Comparison of the Fluorine Atom Density Measured by Actinometry and Vacuum Ultraviolet Absorption Spectroscopy

The validity of actinometry for measurement of fluorine atom density was examined by comparing the results with those obtained by vacuum ultraviolet absorption spectroscopy. The experiments were carried out in high-density CF4 and C4F8 plasmas excited by helicon-wave discharges. As a result, the error in the relative F atom density measured by actinometry was within a factor of ∼2 for the same working gas. On the other hand, the value of K in the actinometry relation n F = K n Ar (I F/I Ar) was considerably different between the CF4 and C4F8 plasmas. Hence evaluation of the absolute F atom density by actinometry is generally difficult, except for rough order-estimation by substituting K ≃2.