Etching characteristics of tungsten and tungsten compounds by energetic fluorocarbon and argon ions

Etching characteristics of tungsten (W), tungsten silicide (W3Si2), and tungsten oxide (WO3) by energetic trifluorocarbon (CF3+) and argon (Ar+) ion irradiation were examined with the use of mass-selected mono-energetic ion beams in an energy range between 500 and 4000 eV. It is found that the etching yield of W by CF3+ ion irradiation is notably higher than that by Ar+ ion irradiation when their ion energies are the same and sufficiently high, probably because of the formation of volatile tungsten fluoride (WFx) species in the case of CF3+ ion irradiation. Similarly, the etching yield of WO3 by CF3+ ion irradiation is also found to be much higher than that by Ar+ ion irradiation. In contrast, the etching yields of W3Si2 by CF3+ and Ar+ ion irradiation are found to be similar. On the other hand, the etch rates, i.e., the etched depths per unit time of W and W3Si2 by CF3+ or Ar+ ion irradiation, are found to be substantially lower than those of WO3. The results suggest that W and W3Si2 may well serve as hard mask materials for fluorocarbon-based plasma etching processes.