Destructive and non-destructive depth profiling using ESCA

While the chemical analysis of a surface has become commonplace using a variety of techniques including Auger Electron Spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA), it is often advantageous to differentiate between the chemistry of the surface and the near surface. The method used to make this distinction depends on the thickness of the layers to be differentiated. If the combined thickness of the layers is greater than 100 Å, then the surface must be physically removed by ion bombardment before the subsurface components can be identified. An example of the chemistry revealed by this method is given in a sputter profile of an eight layer, 3000 Å, metal magnetic tape. The internal interfaces show more oxidation than the bulk of the metal layers. If the combined thickness of the layers is less than 100 Å, then the surface and subsurface components can be identified by non-destructive techniques. This is accomplished by using high energy excitation or by angle resolved studies. Examples will be shown of the change in the surface and near surface chemistry of polystyrene as it is treated in H₂ and H₂O plasmas. The degree of oxidation of the polymer surface can be monitored as a function of reaction depth using angle resolved ESCA. Extending the range of angle resolved studies by using Au Mα X-rays is shown for a native oxide on silicon.