XPS depth profiling by changing incident X-ray energy

Excitation energy variable XPS measurements were performed using high-flux soft X-rays from synchrotron radiation. This method enables non-destructive XPS depth profiling by changing the photoelectron attenuation length. In the analysis of a HF cleaned silicon wafer, the present method revealed the presence of a very thin (∼ 1A˚) surface layer of partially oxidized silicon (Siδ+) which would not be detected by conventional Al or Mg Kα X-ray sources.