High-Dose Titanium Ion Implantation into Epitaxial Si/3C-SiC/Si Layer Systems for Electrical Contact Formation
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High-Dose Titanium Ion Implantation into Epitaxial Si/3C-SiC/Si Layer Systems for Electrical Contact Formation Jörg K.N. Lindner, Stephanie Wenzel, and Bernd Stritzker Universität Augsburg, Institut für Physik, D-86135 Augsburg, Germany ABSTRACT High-dose titanium implantations have been performed into ion beam synthesized heteroepitaxial layer systems of Si/3C-SiC/Si(100) in order to study the formation of titanium silicide layers in the silicon top layer. The structure and composition of layers was analysed using RBS, XRD, XTEM and EFTEM. The sputtering rates of 180 keV Ti ions were determined using the lower SiC/Si interface as a marker. A homogeneous surface layer with the stoichiometry of TiSi2 was formed by a nearly stoichiometric implantation and subsequent annealing. The formation of more metal-rich silicides was observed at doses where the peak Ti concentration largely exceeds the TiSi2 stoichiometry and where the total amount of Ti atoms in the top layer is greater than the amount needed to convert the entire Si top layer into TiSi2. Under these conditions, strong solid state reactions of the implanted Ti atoms with the buried SiC layer and the silicon substrate are observed. INTRODUCTION The formation of highly conductive as well as thermally and chemically stable electrical contacts to the wide band gap semiconductor silicon carbide is one of the unsolved and challenging tasks in silicon carbide technology. Transition metals, their silicides and carbides are materials under discussion to solve the contact problem. Frequently, multilayer approaches are attempted [1]. Among the different transition metals which might be used, titanium is particularly interesting for a number of reasons: Titanium forms a variety of silicides, among which the high-temperature phase C54-TiSi2 has been studied to a great extent; it has a specific resistivity as low as 11 µ Scm, and therefore is used as a contact material in silicon CMOS technology [2]. On the other hand, Ti may form cubic TiC which, due to its lattice constant of 4.33 D next to that of cubic SiC (4.36 D), may grow epitaxially on 3C-SiC [3]. As TiC and SiC are isomorphous and fully miscible, high-dose Ti implantation into 3C-SiC leads to the formation of a ternary TixSi1-xC compound by the replacement of Si by Ti atoms from its lattice sites [4]. The aim of the present study is to form a metallic contact layer to a SiC thin film, which is grown as a buried layer in silicon by ion beam synthesis (IBS). The ion beam synthesis of buried homogeneous epitaxial 3C-SiC layers in Si(100) and Si(111) has been studied previously in a series of investigations [5]. It has also been demonstrated that, in addition to Si/SiC/Si layer sequences, it is possible to form Si/SiC/SiO2/Si layer sequences by using SIMOX (separation by implantation of oxygen) substrates instead of silicon [6]. In such a layer sequence, the buried oxide layer may serve as an electrically insulating layer to prevent flooding of the SiC at high temperatures by thermally generated carriers from the Si sub
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