Plasma Atomic Layer Etching of Dielectric Materials with Low Global Warming Fluoro-Ether Isomers

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In this work, the comparative study of the plasmas of C5F10O and C4H3F7O isomers with low global warming potential (GWP) was conducted in plasma atomic layer etching (ALE) processes of dielectric materials. Plasma atomic layer etching processes for silicon oxide and silicon nitride were developed with perfluoropropyl vinyl ether (PPVE) and perfluoroisopropyl vinyl ether (PIPVE) as C5F10O isomers, and heptafluoropropyl methyl ether (HFE-347mcc3) and heptafluoroisopropyl methyl ether (HFE-347mmy) as C4H3F7O isomers. In the surface fluorination step, the dielectric surfaces were fluorinated with C5F10O and C4H3F7O isomer plasmas and the fluorinated layer was removed by ion bombardment with Ar plasma. The F1s/C1s ratio of the fluorocarbon layer in PPVE plasma analyzed by X-ray photoelectron spectroscopy (XPS) was higher when it is compared to those in PIPVE, HFE-347mcc3, and HFE-347mmy plasmas. In the removal step, ALE window was identified in 50.0 ~ 57.5 V for C5F10O isomers and 50 ~ 60 V for C4H3F7O isomers and the etch per cycle (EPC) of SiO2 was determined to be 5.4, 3.3, 2.1, and 1.8 Å/cycle for PPVE, PIPVE, HFE-347mcc3, and HFE-347mmy, respectively in the ALE window region. The EPC of SiO2 was the highest in the PPVE with a high F1s/C1s ratio of 1.57, and the lowest in the HFE-347mmy with a low F1s/C1s ratio of 1.05. The global warming effect of the exhaust gases was evaluated by carbon dioxide equivalent values determined from the concentration of the exhaust gases. The carbon dioxide equivalent was reduced up to 90%, compared to that of C4F8 plasma. The carbon dioxide equivalent of C4H3F7O isomer plasmas was the lower than that of C5F10O isomer plasmas due to the generation of HF and CO, having much lower GWPs as major reaction products.