RELATIONSHIP BETWEEN IBICC IMAGING AND SEU IN CMOS ICS

Ion-beam-induced charge-collection imaging (IBICC) has been used to st udy the SEU mechanisms of the Sandia TA670 16K-bit SRAM. Quantitative charge-collection spectra from known regions of the memory cell have b een derived with this technique. For 2.4-MeV He ions at normal inciden ce, charge collection depth for a reverse-biased p+ drain strike is es timated to be 4.8+/-0.4 mu m. Heavy-ion strikes to the reverse-biased p-well result in nearly complete collection of deposited charge to a d epth of 5.5+/-0.5 mu m. A charge amplification effect in the n-on drai n is identified and is due to either bipolar amplification or a shunt effect in the parasitic vertical npn bipolar transistor associated wit h the n+/n(-) substrate, p-well, and n+ drain. This effect is present only when the n+ drain is at OV bias. When coupled with previous SEU-i maging, these results strongly suggest that the dominant SEU mechanism in this SRAM is a heavy-ion strike to the n-on transistor drain.