Comparison of the identities, fluxes, and energies of ions formed in high density fluorocarbon discharges

Positive ion bombardment plays an essential role in plasma processing, influencing etch rates, materials selectivity and etching profiles. Experimental determination of ion identities and energies in processing plasmas provides complementary data necessary to validate the accuracy of plasma models, and contributes to a fundamental understanding of the underlying discharge physics and chemistry. We present a comparative summary of ion compositions and energy distributions in inductively coupled discharges sustained in six fluorinated compounds: CF4, CHF3, C2F6, c-C4F8, CF3I and CF3CH2F. Mass-resolved ion fluxes and energies are measured using a combined energy analyzer-mass spectrometer that samples ions extracted through an orifice in the lower electrode of an inductively coupled Gaseous Electronics Conference (GEC) rf reference cell. These compounds represent common plasma processing gases as well as two gases with significantly lower global warming potentials, CF3I and CF3CH2F. We compare the identities of the significant ions formed, the relative yields of CFx+ and secondary ions, the width and structure of the ion energy distributions, and the mean ion energies in these six plasma chemistries. The general effects of plasma operating conditions and Ar dilution on these properties are summarized