BLOCKING OF THERMALLY-INDUCED INTERFACE DEGRADATION IN (111)SI SIO2 BY HE/

The interface degradation induced in (lll) Si/SiO2 by postoxidation an nealing in vacuum, previously identified by electron spin resonance as intense creation of interfacial Si dangling bond defects (p(b)s: (Si3 Si)-Si-= . ) from approximate to 640 degrees C on, is found to be rem arkably suppressed when annealing in He ambient. On the time scale of approximate to 1 h, He firmly blocks the degradation up to approximate to 800 degrees C, from which temperature on Pr, creation gradually ri ses, though much suppressed as compared to the vacuum case. At approxi mate to 1140 degrees C, the Ph density drops abruptly to a value (appr oximate to 1.7 x 10(12 )cm(-2)) about one-third that of the as-oxidize d state density, indicating an electrically much improved interface. T he transition results from the known thermal cooperative restructuring of the SiO2 layer, completed at approximate to 1140 degrees C. The da ta support the degradation model based on interfacial SiO(g) release, where He is seen as rapidly occupying the SiO accessible sites in the oxide thus inhibiting the degradation mechanism through impeding SiO r emoval-a prerequisite for the degradation to occur.