Characteristics of SiO₂ Etching by Capacitively Coupled Plasma with Different Fluorocarbon Liquids (C₇F₁₄, C₇F₈) and Fluorocarbon Gas (C₄F₈)

Abstract

Fluorocarbon (C 7 F 14 , C 7 F 8 ) plasmas are investigated to verify their etching characteristics as an alternative etchant of SiO 2 etch process because C 7 F 8 and C 7 F 14 precursors are expected to have low Global warming potentials. Comparing the etch results of C 4 F 8 , C 7 F 14 , and C 7 F 8 plasmas, C 7 F 8 provides the highest selectivity for etching SiO 2 at a moderate etching rate of the three fluorocarbons. C 4 F 8 and C 7 F 14 plasmas show similar magnitudes of selectivity at the same O 2 injection. O 2 addition is used to control densities of carbon species and optimize etching conditions. From comparison of the species existing in the C 4 F 8 , C 7 F 14 , and C 7 F 8 plasmas by the electron-emitting source, CF radicals and carbon atoms are important in determining the remarkable selectivity of C 7 F 8 plasma. This understanding is verified using X-ray photoelectron spectroscopy analysis.