Sifren® 46 (C4F6 or Hexafluorobutadiene) C4F6 has a GWP=0 and it is the most advanced etching gas for critical applications. Its low C/F ratio and its insaturations allow achieving the highest aspect ratios in etching.
Sifren® 46 (C4F6 or Hexafluoro-1,3-butadiene) is an unsaturated fluorocarbon with an alternating double bond. It is a colorless, odorless, toxic, flammable gas showing very high performance for plasma, ion beam, or sputter etching in semiconductor devices manufacturing with Xenon (Xe) and Argon (Ar) as carrier or dilution gas. Due to the short atmospheric lifetime (< 1day), the negligible global warming potential, and the inertness to the stratospheric ozone layer, Sifren® 46 is an environmentally compatible gas.
As long as using plasma dielectric etching it is essential to control the plasma. Chemicals such as C4F6 are able to balance etching deposition species, by which superior results are achieved compared to other gases used to produce vertical profiles.
In the C4F6 molecule the C:F ratio is high enough to control the amount of polymer on the chamber surface and wafer surface with regard to F etching radicals. More important is, that the intrinsic characteristic allows high selectivity to substrates or photo resists and wider process windows compared to e.g. C4F8 (Octafluorobutane). This behavior is particularly beneficial to address the need for sub 0.25 µm requirements.
In using Argon as carrier gas nitride selectivity can result in a decreasing function. Xenon as the other possible carrier gas has an increased selectivity. Therefore mixtures from Ar/Xe are a good compromise.