Microstructural Investigation of the TiSi 2 /Si (111) Interface
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MICROSTRUCTURAL INVESTIGATION OF THE TiSi 2 /Si (111) INTERFACE A. CATANA, M. HEINTZE, P.E. SCHMID, P. STADELMANN AND F. LEVY Institute of Applied Physics, Swiss Federal Institute of Technology 1015 Lausanne, Switzerland
ABSTRACT HREM was used to investigate the microstructure and bonding configuration at the interface between TiSi2 and Si (111). The interpretation of the micrographs requires extensive image calculations which were carried out for the first time on this very complex silicide/silicon system. Four different interface models are presented and the corresponding computed interface images are compared with the experimental image. Contrast analysis shows that a model in which a final plane of Ti abuts a layer of Si with a configuration typical of bulk Si best matches the observations. Moreover, the presence of Ti at the interface seems to stabilize a terminal plane of Si with triple dangling bonds. INTRODUCTION The requirements of VLSI technology are strongly related with the great interest in the study of metal silicides and their interfaces with silicon. Furthermore, the investigation of the interface microstructure and relative atomic configurations is essential for the study of the interface chemistry and electronic structure. The silicide/silicon couples can be divided in two main groups. The first one is composed of systems showing single crystal epitaxies with respect to silicon, such as NiSi 2, CoSi 2 and the recently observed CaSi2 [1,2,3]. The second group consists of silicides which also grow epitaxially or pseudo-epitaxially but exhibit a polycrystalline structure. The silicides belonging to this family are Pd 2 Si, PtSi, IrSi 3 [4,5,6] and TiSi 2 [7]. Among them, TiSi 2 is a very interesting candidate for the study of interfaces were two very different crystals must match. In this study, HREM and electron diffraction are combined with image and crystallographic analysis in order to investigate the interface microstructure and epitaxial relations between TiSi 2 and Si (111) substrates. In particular, models of possible interface bonding configurations are presented and discussed using contrast analysis. SAMPLE PREPARATION Si (111) substrates are first thermally cleaned at 950 *C for 20 seconds under UHV conditions (7 x 10-Pa). Subsequently, about 25 nm Ti is deposited by a differentially pumped e-gun. The sample is then annealed by Joule heating the substrate either at 700 'C or 1000 0C. The chemical composition and contaminants are controlled by electron spectroscopy. The layer morphology and related phenomena are discussed elsewhere [8]. Both flat-on and cross-sectional thin samples were prepared for the TEM studies using conventional ion-thinning techniques. TiSi 2 STRUCTURES AND LOCAL EPITAXIES At temperatures below 5000C, the titanium silicidation yields TiSi 2 with a metastable structure (C49). Higher temperature anneals (> 500'C) transform this first phase into the Mat. Res. Soc. Symp. Proc. Vol. 139. 01989 Materials Research Society
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