Effect of O2(CO2)/C4F8O gas combinations on global warming gas emission in silicon nitride PECVD plasma cleaning

In this study, O2/C4F8O and CO2/C4F8O have been used as the chemicals for plasma-enhanced chemical vapor deposition (PECVD) chamber-cleaning of silicon nitride, and the effects of gas mixture and operational pressure on the silicon-nitride cleaning rate and emission properties, such as emission species, destruction and removal efficiencies (DREs), and million metric tons of carbon equivalent (MMTCE), have been investigated. O2/C4F8O generally showed a higher silicon-nitride cleaning rate compared to CO2/C4F8O, possibly due to the removal of fluorine by carbon in CO2. The highest silicon-nitride cleaning rate obtained with O2/C4F8O was approximately 600 nm/min for 80% O2/20% C4F8O at 66.7 Pa (500 mtorr), 40 sccm, 150 W of 13.56-MHz RF power, and without substrate heating. Emission species, such as CF4, COF2 and CO2, were observed through the exhaust line during silicon nitride cleaning, in addition to the undestructed remaining feed gases. The quantities of these emission species were higher than that of C4F8O fed through the cleaning chamber. With 80% O2/20% C4F8O, the highest DREs and the lowest MMTCE obtained were 92% and 3×10−10, respectively. In the case of CO2/C4F8O, silicon nitride cleaning rates were lower, the DRE was lower and MMTCEs were higher than those of O2/C4F8O.