Surface loss coefficients of CFx and F radicals on stainless steel

The surface loss coefficients of CFx (x = 1 - 3) and F radicals have been m easured on the stainless steel walls of the differential pumping systems of a plasma reactor. This measurement is made by comparing the beam to backgr ound signal ratio of the radicals measured by appearance potential mass spe ctrometry. The surface loss of the radicals in the differential pumping sta ges of the vacuum system, in addition to the pumping of the species due to the vacuum Dump, increases the beam to background signal ratio of the radic al species. The measured loss coefficients are found to be lower than those reported on surfaces that have been exposed to fluorocarbon plasmas. This suggests that the loss coefficients of the species are dependent on the sur face coverage of the radicals (CFx and F), which are lower on the walls in the differential pumping system. The measured loss coefficients in the diff erential pumping system are an order of magnitude lower than the loss coeff icients measured in the afterglow of plasma chambers reported in the litera ture. We suggest the difference in the loss coefficients of radicals in the plasma chamber and those measured in this work are due to the differences in surface coverage in the two cases. (C) 2000 American Vacuum Society. [S0 734-2101(00)00806-X].