In situ dry cleaning of Si wafer using OF₂/NH₃ remote plasma with low global warming potential

Dry cleaning technology is an essential technique that can be applied to remove native oxide and various contaminants during the semiconductor manufacturing for nanoscale electronic devices. In this study, the in situ dry cleaning of silicon dioxide (SiO₂) with low global warming potential (GWP) gas mixtures has been investigated by sequential process steps composed of the reaction of SiO₂ surface by oxygen difluoride (OF₂) (GWP: <1)/ammonia (NH₃) remote plasma and the removal of the reacted compound layer by lamp heating. By using the optimized OF₂/NH₃ (2:1) mixture for the surface reaction followed by the lamp heating at 200 °C to remove the reacted compound layer, a high-SiO₂ cleaning rate and etch selectivity over silicon nitride (>30:1) could be obtained due to the formation of the highest HF concentration on the SiO₂ surface at the OF₂/NH₃ (2:1) gas ratio. The compound layer formed during the reaction was (NH₄)₂SiF₆ observed for a previously investigated NF₃ (GWP: 17 200)/NH₃ plasma, but the dry SiO₂ cleaning rate and the etch selectivity over Si₃N₄ obtained by the OF₂/NH₃ plasma were higher than those by the optimized NF₃/NH₃ plasma. The effects of OF₂/NH₃ mixture dry cleaning on the electrical characteristics of metal-oxide-semiconductor (MOS) devices fabricated on the nano-scale trench patterned Si substrate with high aspect ratio were studied and compared with conventional wet and NF₃/NH₃ mixture dry cleaning-based devices. Compared with other cleaning methods, OF₂/NH₃ dry-cleaning shows the improved and reliable electrical characteristics such as sharper capacitance-voltage behavior, lower hysteresis, less interface trap charge and smaller contact resistivity. Therefore, it is believed that the in situ sequential dry SiO₂ cleaning with the OF₂/NH₃ remote plasma can be applied as an essential cleaning method with extremely low GWP for fabricating next generation nano-scale devices.