Ion and neutral species in C2F6 and CHF3 dielectric etch discharges

Relative concentrations of reactive ions, neutral radicals, resist and subs trate etch products have been measured in dielectric etch chemistries using an uncollided beam mass spectrometer/ion extractor from Hiden Analytical. Analysis techniques employed include both electron impact ionization and di ssociative ionization of neutral gas, and potential bias extraction of posi tive ions from the reactor discharge volume. Measurements were made in C2F6 and CHF3 discharges in an inductively coupled plasma (GEC) research reacto r operating with power densities, pressures, gas compositions and wafer mat erials typical of those found in etch processing tools. Wafer substrates in vestigated included blanket silicon wafers and silicon wafers with varying amounts of photoresist coverage of the surface (20%, 80% and 100%). In C2F6 discharges CF3+ was consistently the dominant fluorocarbon ion present, in agreement with published cross sections for dissociative ionization. Small er concentrations of CF+, CF2+, and C2F5+, were also observed, though the d issociative ionization production of C2F5+ was a factor of 5 smaller than w ould be expected from published cross section values. The presence of photo resist, even in small amounts, was found to produce marked changes in the d ischarge composition. For example, in C2F6 discharges, concentrations of Si Fx etch products relative to concentrations of CxFy species were notably di minished and larger concentrations of water vapor were observed when resist was present. In CHF3 discharges, CF3+ and CHF2+ were found to be the main species present, along with smaller concentrations of CF2+, CF+, CHF+, CHand F+. (C) 1999 American Vacuum Society. [S0734-2101(99)13704-7].