Effect of hydrofluorocarbon structure of C₃H₂F₆ isomers on high aspect ratio etching of silicon oxide

In this study, using three isomers (1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,3,3-hexafluoropropane (HFC-236ea), 1,1,2,2,3,3-hexafluoropropane (HFC-236ca)) having the same chemical composition of C₃H₂F₆, effects of chemical branch structure of three C₃H₂F₆ isomers on the plasma characteristics and etch characteristics of high aspect ratio ACL patterned SiO₂ were investigated. During the etching of SiO₂ and amorphous carbon layer (ACL) using the three isomers mixed with oxygen, different etch characteristics and plasma characteristics were observed. In the plasmas, more CF₂ and H but, less F were related to the formation of a fluorocarbon polymer layer on the surface, while lower high mass ion species such as C₃HF₄⁺ and, C₃H₂F₅⁺ were related to the ion bombardment in the order of HFC-236fa, HFC-236ea, and HFC-236ca consequently leading to a lower SiO₂ etch rate. Therefore, when C₃H₂F₆ was used, even with the same chemical composition, the chemical branch structure of the compound affected the plasma properties and etch characteristics significantly depending on chemical branches in the compound. We believe that, for other hydrofluorocarbon compounds mixed with a critical oxygen flow rate, plasma properties and SiO₂ etch characteristics can be estimated through properties of chemical branches attached in these compounds.