Study on polymeric neutral species in high-density fluorocarbon plasmas

Production and extinction processes of polymeric neutral species (CmFn;m gr eater than or equal to 2) in electron cyclotron resonance C4F8 and CF4 plas mas have been studied by using a quadrupole mass spectrometer (QMS) employi ng low-energy electron attachment technique. This technique allows the dete ction of electronegative CmFn species as negative ions by scanning the atta ching electron energy in the QMS typically in the range of 0-10 eV. in addi tion to the most abundant F- and CF3- signals resulting from dissociative a ttachment to various fluorocarbon species, pronounced attachment resonances of negative ions corresponding to the series of CmF2m+/-1- such as C3F7- C 4F9- and C5F9- were primarily observed especially at low microwave powers a nd high pressures. The C4F8 plasma contained a large amount of polymeric sp ecies and a high fraction of reactive F-stripped species as compared to the CF4 plasma, providing evidence of a high potential of gas phase and surfac e polymerization in a low F/C ratio plasma. The amount and composition of p olymeric species were examined by varying gas residence time and diluted hy drogen or argon concentration. At 20 mTorr, the overall amount of polymeric species was suppressed by enhanced gas flow with decreasing residence time , while a fraction of F-stripped species was increased. The amount of polym eric species was also suppressed with increasing diluted hydrogen, and the different behavior in the two plasmas was interpreted as the result of inte ractions between H atoms and polymeric species. The results provide insight s into the kinetics and chemical activity of polymeric species in a high-de nsity plasma as a practical etching source. (C) 2000 American Vacuum Societ y. [S0734-2101(00)04201-9].