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Bombardment of a
sample surface with an energetic primary ion beam followed by mass spectrometry
of the emitted secondary ions constitutes secondary ion mass spectrometry
(SIMS). Because secondary ions are either charged positively or negatively,
there are two modes of SIMS: +SIMS and –SIMS. In all commercial instruments,
these two modes are conducted separately.
Today, SIMS is
widely used for analysis of trace elements in solid materials, especially
semiconductors and thin films. D-SIMS is capable of detecting trace impurities
with a sensitivity of greater than one part per billion. The SIMS ion source is
one of only a few to produce ions from solid samples without prior vaporization.
The SIMS primary ion beam can be focused to less than 1 um in diameter.
Controlling where the primary ion beam strikes the sample surface provides for
microanalysis, the measurement of the lateral distribution of elements on a
microscopic scale. During SIMS analysis, the sample surface is slowly sputtered
away. Continuous analysis while sputtering produces information as a function of
depth, called a depth profile. |
