Ion Impact Detection and Micromapping With a SDRAM for IEEM Diagnostics and Applications

Ion electron emission microscopy (IEEM) can provide an alternative approach to microbeams for micrometric characterization of the sensitivity map to single event effects (SEE) of an electronic device. In IEEM technique, a broad (not focused) ion beam is sent onto the device under test (DUT). Secondary electrons emitted by the target surface during each ion impact are collected and focused by a system of electrostatic lenses and finally imaged by a high-rate and high-resolution position detector. We will report on the IEEM working at the SIRAD irradiation facility located at the 15 MV Tandem of INFN Legnaro National Laboratories. To estimate the IEEM resolution, a SDRAM is a good candidate to be used as a reference target, thanks to the micrometric feature size of the array of memory cells and the precise knowledge of their physical locations. Since an electronic device is not a good secondary electrons emitter, to ensure a copious and uniform emission of secondary electrons from the DUT, a very thin (100 nm) self-standing silicon nitride (Si₃N₄) membrane with a Au deposition (40 nm) is mounted on the top of the SDRAM. The Au/Si₃N₄ membrane and the underlying SDRAM are irradiated with a heavy ion beam. The physical map of ion impacts detected by the SDRAM is then compared with the one reconstructed by the IEEM in the same 500 ms time interval.