid nitrogen cold trap installed in a mass spectrometer dramatically reduces background noise at m/e = 19 (F+), enabling reliable AMS measurement of F density. The F density reaches similar to 10(19) m(-3) in high-density inductively coupled plasmas in 100 % CF4 or C4F8 while addition of 50 % hydrogen decreases the F density by one order of magnitude. A conventional actinometry technique results in a factor of similar to 4 greater reduction of F density in comparison with the AMS result. High etch selectivity of SiO2 to Si is achieved for the radical density ratio CFxF larger than 25 (x=1-3).