Study of silicon/oxides interfaces by means of Si2p resonant photoemission Massimo Tallarida ⁎, Dieter Schmeisser BTU-Cottbus, Konrad-Wachsmann-Allee 17, 03046, Cottbus, Germany abstract article info Available online 17 August 2008 Keywords: Resonant photoemission Auger spectroscopy Si oxide interface states inter-atomic Auger decay In this paper we show results from resonant photoemission experiments where energy dispersive curves (EDC) were collected at various photon energies around the Si2p absorption edge. From the complete collection we have extracted the spectrum measured at the photon energy of 125 eV and studied the Auger feature included in the EDC. From the comparison of the Auger line of the bulk SiO 2 with the expected transitions we demonstrate the occurrence of inter-atomic transitions in the bulk oxide. Comparing the Auger line from the bulk oxide with that from a native oxide we may observe the occurrence of inter-atomic transitions localized at the interface. We propose an interpretation of this result by considering the geometry at the interface. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Due to its technological importance the SiO 2 /Si interface is one of the most extensively investigated semiconductor-oxide system [1]. In particular, the SiO 2 /Si interface has been investigated by many spectroscopic techniques like core level photoemission, which has been the most frequently used [2], producing many experimental results of both the bulk SiO 2 and its interface with Si that have been interpreted using theoretical calculations of the electronic properties [3]. In this context the Auger spectroscopy is usually considered of minor importance. There are several reasons, first because of the intrinsic complexity of the involved processes that lead to an increased difficulty in the interpretation of the data. Second, because, contrarily to the photoemission spectroscopy, it is impossible to change the surface sensitivity of the Auger spectroscopy by only changing the photon energy. Anyway, these reasons are insufficient to explain why the recent literature is poor of detailed investigations of the SiO 2 /Si interface through the Auger spectroscopy [4,5]. We will show that the Auger spectroscopy can indeed delivery important information about this system, by identifying transitions happening in the bulk oxide and by comparing the Auger data of the bulk and the native oxides. We also show that the photon energy at which the Auger spectra are measured plays an important role in the results. In fact, we have extracted the Auger spectra from resonant photoemis- sion measurements at energies near the Si2p absorption energy. At those energies the interaction between the excited core electron and the valence electrons involved in the Auger decays is very strong and may induce unexpected behaviors. 2. Experimental All experiments were carried out at the Bessy II synchrotron radiation facility, Berlin, at the undulator beamline U49/2. The total resolution was set to 50 meV for all measurements. All Auger spectra that we show were taken from EDC measured in the binding energy range 0–80 eV at various photon energies. The two samples used for the measurement were a commercial 50 nm thick SiO 2 film, grown thermally on an highly n- doped Si(111) substrate; and a 1.5 nm thick native oxide grown on an Si(001) substrate. 3. Results and discussion: bulk oxide features in the Auger spectrum First we show and discuss the Si Auger line for the bulk SiO 2 . With “bulk” SiO 2 we mean the 50 nm thick SiO 2 , and with “native” SiO 2 we mean the 1.5 nm thick native oxide. Due to the large thickness of the bulk oxide, much larger than the electronic mean free path, we expect that the different substrate orientations do not influence the interpretation of our results. In Fig. 1 we show the Si LVV Auger spectrum in the range of 45 eV to 95 eV kinetic energy. Also, in the inset of Fig. 1 , the complete EDC spectrum measured at 125 eV is included. The valence band spectrum has three main peaks at 7.5 eV (peak a), 11.5 eV (peak b) and 14.5 eV (peak c) which are due to the O2p lone pair, and to the bonding O2p bound to hybridized Si3p and Si3s orbitals, respectively [6]. At about 25 eV binding energy is the O2s peak (peak d). We could understand the origin of the peaks in the Auger line referring to the usual interpretation of the Auger process from valence electrons, for which only intra-atomic transition are allowed [4]. In the case of SiO 2 at the Si2p edge, only electrons with Si character should participate to the Auger transition. As described above, only peaks b and c have a considerable contribution from Si-derived states, and, being about 3 eV the energy difference between these two peaks, the Thin Solid Films 517 (2008) 447–449 ⁎ Corresponding author. Angewandte Physik-Sensorik Brandenburgische Technische Universität Konrad-Wachsmann-Allee 17, D-03046 Cottbus, Germany. Tel.: +49 355 693099; fax: +49 355 693931. E-mail address: tallamas@tu-cottbus.de (M. Tallarida). 0040-6090/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2008.08.070 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf