Low-global warming potential fluoroether compounds for plasma etching of SiO₂ and Si₃N₄ layers

In this study, the authors investigated the applicability of fluoroether compounds such as CF₃CF₂CF₂OCH₃ (HFE-347mcc3), (CF₃)₂CFOCH₃ (HFE-347mmy), and CF₃CF₂CF₂OCF=CF₂ (PPVE) with low lifetimes and global warming potentials for the plasma etching of SiO₂ and Si₃N₄ layers in inductively coupled plasma. The isomeric effects of HFE-347mcc3 (with the methoxy group at the end) and HFE-347mmy (with the methoxy group at the center) were also compared. PPVE produced larger amounts of low-mass fluorocarbons (CF, CF₂, CF₃) than C₄F₈ and hence showed a higher etch rate than C₄F₈ for all the substrates. The HFE-347mcc3 and HFE-347mmy plasmas consisted of large amounts of H and HF. Hence, their Si₃N₄ etch rates were higher than that of C₄F₈. The etch rate of HFE-347mmy was slightly higher than that of HFE-347mcc3 for all the substrates. The density of C₄F₈ was slightly higher than that of fluoroethers. However, the difference was not significant under the experimental conditions used in this study. The million metric ton carbon equivalents (MMTCEs) of all the etchants were calculated from the concentration of the exhaust gases produced by them during etching. The MMTCEs of PPVE and HFE-347mcc3/HFE-347mmy were 49% and 90%, respectively, lower than that of C₄F₈. The fluoroether compounds used in this study demonstrated a significantly reduced global warming effect as compared to C₄F₈ and hence can be used as potential etchants.