X-Ray Photoelectron spectroscopy
X-ray Photoelectron Spectroscopy/Electron Spectroscopy for Chemical Analysis
X-ray Photoelectron Spectroscopy (XPS), also called Electron Spectroscopy for Chemical Analysis (ESCA) is a surface chemical analysis technique. This technique is used to measure the elements and chemical states of materials for concentrations above 0.1 to 1 Atomic % depending on the element. XPS uses an X-ray beam to irradiate the sample and thus is an extremely surface sensitive analysis measuring only the outermost 20-50 Å of a surface. Once the electrons are ejected, the quantity and energy of electron is measured indentifing the species and relative amount found in the sample. Used in conjunction with an Ar+ ion beam, elemental and chemical composition can be characterized as a function of depth. All elements except H and He can be detected using this technique.
The advantages of X-ray Photoelectron Spectroscopy is its ability to analyze non-conducting materials, such as ceramics and plastics or films such as SiO2 or SiN, with minimum charging effects. Another advantage is the ability to relate small shifts in the electron energy peak positions to differences in the chemical state thus differentiating between SiO2 and SiN for example. Common applications for XPS are determining thin film composition for process development or process control, analyzing for surface contamination on failing materials, looking at interfaces or verifying surfaces are free of residual materials. Where XPS is more surface sensitive than an electron technique (EDS) the lateral spot size is generally larger requiring an area approximately 100 X 100 microns.