Non-destructive Depth Profiling of a Nano Surface by High-energy Synchrotron Radiation XPS

Non-destructive depth profiling with better depth resolution is required for the characterization of nano-materials. Sputter etching is commonly used as the conventional way of depth profiling. However, it causes damage because of atomic mixing and surface roughening by ion bombardment. X-ray photoelectron spectroscopy (XPS) is typically non-destructive analysis, however, XPS with a fixed excitation energy source cannot provide a depth profile without an additional technique. On the other hand, analyzing depth of XPS can be varied with energy tunable excitation source, such as synchrotron-radiation (SR), since the escape depth of photoelectrons depends on their kinetic energy. We can obtain XPS spectra from different analyzing depths by varying the excitation energy. This technique can provide depth profiles of the elements and their chemical states non-destructively. In the present study, thermally oxidized and O-2(+) ion implanted Si(100) surface, initial oxidation process of Fe-Cr (18 %) alloy surface, Ge (2 similar to 4 nm) thin films on Si(100) have been analyzed. The measurements have been performed at KEK-PF, Tsukuba using 1.8-6.0 keV X-ray. XPS spectra clearly show depth dependences, which can be interpreted into depth profile. Chemical state changes at the surface/interface are also clearly observed.