DYNAMIC OBSERVATIONS OF INTERFACE MOTION DURING THE OXIDATION OF SILICON

We describe real time observations of the behaviour of the silicon-oxide interface during oxidation in situ in an ultrahigh vacuum transmission electron microscope. We have formed clean, flat Si(111) surfaces by heating under UHV and allowed oxidation or oxygen etching to proceed in the microscope. We have examined the kinetics of both the oxidation and etching reactions using an imaging technique based on the use of forbidden reflections in silicon. We find that oxidation to form SiO2 occurs by the reaction of discrete monolayers with no flow of surface steps. This is in dramatic contrast to oxygen etching, during which the volatile oxide SiO evaporates preferentially from step edges.