CAN LEIS SPECTRA CONTAIN INFORMATION ON SURFACE ELECTRONIC STRUCTURE OF HIGH-K DIELECTRICS?

While investigating the surface composition of thin layers containing Hf with low energy ion spectroscopy (LEIS) utilizing He

+

ions with energy

E

0

=300÷800 eV, the fine structure of Hf line was observed. Hf spectrum consists of several narrow lines on top of a broad asymmetric peak. The number of lines and their separation does not depend on He

+

incident energy, but rather on the chemical composition of the surface layer: spectrum of metallic Hf is remarkably different from that of HfO

2

, and, on the contrary, is very similar to HfSi

x

. The observed effect is explained in terms of single electronic excitations due to promotion of Hf-He

+

molecular orbitals during impact which leads to the inelastic energy loss of He

+

. Since LEIS is sensitive to the utmost surface layer, the observed effect can be potentially utilized to probe the surface electronic structure of compounds containing Hf.