利用Geant4模拟研究中子在半导体中引发的单粒子翻转效应

Neutron induced single event upset in CMOS simulated with Geant4

静态随机存储器在反应堆中子辐射环境中会发生单粒子翻转(Single event upset,SEU)。钨和铜等重金属作为局部互联,在半导体中已得到广泛应用,这些重金属对中子在半导体中的单粒子翻转截面会产生影响。不同条件下单粒子翻转截面与临界能量的关系可作为器件设计和使用时的参考,利用Geant4对特定中子能谱在CMOS(Complementary metal oxide semiconductor)器件中的能量沉积进行模拟,给出特定能谱下翻转截面σ与临界能量Ec的关系:σ=exp[-18.7×Ec-32.3],其中能量单位为Me V,截面单位为cm2。并且模拟了1-14 Me V的单能中子在含有互联金属钨及不含钨的CMOS中的沉积能量及单粒子翻转截面,得出在1-14 Me V内单粒子翻转截面随中子能量而增大,且钨的存在会增加α粒子的产额,从而增大了1-3 Me V中子的单粒子翻转截面,而对4-14 Me V中子基本不会产生影响。

Background： Reactor neutron can induce single event upset （SEU） in Static Random Access Memory （SRAMs）. Local metal intereonnection is widely used in modern complementary metal oxide semiconductor （CMOS） technology. The most frequently used local materials are some heavy metals, such as tungsten （W） or copper （Cu）. These metals could affect the neutron induced SEU in CMOS. Purpose： The relationship between SEU cross section and critical energy （Ec） can be referred by SEU experiments with reactors. Methods： The SEU cross sections with different Ec of a SRAM are simulated and calculated using Geant4 with a reactor neutron spectrum, and SEU induced by 1-14 MeV neutrons are also simulated in structures with and without a tungsten layer. Results： The relationship between SEU cross section a （in unit： cm^2） and Ec （in unit： MeV） is σ=exp[-18.7xEc-32.3]. In the structure with a tungsten layer, SEU cross sections induced by 1-3 MeV neutrons are increased because a few ct particles are created. Conclusion： To reduce neutron SEU cross section, the critical energy of CMOS should be increased as high as possible, and usage of tungsten should be avoided.