Research On The New Structure And Model Of Single-event Radiation Hardened Power MOSFET Devices

There are a lot of X-rays,gamma rays,neutrons,heavy particles and so on in space.Spacecraft will be radiated by such rays and particles in space operation,which will cause disturbance of spacecraft electronic system,even lead to electronic system failure,seriously affecting the safe operation of spacecraft in orbit.Hence,there are technical bottlenecks in SEB and SEGR hardening solutions of power VDMOS devices used in aerospace field.In this thesis,the single-event radiation-hardening technologies of power VDMOS devices are systematically discussed,based on a deep analysis of the single-event radiation effect and physical process of power VDMOS devices.Two novel VDMOS structures,DSPSOI_MOS and DBL_MOS,are proposed for improving single event radiation hardening capability.The design,tape out and the radiation test verification for the devices are completed.Taking DBL_MOS device as a typical example,this thesis introduces the design and process details of the device sample,and the single event radiation test results of SFC+SSC cyclotron in Institute of Modern Physics,Chinese Academy of Sciences are analyzed and discussed.The testing results show that the single event radiation safe operating area of the device is increased by 100%,from 60V to 120V,under the condition of ¹⁸¹Ta ion with 1400.8MeV energy,83.3?m range in silicon and LET value of 81.35MeV.cm²/mg vertically radiating.Some views on radiation effect,evaluation model,hardening technology and radiation test of power VDMOS devices are included in this thesis.The main research contents and innovative achievements are as follows:1.Single event radiation effects of power VDMOS devices have been studied for more than 30 years.Publications about the single event radiation effects of power VDMOS devices include gate oxide-related SEGR effects and parasitic bipolar junction related SEB effects,because of the inherent gate oxide and parasitic bipolar junction structure in a VDMOS.However,there are few research reports describing the correlation between SEGR and SEB.After deep analysis of the SEB and SEGR effects,the author figured out a SEB-induced SEGR effect in power VDMOS.When heavy ions incident from the source or channel region of VDMOS devices,SEB occurs first and then SEGR occurs.This new effect has been verified by TCAD simulation and single event radiation test experiments.Features of the SEB-induced SEGR effect are as follows:?1?The SEB-induced SEGR effect just can be triggered when heavy particles incident from the source or channel region of power VDMOS.?2?The power VDMOS will not be destroyed by SEB effect,If a intrinsic breakdown voltage of gate oxide is high enough at high temperature.?3?The SEB effect will result in a high current density in the local region near the gate oxide layer of the device,which will lead to a sharp increase in the local lattice temperature and a decrease in the intrinsic breakdown of gate oxide layer.Thus the SEGR effect will be triggered.Then an SEB induced SEGR effects occurs.2.Based on the analysis of the single event effect of power VDMOS devices and in-depth understanding of the interaction between heavy particles and materials,the process of single event radiation of VDMOS devices can be divided into three stages.The first one is energy deposition,the second one is atomic ionization and the third one is charge collection.Corresponding device-level reinforcement methods are proposed for three stages of single particle radiation.For the first stage,a shielding technology,that is covering a heavy metal?Au,Cu,Ni,etc.?layer on the top of the chip,is proposed.The heavy metal layer is used to attenuate or shield the energy of heavy particles,which is lowered when the heavy particles reach the silicon surface.For the second stage,a hardening technique,which is to insert some fast recombination centers on the incident tracks of heavy particles in the device body,so as to reduce the number of new electrons and holes produced by ionization,is proposed.For the third stage,an enhancement technology,which is to improve the intrinsic breakdown of gate oxide layer and the trigger threshold of parasitic transistors in power VDMOS devices,is proposed.Three kinds of reinforcement technologies correspond to the three stages of single event radiation process,respectively.They can be combined to construct different power VDMOS in different hardening schemes according to different needs.A single event radiation hardened power VDMOS with Ni metal shielding layer and Pt recombination center had been designed and fabricated.Testing results verified the feasibility of the shielding technology and the recombination technique for improving single particle radiation hardening capability of power VDMOS.3.According to the proposed methods of single event radiation hardening technology for power VDMOS devices,two new VDMOS structures with double stagger partial SOI or double buried layer are proposed,by using the carrier lifetime modulation effect of Si-SiO2interface and heavy doped buried layer.The devices have been numerically simulated.The single event radiation safe operating area of the VDMOS with double stagger partial SOI is improved by 50%.The single event radiation safe operating area of the VDMOS with dual buried layer is improved by 178%.Using ¹⁸¹Ta ions with 1400.8MeV energy,83.3?m range in silicon and LET value of 81.35MeV.cm²/mg to incident the DBL_MOS device vertically,the safe operating area of the device has been increased from 60V to 120V,by 100%.4.Several interesting phenomena have been found during the verification of single event radiation test for power VDMOS devices.But the detailed physical mechanism of these phenomena is not fully clear yet.Further research work is needed.?1?During the non-destructive single-event experiment,it was found that the leakage current of the power VDMOS increased gradually with the increase of total radiation fluence.And it could not recover immediately after the radiation stopped.At this time,total ionizing dose-like radiation effect is induced by single-event radiation.?2?During the total dose measurement of ionizing radiation for an N-type VDMOS,it is found that whether the threshold voltage of the device rebounds or not depends on the bias voltage.In the worst drain-source bias test,there is obvious threshold voltage rebound phenomenon.While in the worst gate-source bias test,no rebound phenomenon is observed.