Angular dependence of proton single event multiple-cell upsets in nanometer SRAM

Abstract

Single event multiple-cell upsets (MCU) increase sharply as the feature size of semiconductor devices shrinks. MCU poses a large challenge on present radiation hardening technology and modeling test technique. Experimental study of the influence of proton incidence angle on single event multiple-cell upsets in 90 nm static random access memory (SRAM) for middle and high energy proton is carried out. The result shows that MCU percentage and multiplicity increase with increasing proton energy, and the MCU topological pattern presents a certain track-orientation characteristic along the trajectories of the incidence ion when the incidence proton is tilted along the X-direction or Y-direction. Single event upset (SEU) cross section has no evident angular dependence. There is some difference in proton MCU cross section between normal incidence and tilt angle incidence only for 30 MeV proton. Angular effect of proton MCU is associated with proton energy. Due to the lower efficiency of Monte-Carlo method in calculating proton MCU, a fast calculation method for cross section, which aims at single event MCU induced by proton nuclear reaction, is adopted. The binary cascade model in Geant4 toolkit serves as event generators in middle on high proton nuclear reaction. In terms of double differential scattering cross section of secondary particle from proton-material spallation reaction, proton MCU cross section is calculated through integration over the entire space of memory cells array. Based on the distribution of secondary particles, those spallation products with the highest linear energy transfer (LET) and longest range are revealed to emit preferentially in the forward direction, which is the root cause why the angular effect of proton-induced MCU exists. The angular dependence of single event MCU in nanometer SRAM depends strongly on proton energy and critical charge. The higher the proton energy is, the wider the angular distribution of secondary particle is, the greater the energy and LET value of the lateral scattered secondary particle is; and so the angular enhancement effect in MCU cross section for lower energy protons is greater than the higher energy protons. MCU cross section is more isotropic with the increase of the proton energy. Angular effect in MCU cross section becomes stronger with the increase of the critical charge for the same energy proton.