Three Dimensional Secondary Ion Mass Spectrometry

The determination of the three dimensional distributions of impurities and dopants at low concentrations in solid materials is possible using either ion probes or ion microscopes. The potential depth resolution in such determinations is of the order of 1 nm while the lateral resolution is limited to about 10-100 nm by collision processes. Ion microprobes are approaching these limits while ion microscope lateral resolution is currently ~ 0.5 μm. Ion microprobes have the advantage of a relatively simple ion detection and image formation system but at the expense of speed of data accumulation. Ion microscopes accumulate image information simultaneously over the entire image area but require much more complex image data handling systems. The best ion imaging systems retain all of the dynamic range of the normal ion counting electronics. As improved lateral resolution is achieved, the limits of detection at the same depth resolution must necessarily degrade due to the destructive nature of sputtering. Progress on the many problems of conversion of ion images to quantitative concentration maps is discerned as many applications begin to appear in the literature