A comparative study of Cx(x = 4, 5, 7)F8 plasmas for dry etch processing

Abstract

In this study, the SiO2 etch characteristics of perfluorocarbon such as C4F8, C5F8, and C7F8 were investigated using inductively coupled plasmas (ICPs) to study the effect of a high C/F ratio on the etch characteristics of SiO2 for the ICP. The SiO2 rates and etch selectivities over Si3N4 and amorphous carbon layer (ACL) were measured by using the mixtures of Cx(x = 4, 5, 7)F8/Ar/O2. The higher C/F ratio of perfluorocarbon showed lower SiO2 etch rate but exhibited higher etch selectivities over Si3N4 and ACL due to the higher C2 while keeping the similar F in the plasma as observed by optical emission spectroscopy and due to the thicker fluorocarbon layer with more carbon-rich fluorocarbon on the materials surface as observed by X-ray photoelectron spectroscopy. Especially, C7F8 is environmentally benign material because it not only has a relatively low global warming potential but also can be captured easily using a capture system (a liquid state at the room temperature). Therefore, C7F8 could be applicable as one of the next generation perfluorocarbon etching materials.