Mechanisms of positive charge generation in buried oxide of UNIBOND and SIMOX SOI structures during high-field electron injection

Mechanisms of the generated positive charge and the charge trapping during the high-field electron injection at constant voltage regime in buried oxide (BOX) of silicon-on-insulator (SOI) structures fabricated by UNIBOND and single implanted separation by implanted oxygen (SIMOX) technologies are studied by capacitance–voltage characteristics. It is found, that considerable positive charge is accumulated near the buried oxide/substrate interface independently from direction of the injection (from film or from silicon substrate) for both kinds of structures. Comparison of the theory and experimental data allows to suggest that in the case of the UNIBOND buried oxide a positive charge is generated by two mechanisms—anode hole injection and band-to-band impact ionization. In the case of the SIMOX SOI material at the high-field electron injection in the buried oxide the anode hole injection with defect creation at precursor sites in the strained structure of oxide network is supposed to appear. It is shown, that the positive charge in the UNIBOND BOX can be completely annealed at a temperature of 400 °C while in the SIMOX BOX it is much more stable and the annealing temperature increases with the electron injection electric field rising