Nano-laminating of SiO 2 and TiO 2 : Atomic layer deposition as a tool to gain new insight into interfaces
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Nano-laminating of SiO2 and TiO2: Atomic layer deposition as a tool to gain new insight into interfaces Nicolas Sobel and Christian Hess* Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, 64287 Darmstadt, Germany
ABSTRACT Atomic layer deposition (ALD) was used to deposit a laminate structure of alternating SiO2 and TiO2 monolayers onto a Si wafer. The resulting samples were analyzed in detail by Xray photoelectron spectroscopy (XPS) revealing a distinct O 1s signature due to the presence of Si-O-Ti species. These findings are in good agreement with those reported for thin ALD films of TiO2 grown on SiO2.
INTRODUCTION Atomic layer deposition (ALD) is a versatile tool to deposit thin conformal films onto a wide range of planar, porous and powder substrates [1]. In the ALD process, usually two gaseous precursors are alternatingly exposed to the substrate forming chemical bonds to the surface. The excess and byproducts are removed from the gas phase by pumping and purging. A high level of conformity is achieved due to the self-limiting nature of the surface reactions. After exposure to both gases, one monolayer of the thin film material is deposited thus enabling monolayer precision film thickness control in the Ångstrom regime. By repeating the described cycle, thicker films can be obtained. Laminate structures are accessible by using two sets of precursors, which form alternating layers of two different film materials. This new kind of material, deposited by ALD, is a growing field of research. By now, studies focused on the formation of high-κ gate dielectrics in microelectronics with film thicknesses of several nanometers [2,3] or tuning optical thin film properties [4]. Beside the application in the field of microelectronics, thin laminate structures allow for investigations of the interface between two or more material combinations. In the area of thin films with film thicknesses of a few nanometers, far away from bulk-like conditions, the interface has a crucial effect on physical and chemical properties [5]. However, detailed investigation of these effects is often hampered by the low concentration of interface atoms and the low interface sensitivity of most spectroscopic methods. In principle, there are two ways to enhance the signal quality: First, to enhance the sensitivity of the measurement device itself or, second, to increase the interface concentration. To this end, deposition of subnanometer laminates of the interface materials with a thickness of several nanometers may be an interesting approach. In this study, such a laminate-based approach is tested for the SiO2-TiO2 interface. X-ray photoelectron spectroscopy (XPS) is employed for detailed surface analysis. As described in the following, XPS investigations on this interface were reported previously but for differently prepared samples [6,7]. Lassaletta et al. evaporated Ti metal from a wire in the presence of
2.66×10-6 mbar oxygen onto a fused quartz substrate as well as an o
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