Development of hard x-ray photoelectron spectroscopy using synchrotron radiation x-ray up to 30 keV.

Hard X-ray photoelectron spectroscopy (HAXPES) is a powerful tool for investigating the chemical and electronic states of bulk and buried interfaces non-destructively due to its large probing depth. To obtain a much larger probing depth and measure deeper regions than conventional HAXPES, we have developed a high-energy HAXPES (HE-HAXPES) system excited by photon energies up to 30 keV. This system is achieved by combining an applied bias voltage on the sample with a conventional hemispherical electron energy analyzer. By utilizing this system, we successfully observed a Si 1s peak from the bulk-Si substrate underneath the 110-nm-thick SiO2 film at a photon energy of 30 keV. Moreover, the system found that the asymmetrical spectral shape of the Si substrate signal originated from the electronic state, which is upward band bending formed at the interface between the SiO2 film and Si substrate. The HE-HAXPES system, excited by photon energy up to 30 keV, could be a very useful tool to yield genuine insights into the chemical and electronic states in deeply buried regions.