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The general technique of secondary ion mass spectrometry is now practiced in a number of instrumental variations. For certain problems, any one of these could usefully be employed. However, there is an important class of analytical problems that can be studied only with those instruments of the “small beam type,” that is, an ion microprobe. These problems are those of characterizing fabricated devices, principally in the solid state electronics industry. Regions to be studied on these devices are frequently only a few tens of microns in lateral dimension. The technique has been applied, for example, to the study of adjacent base and emitter regions of a single transistor. Detailed concentration distributions, showing the influence of phosphorus on diffusion of boron double implants were obtained from 25 × 30-µm active areas of 100 × 150-µm rastered regions. Even smaller areas can be successfully analyzed by utilizing reduced beam diameters and a correspondingly reduced raster size. With presently available instrumentation, the practical lower limit on analyzed area is about 4 × 5µm (using a 2/to 3-µm beam and a raster size of 12 × 15 µm). At this level, problems of beam diameter, sensitivity, and surface contamination all become limiting.

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