绝缘体上硅金属氧化物半导体场效应晶体管中辐射导致的寄生效应研究

基于⁶⁰Co γ射线源研究了总剂量辐射对绝缘体上硅（silicon on insulator，SOI）金属氧化物半导体场效应晶体管器件的影响.通过对比不同尺寸器件的辐射响应，分析了导致辐照后器件性能退化的不同机制.实验表明：器件的性能退化来源于辐射增强的寄生效应；浅沟槽隔离（shallow trench isolation，STI）寄生晶体管的开启导致了关态漏电流随总剂量呈指数增加，直到达到饱和；STI氧化层的陷阱电荷共享导致了窄沟道器件的阈值电压漂移，而短沟道器件的阈值电压漂移则来自于背栅阈值耦合；在同一工艺下，尺寸较小的器件对总剂量效应更敏感.探讨了背栅和体区加负偏压对总剂量效应的影响，SOI器件背栅或体区的负偏压可以在一定程度上抑制辐射增强的寄生效应，从而改善辐照后器件的电学特性.

Radiation induced parasitic effect in silicon-on-insulator metal-oxide-semiconductor field-effect transistor

In this paper, we investigate the total ionizing dose (TID) effects of silicon-on-isolator (SOI) metal-oxide-semiconductor field-effect transistors (MOSFETs) with different sizes by using ⁶⁰Co γ-ray. The SOI MOSFET contains a shallow trench isolation (STI) edge parasitic transistor and back gate parasitic transistor, in which STI oxide and buried oxide (BOX) are used as gate oxide, respectively. Although these parasitic effects are minimized by semiconductor device process, the radiation-induced trapped-charge can lead these parasitic effects to strengthen, thereby affecting the electrical characteristics of the main transistor. Since both the STI and BOX are sensitive to the TID effect, we try to distinguish their different influences on SOI devices in this work.
The experimental results show that the characteristic degradation of device originates from the radiation-enhanced parasitic effect. The turning-on of the STI parasitic transistor leads the off-state leakage current to exponentially increase with total dose increasing until the off-state leakage reaches a saturation level. The threshold voltage shift observed in the narrow channel device results from the charge sharing in the STI, while the back gate coupling is a dominant contributor to the threshold voltage shift in short channel device. These results are explained by two simple models. The experimental data are consistent with the model calculation results. We can conclude that the smaller size device is more sensitive to TID effect in the same process.
Furthermore, the influence of the negative bias at back gate and body on the radiation effect are also studied. The negative bias at back gate will partially neutralize the effect of positive trapped-charge in STI and that in BOX, thus suppressing the turning-on of STI parasitic transistor and the back gate coupling. The parasitic transistors share a common body region with the main transistor. So exerting body negative bias can increase the threshold voltage of the parasitic transistor, thereby restraining the TID effect. The experimental and simulation results show that the adjustment of the threshold voltage of parasitic transistor by body negative bias is limited due to the thin body region. The modulation of body negative bias in depletion region is more obvious in back gate parasitic transistor than in STI parasitic transistor. The weakening of parasitic conduction in the back channel is more noticeable than at STI sidewall under a body negative bias.