Heavy Ion Damage in Ultra-Thin Gate Oxide SOI MOSFETs

We present the first experimental data about the response of partially (PD) and fully (FD) depleted MOSFETs manufactured in a O.l mum SOI CMOS technology to heavy ion irradiation. After exposure to just a few iodine ions, several different phenomena were present. Some effects were found in all the devices we tested with good reproducibility and depended on the ion fluence; others were present from time to time, likely depending on the exact location of the ion strike and/or on the presence of pre-existing defects. Among the first category were an increase in the gate leakage current for both PD and FD devices and a reduction in the linear kink effect which is featured only by PD samples. Concerning the sporadic effects, shifts in the threshold voltage of the main and lateral parasitic transistors and reductions in maximum transconductance were found in few devices after irradiation. We related all these phenomena to the creation of defects in the gate oxide and/or charge build-up in the lateral isolation/LDD spacers.