Scanning Microscopy


A nuclear microprobe with a minimum beam-spot diameter of less than 100 nm, intended for application to IC (integrated circuit) process inspection, has been designed and installed at Osaka University. An ultra high-vacuum sample-chamber with a three-axis goniometer stage and a toroidal electrostatic analyzer for medium energy ion scattering (MEIS) was combined with a short acceleration column for a focused ion beam. A liquid metal ion source (LMIS) for light metal ions such as Li+ or Be+ was mounted on the short column. A minimum beam spot-size of about 80 nm with a current of 30 pA was obtained for 400 keV Be++ LMIS. An energy resolution of 4 x 10-3 (ΔE/E) for the toroidal analyzer gives rise to atomic resolution in RBS spectra for Si and GaAs. This system seems feasible for atomic-level in-depth analysis of localized surfaces and crystalline/disorder structures. The design concept and simulated focusing characteristics using beryllium and lithium liquid metal ion sources were compared with those of conventional microprobes. The feasibility of this microprobe to localized analysis of future IC process steps with a minimum feature size of less than a quarter micrometer was discussed.

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