Research on total-dose hardening for H-gate PD NMOSFET/SIMOX by ion implanting into buried oxide

Abstract

In this work, we investigate the back-gate I-V characteristics for two kinds of NMOSFET/ SIMOX transistors with H gate structure fabricated on two different SOI wafers. A transistors are made on the wafer implanted with Si+ and then annealed in N2, and B transistors are made on the wafer without implantation and annealing. It is demonstrated experimentally that A transistors have much less back-gate threshold voltage shift ΔVth than B transistors under X-ray total dose irradiation. Subthreshold charge separation technique is employed to estimate the build-up of oxide charge and interface traps during irradiation, showing that the reduced ΔVth for A transistors is mainly due to its less build-up of oxide charge than B transistors. Photoluminescence (PL) research indicates that Si implantation results in the formation of silicon nanocrystalline (nanocluster) whose size increases with the implant dose. This structure can trap electrons to compensate the positive charge build-up in the buried oxide during irradiation, and thus reduce the threshold voltage negative shift.