QUANTIFICATION OF SURFACE-FILM FORMATION EFFECTS IN FLUOROCARBON PLASMA-ETCHING OF POLYSILICON

A multibeam apparatus has been constructed which allows synthesis of the primary fluxes to a wafer surface during fluorocarbon plasma etching. These species include CF2 as a polymer forming precursor, F as the primary etchant, and Ar+ or CF(x)+ for energetic ion bombardment. The individual fluxes can be adjusted to within an order of magnitude of those encountered in typical plasma etching processes, and can be manipulated independently to ascertain the effects of radical-to-ion flux ratio on fluorocarbon film formation and etching yields. Direct sticking of CF2 radicals on undoped polysilicon films can account for suppression of silicon sputtering yields on the order of 70%, but cannot completely stop the net removal of silicon by Ar+ at energies above 150 eV. Studies of the competitive interaction between CF2 and F radicals on undoped silicon surfaces showed up to 30% suppression of Ar+/F etching yields under flux conditions representative of low pressure CF4 reactive ion etching (RIE).