DEPTH-RESOLVED SOFT X-RAY EMISSION SPECTROSCOPY OF Si-BASED MATERIALS

Abstract

We discuss a soft X-ray emission (SXE) valence band (VB) spectroscopy method for the study of the electronic structure and chemical phase composition of solids in a near-surface region with depth resolution. The depth information is obtained by variation of the energy of the incident electron beam used to excite the SXE spectra. As the information depth can be varied from about 1 nm to 1 μm in silicon, this method is suitable for the investigation of materials of modern micro- and nanoelectronics. VB → core level (Si 2p or Al 2p) transitions in Si-based materials are used to demonstrate the technique. It was found that the contribution of the signal from the near-surface region (< 1.5 nm) can be substantial (up to 50%) when the primary electron energy does not exceed the Si L 2,3 threshold by more than 150 eV. The technique is applied to Al impurities in a Si matrix, produced by ion implantation. The electronic structure at the Al sites and depth distribution of the Al impurity change markedly after postimplantation annealing. The observed electronic structure after annealing is in agreement with electronic structure calculations for substitutional Al impurities in a crystalline Si lattice.