ABSTRACT
There are many cases in which the precise composition of a thin film radically affects its properties. Sometimes, the composition is stable since the material is an element or stable stoichiometric compound, but even then there can be doubts. Has that stoichiometry actually been achieved in manufacture? Is that pure element contaminated? For alloys, such as SiGe, the whole electrical performance of the layer or of the next strained silicon epilayer will depend upon the composition. It is a parameter that must be measured and controlled and is a particular problem when films get very thin. The classical analytical methods such as optical spectroscopy or conventional x-ray fluorescence (XRF) do not then work well. Optical spectra may be very different in very thin films, and though XRF spectra will be true to the volume sampled, the probing beam will often excite fluorescence in several layers.
