Abstract: The effects of gamma irradiation on the shallow trench isolation (STI) leakage currents in a 0.18 μm technology are investigated. NMOSFETs with different gate lengths are irradiated at several dose levels. The threshold voltage shift is negligible in all of the devices due to the very thin oxide thickness. However, an increase in the off-state leakage current is observed for all of the devices. We believe that the leakage is induced by the drain-to-source leakage path along the STI sidewall, which is formed by the positive trapped charge in the STI oxide. Also, we found that the leakage is dependent on the device's gate length. The three-transistor model (one main transistor with two parasitic transistors) can provide us with a brief understanding of the dependence on gate length.

Key words: oxide trapped charge, parasitic transistor, shallow trench isolation, total ionizing dose