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

Abstract

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 degrees 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)(2)SiF6 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.