Imaging and investigation of non-uniform distributions of electrophysical properties of insulator-semiconductor structures with thin oxides

Homeotropically oriented nematic liquid crystals (NLC) have been used for visualization of different types of electrically active defects (EAD) in Si-SiO2 structures with thin (3-7 nm) oxides thermally grown on silicon. Optical images of defects revealed by the NLC method have been investigated depending on applied voltage and its polarity. Possible local properties of EAD have been studied by intentional introduction of some types of non-uniformities in Si-SiO2 structures. Selective low-energy electron (5-20 keV) irradiation by means of scanning electron microscope (SEM) has been used for this purpose. Definite similarity between images of real EAD and locally irradiated regions have been found. Possible nature of this phenomenon and peculiarities of EAD electrophysical properties are discussed. Local variations of fixed oxide charge and other electrophysical parameters have been revealed in EAD using direct measurements by mercury microprobe. In some points of EAD the local oxide conductivity have been found higher than outside defect. We have also shown that stress induced leakage currents (SILC) in the regions containing EAD are larger than in non-defect areas of Si-SiO2 structures. The presence of heavy (Fe, Cr) and alkaline metals was detected in defects by the secondary ion mass spectroscopy (SIMS). Thus, EAD revealed by the NLC method represent non-uniformities potentially dangerous for microelectronic devices with thin functional oxides.