Simulation Study On Displacement Damage Effect Of Si/SiO₂ Under Neutron-γ Irradiation

The development of nuclear technology and aerospace technology has put forward higher requirements on the reliability of the electronic system in the radiation environment. Since the integrated circuit with Si as the substrate is the most important part of the electronic control system and the neutron and gamma rays are highly penetrating power in the radiation environment, it will result in a large number of damage in the Si based devices, so the study of the transportation physical mechanism inside the device has important significance.In this paper, the micro mechanism of the damage caused by the neutron and gamma ray is studied using Geant4 toolkits which is provided technical support by CERN. Through the physical model design, using the Geant4 database, different size of the SiO₂, SOI, Si detector irradiated by the single energy or continuous energy neutron or gamma ray were studied.The simulation results indicate that the total reaction cross section of neutron in Si material is derived from the elastic scattering cross section, nonelastic scattering cross section, radiation capture cross section and fission cross section. The Si PKA are mainly caused by elastic scattering and the scattering process is dominated by low energy transmission events, the number of PKA reach the maximum value in about 40 ke V, decreasing with the increasing of energy. Lots of secondary electrons are generated by gamma rays. the number and energy of the secondary electrons are very high, but γ produce no PKA directly by itself and the number of PKA is not in the same order compared with neutron produced under the same condition.For the Si detector in the centimeter scale, Si PKA recoil angle distribute in 0^π and most in 0^π/2 range, except a handful of PKA recoil angle greater than π/2 are due to the secondary collision of neutron in detector, almost all of the neutron is directly through the detector. The transport process of neutron in the nanometer scale Si/SiO₂ material was studied by the introduction of cross section bias factor, Si PKA recoil angle distribution between 0^π/2,all happens small angle scattering, and only a single interaction occurs in the neutron transportation so that the PKA is uniformly distributing.The secondary particles including γ, alpha, protons, neutrons, a small number of electrons, Al, Mg and other heavy nucleis and a large number of O PKA and a certain number of N and C atoms will be generated for SiO₂, PKA and all of these secondary particles are the primary sources of Ionization damage and displacement damage.Simulation results of the SOI structure detector radiated by neutron indicate that the number of PKA generated in the gate oxide layer is greater than that of buried oxide, all of the PKA are scattering forward and uniformly distributing in the gate oxide layer; The number of electrons in the gate oxide layer is very small, which can be considered introducing no ionizing damage; The number of PKA in the buried oxide layer are much larger than that in gate oxide for both Si and O atom, but the energy distribution is the same in the two region; The secondary charged particle recoil angle is Gauss distribution centered π/2 in 0^π range, but almost all of the various isotope recoil angle is less than 90 degrees; The energy range is much high for proton, alpha and partial heavy nucleus of the secondary particles whose maximum value reached more than 10 Me V, which is an important source of displacement damage. Whether it is PKA, isotope atom, Or charged particles,all are transported being ions in the material. Therefore, the PKA in the event of a cascade collision results in displacement damage and the electron hole pair is generated at the same time, which resulting in ionization damage...