Evaluation of LSI Soft Errors Induced by Terrestrial Cosmic rays and Alpha Particles

It is well known that alpha particles cause soft errors in LSI. Recently, it has been found that cosmic ray neutrons also cause soft errors even at ground level [1, 2]. At present, high energy neutrons and thermal neutrons in terrestrial cosmic ray and alpha particles from radioactive decay of U, Th in mold resin are considered to be the three major causes of LSI soft errors. When a high energy neutron with energy of order of 100 MeV incidents to LSI, a spallation of Si nucleus can take place. In the spallation process, many particles such as protons, neutrons and nuclei (e.g. carbon) are generated, and they produce large number of electron-hole pairs in a short range of several µm [3]. If total electrical charge reached to a storage cell is larger than the critical charge (Qc) to upset logic, a soft error takes place. A 10B has a large cross section of thermal neutron capture. A 1.47 MeV alpha and a 0.84 MeV Li are emitted (fission) after the neutron capture, and these particles also produce electron-hole pairs. A conventional CMOS contains a large quantity of 10B in BPSG dielectric layers. Alpha particles are emitted from radioactive decay of U and Th contained in mold resin, and they also produce electron-hole pairs. We have used refined mold resin, which has lower concentration of U and Th, to reduce alpha-induced soft errors. We have performed severa