A framework for understanding fast-neutron induced defects in SiO2 MOS structures

Abstract

Neutron radiation damage in solids results from nuclear collisions and reactions that produce energetic recoil atoms. The recoiling atoms slow down in the host material through nuclear and electronic collisions. During a nuclear collision, energy is transferred to translatory motion of another atom, whereas during an electronic collision, energy is transferred to atomic electrons, leading to electronic excitation or ionization. Nuclear collisions may result in displacing additional host atoms from their lattice sites if the energy received by the host atom is greater than the displacement threshold energy. As neutrons pass through the thin thermally grown gate oxide of a MOSFET device, they produce both silicon and oxygen primary knock-on atoms (PKAs). These PKAs can produce significant displacement damage regions in the bulk oxide which become potential hole traps or mobile ionic charge traps similar to the condition at the SiO2/Si interface. It is also suspected that these PKAs may deposit part of their energies into plasmons, which will eventually decay to electron-hole pairs causing charge buildup at the interface, when the MOSFET device is in operation. Since the gate oxide region is susceptible to electronic effects, it is important to know the amount of damage from individual neutron interactions in the oxide layer. A key to a theoretical study is provided in this paper. Analytical and direct-simulation estimates are made of the neutron damage.