Technical University of Clausthal physicists have made progress in characterising the atomic structure of silicon/silicon dioxide interfaces (Physical Review Letters, Volume 93, No.9, on-line August 27, 2004).
Technical University of Clausthal physicists have made progress in characterising the atomic structure of silicon/silicon dioxide interfaces (Physical Review Letters, Volume 93, No.9, on-line August 27, 2004). Using a nonlinear optical method, Dr Stefan Bergfeld, Bjoern Braunschweig and Professor Winfried Daum studied the change in bond structure of interfacial atoms during the oxidation of a (111)-oriented silicon surface. The scientists also observed the changes in bonding states after thermal oxidation. The technique used the frequency doubling of laser light converted by the interfacial atoms to near ultraviolet. This allows non-destructive characterisation of the oxidation process under real conditions and also provides very high interfacial sensitivity, in comparison with other optical methods.
The Si(111)-SiO2 interface is a prime example of an abrupt transition from a perfect crystal structure to an amorphous oxide. Unfortunately it is the Si(100) surface that is used in the majority of semiconductor production processes. Indeed, a few years ago the team attempted to apply the technique to the (100) but found it difficult to interpret the results. However, by studying the surface of the (111)-terminated silicon crystal, Daum reports that the team has clarified the interpretation of the raw data from the method and the nature of the oxidation process. This because the (111) surface possesses a structure consisting of bi-layers, in which changes in the bond structure resulting from oxidation can be observed especially well. The team now plans to return to the (100) surface structure in the next few weeks.
