Relative concentrations of reactive ions, neutral radicals, resist and substrate 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 dissociative ionization of neutral gas, and potential bias extraction of positive ions from the reactor discharge volume. Measurements were made in C2F6 and CHF3 discharges in an inductively coupled plasma (GEC) research reactor operating with power densities, pressures, gas compositions and wafer materials typical of those found in etch processing tools. Wafer substrates investigated 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. Smaller concentrations of CF+, CF2+, and C2F5+, were also observed, though the dissociative ionization production of C2F5+ was a factor of 5 smaller than would be expected from published cross section values. The presence of photoresist, even in small amounts, was found to produce marked changes in the discharge composition. For example, in C2F6 discharges, concentrations of SiFx etch products relative to concentrations of CxFy species were notably diminished 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+, CH+ and F+.