Radiation Hardening of Simox Buried Oxide by Nitridation

Abstract

ABSTRACTRadiation hardening of SIMOX buried oxides by nitridation is demonstrated in this paper. Bare SIMOX oxide substrates, obtained by selective reactive ion etching of the top silicon film, were nitrided by annealing in ammonia at a high temperature. Al-Si thin film capacitors were fabricated on the SIMOX oxide and also on concurrently processed dry thermal oxides of similar thickness. Radiation hardness was tested by C-V measurements before and after the exposure to x-rays in an ARACOR x-ray source. SIMOX oxides were found to be inherently more resistant to radiation damage than the thermal oxides. Nitridation improved the radiation hardness of SIMOX oxides similarly to that of thermal oxides. Reoxidation nearly reversed the radiation hardening effect of nitridation in these thick (> 300 nm) oxides. For example, the following shifts in the flat band voltage were obtained when the capacitors were biased with ±5 V on the Al-Si dots and exposed to 100 krad (SiO2): -24 V for SIMOX oxide, -14.2 V for nitrided SIMOX oxide, and -22.8 V for reoxidized nitrided SIMOX oxide.