THIN-GATE SIO2-FILMS FORMED BY INSITU MULTIPLE RAPID THERMAL-PROCESSING

A reliable method of forming verv thin SiO2 films (< 10 nm) has been developed by rapid thermal processing (RTP) in which in situ multiple RTP sequences have been employed. Sub-10-nm-thick SiO2 films formed by single-step RTP oxidation (RTO) are superior to conventional furnace-grown SiO2 on the SiO2/Si interface characteristics, dielectric strength, and time-dependent dielectric-breakdown (TDDB) characteristics. Moreover, it has been confirmed that the reliability of SiO2 film can be improved by pre-oxidation RTP cleaning (RTC) operated at 700-900-degrees-C for 20-60 s in a 1%HCl/Ar or H-2 ambient. To make further improvements in the long-term reliability, we have introduced a new nitridation technology in which the RTO process has been followed bv in situ RTP oxynitridation (RTON) in an nitrous oxide (N2O) ambient. By this multiple process, we have achieved highly reliable nitrided SiO2 films. This N2O-nitrided SiO2 film, which includes about 5 at % nitrogen at the SiO2/Si interface, has shown a larger charge-to-breakdown value (> 30 C/cm2), a smaller change in the interface trap density, and a lower density of charge trapping in high-field stressing (> 8 MV/cm). From these results, we consider that in situ multiple RTP sequences should be a kev technology for obtaining high-quality thin-gate SiO2 films.