SIMS
SIMS
Dynamic Secondary Ion Spectrometry
Cameca SC ULTRA
Technique
Atoms or groups of atoms are etched by a primary ion beam (0.25÷20keV). A small fraction of these (typically 1%) is ionized and can therefore be analyzed according to the mass/charge ratio. Either a magnetic sector or a quadrupole are generally used as mass spectrometers. Typical performances of the SIMS technique are the ability to detect each isotope of the periodic table with detection limits ranging from 1ppm to 1ppb, a mass resolution M/DM up to 20000, a lateral resolution of the order of 1µm and a depth resolution of 1nm.
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Two distinct approaches towards lateral resolution are used in SIMS instruments. Lateral resolution is in fact either associated with the use of a finely focused primary ion beam (ion microprobe), or with the optics dealing with secondary ions in such a way as to preserve their spatial relationships (ion microscope). | ||||||||||||||||||||||||||||
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Lateral resolution is therefore limited by the primary beam diameter in the former case and by lenses aberrations in the second case. The sequential detection of masses simultaneously generated makes the technique best suited for depth-profiling. The most important feature is in fact its ability to follow elemental depth distributions with very low detection limits and with high lateral resolution. As a consequence, wide applications of dynamic SIMS are found primarily in microelectronics (depth profiles of dopants and impurities are the typical examples), but also in metallurgy, geology and biology. |
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Cameca SC ULTRA (installed July 2001)
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