Electron energy distribution functions and the influence on fluorocarbon plasma chemistry

Two different modes of electron heating are found in microwave discharges: the bulk heating mode characterized with low electron density n(e) and high electron temperature T-e (similar to 10 eV), and the surface heating mode with high n(e) and low T-e (similar to3 eV). The correlation between the he ating mode and the electron energy distribution function (EEDF) is qualitat ively interpreted in terms of non-local kinetic theory, taking account of t he ambipolar potential well. A biased optical probe diagnostics of a surfac e wave plasma (SWP) reveals that the surface heating mode gives a bi-Maxwel lian type EEDF, that is, a sum of two Maxwellian distributions of bulk temp erature T-b and tail temperature T-t > T-b. On the other hand, the EEDF of inductively coupled plasma (ICP) is close to a single-Maxwellian distributi on with electron temperature higher than the bulk temperature Tb of the SWP . Such differences in the EEDFs make the composition of the reactive specie s of the two plasmas different; namely, ion and radical measurements at the same electron density show that the ICP contains more F radicals and less CF3 and CF2 radicals in comparison with the SWP. In addition, a simplified model based on the bi-Maxwellian EEDF shows how the EEDF determines the ion and radical compositions, supporting the major experimental results. These observations and calculations suggest that plasma chemistry is controllabl e by tailoring the EEDF with proper adjustment of bulk heating and/or surfa ce heating of electrons.