Low Global Warming Potential Alternative Gases for Plasma Chamber Cleaning

Etch characteristics of SiO2 and Si3N4 using gas mixtures of C3F6O (HFA (Hexafluoroacetone) and HFPO (Hexafluoropropylene oxide))/O-2 were investigated as potential cleaning gas mixtures for SiO2/Si3N4 chemical vapor deposition chamber and their etch rates were compared with those using NF3. The etch rates using 100% HFA and 100% HFPO were significantly lower than those etched with NF3. However, when oxygen gas was mixed with HFA and HFPO while keeping total gas flow rate same, the etch rates of SiO2 and Si3N4 were increased with the increase of oxygen flow rate and were reached to 53% for Si3N4 etching and 46% for SiO2 etching compared to the etch rates using NF3 at 70% of oxygen percentage and the further increase of oxygen percentage decreased the etch rates. The highest etch rates at 70% of oxygen percentage were related to the highest atomic F concentration and the highest F/CFx ratio in the plasma due to the release of F from C3F6O by oxygen and also were related to the removal of a fluorocarbon polymer layer formed on the SiO2 and Si3N4 surfaces at higher oxygen gas percentages. At the oxygen percentage higher than 70%, the etch rates were decreased because the atomic F concentration was decreased due to the lower C3F6O gas flow rate for the same total flow rate. Even though the etch rates with HFA/O-2 and HFPO/O-2 are about half of those with NF3, due to the significantly lower global warming potential (GWP) of < 100 compared to 16,100 of NF3, it is believed that, HFA/O-2 and HFPO/O-2 could be utilized as potential environmentally benign chamber cleaning gases.