Non-destructive depth profile analysis with better depth resolution is required for the characterization of nano-materials and their fabrication. Sputter etching is commonly used for the conventional way of depth profiling. However, it makes damage of analyzing area because of the atomic mixing and surface roughening. X-ray photoelectron spectroscopy (XPS) is the typically non-destructive analysis, however, XPS with fixed excitation energy source cannot provide depth profile without additional technique. On the other hand, analyzing depth of XPS can be varied with the energy tunable excitation source, such as the synchrotron-radiation (SR), since the escape depth of the photoelectrons depends on their kinetic energy [1]. We can obtain the XPS spectra from different analyzing depth by varying excitation energy. This technique can provide depth profile non-destructively [2]. In the present study, Ge thin films on Si substrate has been analyzed to obtain depth profile of the thin film and buried interface of Ge/Si under the film.
The high-energy SR-XPS (1.8~3.7 keV) measurement has been performed at Beam Line 27A at the Photon Factory in the High Energy Accelerator Research Organization (KEK-PF). The samples used were vapor deposited Ge with 2 and 4 nm thickness on the Si(100) single crystal, respectively. The Si substrate surfaces were treated as two different ways. One of the substrate was chemically treated and subsequently terminated with hydrogen. Another one is just supersonically rinsed with acetone and has native oxide layer.
The XPS spectra clearly show the difference obtained from the varied analyzing depth. The interface under the deposited films can be observed even for the 4 nm Ge sample. Difference between the substrates which have hydrogen termination and native oxide. Chemical state changes at the interface are also observed. These results suggest that the SR-XPS can be applicable for non-destructive depth profile analysis of surface and buried interface.
[1] S. Tanuma, C.J. Powell, D.R. Penn, Surf. Interface Anal. 17 (1991) 911.
[2] H. Yamamoto, Y. Baba, T.A. Sasaki, Surf. Sci. 349 (1996) L133. |