Scanning Electron Microscopy


The limitations on secondary ion micro-analytical performance imposed by ionization probabilities, mass spectrometer transmission, requirements for standards and sputtering artifacts have been investigated. The sensitivity of a modern magnetic mass spectrometer for sputtered B+ from oxidized Si is ~ 10-2 ions detected/atom sputtered. For this sensitivity, it is shown that ion microscopy of a part-per-million impurity is limited in lateral resolution to ~ 1 μm. For a 1% impurity, lateral resolution of ~ 30 nm is achievable. Depth profile analysis at the ppm level requires sample areas ~ 10 μm2. Isotope abundance determinations in volumes ~ 1 μm3 require the concentration of the least-abundant isotope to be > 1%.

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