Response of SIMOX and Unibond buried oxides: trapping and detrapping properties

X-ray induced charge trapping and detrapping properties are investigated in SIMOX (separation by implantation of oxygen) and Unibond buried oxides. Irradiation are performed using an Aracor (model 4100) 10 keV X-ray source, under different front and back-gate bias conditions. The back-gate parasitic conduction is recorded, and the Vit and Vot components were extracted from the subthreshold slope by using the standard method of Mc Whorter and Windkur. 4 geometries of transistors are studied in order to check the consistency of the results and no anomalous effect was noticed. A quick comparison of the ΔVot anneal data presented shows that depending on the amount of radiation dose, the variation of the net oxide trapped charge can be very different. At low dose, here 10 krad(SiO2), the evolution of ΔVot is almost not observable until 175 Celsius degrees, whereas at higher doses (from 50 krad(SiO2) on and also for 20 Mrad(SiO2)) the decrease of the net trapped charge is immediate. The authors discuss different possible explanations to this behavior. The data obtained show that even if irradiation results (concerning trapping properties) might look very similar, some differences are observed on the post-irradiation behavior of the 2 materials. (A.C.)