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Auger

Auger Electron Spectroscopy, AES

Theory of Operation. Atomic core ionization of nuclides within the sample occurs as a result of interactions with the electron beam. As a result of this inner core ionization, the electron from a higher energy level (shell) within the ionized atom drops down in energy to fill the vacancy in a lower orbital. The quantized energy difference between the two levels is then given up via either X-ray photon emission or via the radiationless Auger process yielding the auger electron.  Energy analysis of the emitted Auger electron provides elemental identification, and counting of the relative numbers of Auger electrons at the various energies provides semi-quantitative information. The technique is surface sensitive due to the limited escape depth of the Auger electrons, typically on the order of 3-30 Angstroms.

To provide information about subsurface composition and allow depth profiling capabilities, the surface is removed via in-situ ion milling (sputter etching) with an argon ion beam. Scanning or rastering of the electron probe beam allows for elemental mapping capabilities. An ultra-high vacuum (10-10 Torr) in the analytical chamber is necessary in order to prevent re-adsorption of sputtered species or permanent gases onto the freshly sputtered sample surface.

Auger analysis is used to characterize surface contaminants which may inhibit bondability and solderability, contribute to surface leakage or constitute visual rejects. It is also used for characterization of multi-layer structures to monitor the degree of interlayer blend or detect contaminants at various interfaces. Comparative analyses of "good" vs. "bad" samples are common. The sample must be sized to a maximum of approximately I cm x I cm. Samples should not be coated. Due to charge build up at the surface from electron beam bombardment, analysis of thick insulators is limited. Auger electron spectroscopy should be considered a destructive analysis technique.  Auger survey spectrum and a depth profile.

Gideon Analytical Labs  80 Loughran Ln Highland NY 12528-2838      845-255-5356   info@gideonlabs.com 

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