Silicide engineering: influence of alloying elements on CoSi 2 nucleation
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Silicide engineering : influence of alloying elements on CoSi2 nucleation C. Detavernier*, R.L. Van Meirhaeghe*, K. Maex+0, F.Cardon* *
Vakgroep Vaste Stofwetenschappen, Ghent University, Krijgslaan 281/S1, 9000 Gent, Belgium IMEC, Kapeldreef 75, B-3001 Leuven, Belgium. 0 also at E.E. Dept, K.U. Leuven, B-3001 Leuven, Belgium. +
ABSTRACT Evidence is presented that the nucleation of CoSi2 can be influenced by the presence of small amounts of other elements. The presence of trace amounts of Ti in the CoSi (originating from either a Ti capping layer or interlayer) causes an increase in the CoSi2 nucleation temperature. Moreover, the presence of Ti in the CoSi induces a preferential orientation of the CoSi2 : for an increasing amount of Ti, we observed a transition from polycrystalline CoSi2 over preferential (220) orientation towards epitaxial (400) CoSi2. We observed similar effects for other elements (e.g. Ta, W, C, Mo, Cr). We were able to explain these findings based on the heterogeneous nucleation of CoSi2. INTRODUCTION The presence of a 3-7 nm Ti interlayer (in between the Co and Si substrate) is known to promote epitaxial growth of CoSi2 (Ti Interlayer Mediated Epitaxy, TIME)[1]. Traditionally, this is explained by (1) the ability of Ti to reduce SiO2 and by the fact that (2) the interlayer acts as a diffusion barrier. In this work, we studied phase formation and preferential orientation of the CoSi2 as a function of Ti thickness, both for interlayers (0.1-10 nm) and capping layers (1-10 nm). In case of a thin Ti interlayer (< 1 nm), we observed that the nucleation of CoSi2 is delayed to about 600°C. Moreover, the CoSi2 has a strong preferential orientation and improved thermal stability. For 0.1-0.6 nm Ti, there is a (220) and (400) orientation, while for thicker Ti interlayers ( > 1 nm), there is a strong orientation. Similar results are found for a Ti capping layer (Ti/Co/Si system). Our results indicate that there are two regimes of interlayer thickness wherein the epitaxial growth is achieved by two different mechanisms : for thick interlayers, the function of the interlayer is to slow down diffusion, while for thin interlayers (< 1 nm), the main function of Ti is to improve the grain boundary cohesion in the CoSi. We present a model on heterogeneous nucleation of CoSi2, which explains how even a trace amount of Ti is able to strongly influence the nucleation of CoSi2, because of its influence on interfacial energy. EXPERIMENT For all experiments, p-type Si(100) substrates were used. After cleaning and a final HF dip, the substrates were mounted in an e-beam evaporation system. Co and Ti layers were deposited in a vacuum of 10-6 mbar. Bilayers were deposited without breaking the vacuum. Both the effect of Ti as an interlayer (Co/Ti/Si) and capping layer (Ti/Co/Si) was investigated. To study the
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silicidation reaction, isochronal RTP annealing (30s, N2 ambient) was done at various temperatures. Sheet resistance measurements and grazing incidence X-Ray Diffraction (XRD) were used for phase identifi
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