Studies of CF2 radical and O atom in oxygen/fluorocarbon plasmas by laser-induced fluorescence

Abstract

Laser-induced fluorescence 0LIF) has been used to examine behaviors of the CF2 radicals and O atoms in oxygen/fluorocarbon plasmas by utilizing a magnetic neutral loop discharge 0NLD), which is characterized by the efficient plasma production around the neutral loop, ‘NL region'. It was found that, in a pure CF4 plasma, the radial profile of CF2 density near the NL region changes from convex to concave with increasing rf power. This implies that the NL region is a source for CF2 at low rf powers and changes into a net sink at high rf powers, probablydue to the excess dissociation of CF2. In contrast, the O atom density in a pure O2 plasma was found to be very high and increases steadily against the rf power, corresponding to the dissociation degree of more than 20%. These features, emphasized by the high dissociation efficiency of the NLD, demonstrate different behaviors of both speciesrelated with the production and loss mechanisms. In plasmas of O2/ CF4 mixtures, it was found that the variation of O density as a function of gas composition is mostly linear, depending on the dilution factor, while thatofCF2 is nonlinear. This fact straightforwardly indicates that CF2 is mainly lost through reaction with O2 and that O is generated by the dissociation of residual O2. The change in the CF2 radial profile by O2 addition suggested that CF2 and O2 react in gas-phase and that the NL region fundamentally acts as a source for CF2. The results for O2/C4F8 plasmaswere also presented and understood with the same description as in O2/CF4 plasmas taking into account the compositional balance of C/O2 and the slow surface-loss process.