Research On The Mechanism Of Total Dose Irradiation Based On 22nm FDSOI Device

With the rapid development of the semiconductor industry,ordinary bulk-Si MOS devices can no longer meet the needs of the industry.FDSOI devices have become an alternative to bulk-Si devices because of their superior gate control capability and lower leakage current.Because of its full dielectric isolation structure,it has outstanding advantages in resisting single event effect and dose rate effects,and has broad application prospects in the aerospace and military fields.However,it is also sensitive to the total dose effect due to the full dielectric isolation structure,which makes it more difficult to analyze the radiation degradation.At present,the CMOS fabrication process has reached the ultra-deep sub-micron level,and the gradually thinning gate oxide has been insensitive to total dose radiation,but the BOX and STI structures that have not been reduced with the feature size of the device are still sensitive to the total dose effect.This paper mainly conducts a simulation study on the FDSOI NMOS device at the 22 nm process node,and analyzes the damage mechanism of the BOX layer and the STI area leading to the total dose effect of the device,the influence of the device structure parameters on the total dose effect,the non-ideal effects of radiation enhancement,and two kind of reinforcement method.First,a device model for simulation is constructed,and the characteristic parameters are compared and corrected with the tape-out device in the reference paper to ensure the accuracy of the device model.The damage mechanism of the BOX layer and the STI zone leading to the total dose effect of the device was simulated.The radiation charge generation rate and the trap trapped charge distribution under three common irradiation biases were analyzed,and it is found that for the BOX layer,the worst irradiation bias is the TG state;and for the STI area,the worst irradiation bias is the ON state;considering the BOX layer and the STI area at the same time,the worst irradiation bias is the TG state.A comparative analysis of the three cases is carried out,and it is found that the STI region has the greatest impact on the subthreshold region of the device.Then,the device structure parameters that are sensitive to the total dose effect are extracted through the charge sharing model,and it is found that the increase in the aspect ratio of the device can reduce the sidewall parasitic effect caused by STI,thereby reducing the impact of the total dose effect.In the actual fabrication process of the device,the STI sidewall spacers are not vertical.The non-vertical sidewalls spacers cause changes in the size of parasitic transistors formed by the BOX layer and STI region,and the area of the parasitic channel that can conduct electricity increases,which in turn leads to poor device performance.The simulation results show that the steeper the sidewall of the STI,,the better the device's resistance to total dose radiation.The influence of the thickness of the BOX layer on the total dose effect is studied,and it is found that reducing the thickness of the BOX layer can improve the device's resistance to total dose radiation.Then the non-ideal effects of radiation enhancement are analyzed,and it is found that the positive trapped charge introduced by radiation will increase the surface roughness scattering of the device,reduce the mobility of the device,and then cause the degradation of the device transconductance,and these phenomena will follow The increase in radiation dose has become more pronounced.At the same time,it is found that the positive trapped charge introduced by irradiation will change the electric field in the channel,resulting in a decrease in the source-drain barrier,a decrease in the gate control capability,and an increase in the leakage current.The drain induced barrier lowering effect becomes more obvious with the increase of radiation dose.The total dose irradiation will also make the channel length modulation effect more obvious,and the unsaturated leakage current characteristics of the parasitic transistor in the saturation region will also be superimposed on the main transistor of the device,causing the overall output characteristic curve of the device to warp in the saturation region.Finally,the structural reinforcement method of introducing a sacrificial layer into the BOX layer is studied.The simulation results show that the structure of the reinforced device has good radiation resistance,and the total dose effect of the device can be further improved by thinning the top Si O₂ in the buried layer;The doping reinforcement method of adding P+doped regions to the edge of the source and drain is studied.The increased P+doped regions cut off the current leakage path generated by the STI sidewall under the irradiation,showing good resistance to radiation,but at the same time reducing the device performance,simulation shows that a narrower P+doped region can play a good reinforcement effect.