Surface compositional analysis. Auger electron spectroscopy AES

2 SURFACE COMPOSITIONAL ANALYSIS. AUGER ELECTRON SPECTROSCOPY (AES) 

This particular technique has been the subject of so many reviews and articles (see, for example, refs. 12—17) that no details of its theory or practice need be repeated here. The important feature lies in its ability to measure surface composition with a sensitivity of 1—0.1% for any particular surface atom (except H). In absolute terms, the accuracy is probably not better than 20% (unless very well-defined standards are available), but the relative accuracy can be better than 5%, with approximately the same reproducibility. 

AES has been applied in three areas of semiconductor surface studies. The simplest is the assessment of amounts of contamination present on a surface, and the absence of peaks other than those associated with the substrate is used effectively to define an atomically clean surface. It should be realised, however, that there could still be up to 0.01 monolayer, or 1013 atoms cm-2 of any element (hydrogen cannot be detected) on the surface, even though no additional Auger features are present. 

The second application is to the direct measurement of adsorption-desorption processes using the Auger peak height of the particular element as a monitor. The principal limitation is the possible influence of the electron beam on the adsorbate, which can result in beam-induced desorption, adsorption or dissociation. The basis of electron-stimulated desorption (ESD) was established some time ago independently be Menzel and Gomer [38] and Redhead [39]. Electron impact causes Franck—Condon transitions of bound electrons in the adsorbed species into excited states. There is, therefore, a probability of dissociation with subsequent desorption of the particular species involved. As an example of these effects on semiconductor surfaces, Joyce and Neave [40] have reported results on silicon, while Ranke and Jacobi [41] have discussed the electron-stimulated oxidation of GaAs. 

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