Medium-energy ion scattering studies of interfaces in ultrathin oxide films.

摘要

Interfaces in thin film/substrate systems play a central role in the performance of electronic devices in nano/microelectronics. However a detailed microscopic knowledge of the structure and composition of an interface is usually not established. Medium energy ion scattering (MEIS) is a powerful technique in interface analysis by providing depth profiling with sub-nanometer resolution, MEIS been used in this thesis to study two thin film systems.;The interface between the two insulating oxides LaAlO3/SrTiO 3 has recently been found to exhibit a range of novel electronic properties, as for example a totally unexpected metallic electron mobility (two-dimensional electron gas). The origin of these novel properties is still under debate. An electronic reconstruction model, adopted by many researchers, assumes the interface to be completely abrupt and structurally perfect. MEIS has been used to systematically investigate this interface and provide the depth distributions of four metal atoms present in the overlayer/substrate system. The interface is found to be far from ideal and to exhibit substantial intermixing. A doping mechanism based on the atomic reconstruction is tentatively proposed to account for the high mobility at the interface.;The thin films of hafnium oxide and silicate have received intensive research as candidates to replace SiO2 as a gate dielectric in silicon-based electronics. Oxygen interaction with these films under high temperature annealing, a common processing treatment, is a crucial issue. An isotopic labeling technique (16O/18 O) in combination with MEIS is used to elucidate this issue. At low temperatures the incorporation involves oxygen exchange, while at higher temperatures an interfacial layer is found to form at the film/Si interface. Dependence of the oxygen incorporation on the microstructure of the film and the presence of N is also discussed.