The Prs 2 O 3 /Si(001) Interface: a Mixed Si-Pr Oxide
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The Pr2O3/Si(001) Interface: a Mixed Si-Pr Oxide Dieter Schmeißer, Jarek Dąbrowski1, and Hans-Joachim Müssig1 Angewandte Physik-Sensorik, BTU Cottbus, Postfach 10 13 44, D-03013 Cottbus, Germany 1 IHP, Im Technologiepark 25, D-15236 Frankfurt (Oder), Germany ABSTRACT We studied the Pr2O3/Si(001) interface by a non-destructive depth profiling using synchrotron radiation and photo-electron spectroscopy (SR-PES) at the undulator beam line U49/2PGM2 and ab initio calculations. Our results provide evidence that a chemical reactive interface exists consisting of a mixed Si-Pr oxide such as (Pr2O3)(SiO)x(SiO2)y. There is no formation of neither an interfacial SiO2 nor interfacial silicide: all Si-Pr bonds are oxidized and all SiO4 units dissolve in the Pr oxide. Under ultrahigh vacuum conditions, silicide formation is observed only when the film is heated above 800 °C in vacuum. Interfacial silicates like (Pr2O3)(SiO)x(SiO2)y are promising high-k dielectric materials, e.g., because they represent incremental modification of SiO2 films by Pr ions, so that the interface characteristics can be similar to Si-SiO2 interface properties. The Pr silicate system formed in a natural way at the interface between Si(001) and Pr2O3 offers an increased flexibility towards integration of Pr2O3 into future CMOS technologies. INTRODUCTION CMOS transistor scaling is rapidly approaching the moment when performance limits of traditional materials become critical. Because of the direct proportionality between the channel length in a metal oxide silicon field effect transistor (MOSFET) and thickness tox of the gate oxide, tox is being continuously reduced during the process of miniaturization. If made of SiO2 (as in the existing technologies), a gate dielectric in state-of-the art MOSFETs produced within a few years from now would have to have tox corresponding to less than five atomic layers. This would lead to a drastic increase of the tunneling current; such an increase cannot be accepted, especially in mobile, battery-powered devices. To find a dielectric alternative to SiO2, with electrical properties similar to that of SiO2 but with sufficiently high dielectric constant so that tox can be sufficiently increased poses a significant scientific and technological challenge. Pr2O3, grown heteroepitaxially on Si(001) is a promising candidate to replace SiO2 as the gate dielectric material for sub-0.1 µm CMOS technology [1-3]. For all thin gate dielectrics, the interface with Si plays a key role, and in most cases is a major factor determining overall electrical properties. Most of the high-k metal oxide systems investigated so far have either unstable or heavily defected interfaces to the silicon substrate. In order to maintain high-quality interface, high channel mobility, and good IV characteristics of the MOSFET, it is important to have low defect density and no silicide phase present at or near the channel interface. In this work, we analyze the interfacial stoichiometry of the Pr2O3/Si(001) system using photoelectron spectroscopy
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