Characteristics of high aspect ratio SiO2 etching using C4H2F6 isomers

The present work used three C4H2F6 isomers (hexafluoroisobutylene [C4H2F6 - iso], (Z)-1,1,1,4,4,4-hexafluoro-2-butene [C4H2F6 - z], and cis-1,1,2,2,3,4-hexafluorocyclobutane [C4H2F6 - cyclo]) having the same chemical composition but different molecular structures, different components, and different global warming potentials (GWPs) to investigate the characteristics of plasmas and etch characteristics of SiO2 masked with an amorphous carbon layer (ACL). The different structures in the C4H2F6 isomers showed different fluorocarbon-based species (CF, CHF, CF2, CHF2, and CF3) and atomic species (H and F) in the plasma, therefore resulting in different characteristics of remaining fluorocarbon polymer on the sample surfaces after the etching and dielectric etch characteristics. Cyclic structured C4H2F6 showed a lower dissociation of molecules compared to the linear molecular structured C4H2F6, thus leading to differences in the concentration and species of high mass ions in the plasma and different etch profiles. These differences in plasma and etching characteristics among C4H2F6 isomers decreased in response to an increase in oxygen flow rate, which was attributed to a higher dissociation of isomer molecules by oxygen. Therefore, by controlling the oxygen flow rate, and using a low F/C ratio of C4H2F6 isomers, extremely selective SiO2 etching over the ACL mask can be applied to next-generation HARC etching.