RuO 2 /SiO 2 /Si and SiO 2 /porous Si/Si interfaces analysed by SIMS Michal C ´ wil a,b, * , Piotr Konarski a , Michal Paja ˛k c , Tomasz Bieniek c , Andrzej Kosin ´ski d , Krzysztof Kaczorek a a Industrial Institute of Electronics, ul. Dluga 44/50, 00-241 Warszawa, Poland b Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warszawa, Poland c Faculty of Electronics and Information Technologies, Warsaw University of Technology, Koszykowa 75, 00-662 Warszawa, Poland d Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland Received 12 September 2005; accepted 15 February 2006 Available online 2 May 2006 Abstract Compared are interfaces between thin silicon oxide layers and two substrates bulk silicon and porous silicon. About 2 mm thick porous silicon was prepared by an electrochemical etching of Si in HF solution. Oxide layers were formed by thermal oxidation. Part of SiO 2 /Si samples were covered with 50 nm RuO 2 oxide. SIMS depth profiles of these interfaces were performed using ultra-low energy (880 eV) and low energy (5 keV) argon ion beams at several incidence angles. Positive and negative secondary ions were analysed by quadrupole mass spectrometer QMA 410 Balzers during Ar + bombardment with the use of 06-350E Physical Electronics ion gun. Charge build-up effects during positive secondary ion detection were observed dependent of the thickness of silicon oxide layer. The SiO 2 /Si interface regions characterised by SIMS show differences related to the kind of a substrate used. In case of 50 nm SiO 2 /porous Si interface, characteristic oxygen depletion region (20 nm thick) is present on the porous silicon side. The observed depletion was confirmed also by Auger depth profiling. The depletion formation mechanism is explained on the basis of ion beam induced redeposition of oxygen inside the pores. # 2006 Published by Elsevier B.V. Keywords: Porous silicon; Nanopores; Silicon oxide nanostructure; SIMS; Depth profile analysis; Oxygen depletion; Charge build-up effect 1. Introduction Porous silicon (PS) opens new perspectives in areas until recently closed for silicon. Properties of this material depend strongly on porosity grade, pore dimensions, etc. Oxidation behaviour of PS is important in usage of this material in sensor and electroluminescence applications [1,2]. Also oxidation is the main ageing phenomenon in PS [3]. In this paper we compare the interface properties of thin silicon oxide layers formed at two substrates bulk silicon and PS. SIMS depth profiles of the oxide layers were performed using 5 keV argon beam. In order to reduce ion beam mixing effects SiO 2 /Si interfaces were also analysed using ultra-low energy (880 eV) ion beam. Several incidence angles of ion beams used in our experiment allowed us to describe the phenomenon of oxygen redeposition inside the pores. 2. Experimental Two kinds of silicon substrates (bulk and PS) were used for silicon oxide layers formation. PS was prepared by anodic etching. The silicon wafer: Si (100) p-type, B-doped, and plat- inum electrode were immersed in water, isopropanol and HF solution. Application of 10 mA/cm 2 current density and appro- priate time of etching allowed to get 2 mm thick porous layer with dominant pore orientation perpendicular to the surface of a wafer [4]. After drying for 2 h in 200 8C in nitrogen, oxidation step was performed in high temperature oven. Solid oxide layers were formed on PS as well as bulk silicon wafers in the same furnace. The oxidation conditions however were different. PS samples were thermally oxidised in 750 8C and bulk silicon in 1000– 1100 8C, obtained SiO 2 layers on PS were 50 nm thick. SiO 2 layers on bulk Si were 5, 15, 22, 50, 65, 83 nm thick. Part of SiO 2 / Si samples was covered additionally with 50 nm RuO 2 oxide. Depth profile analysis of the obtained samples was performed with SIMS and Auger electron spectroscopy (AES). SIMS analyses were performed on SAJW-05 apparatus equipped with 06-350E Physical Electronics ion gun and www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 7058–7061 * Corresponding author. Tel.: +48 22 8319271; fax: +48 22 8312160. E-mail address: cwil@if.pw.edu.pl (M. C ´ wil). 0169-4332/$ – see front matter # 2006 Published by Elsevier B.V. doi:10.1016/j.apsusc.2006.02.215