Phase Transformation of Co Silicidation in the Co/Ti- and Ti/Co-Si(100) Systems
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PHASE TRANSFORMATION OF Co SILICIDATION IN THE Co/Ti- AND Ti/Co-Si(100) SYSTEMS 3 3 3 1 2 Feng Hongl, Bijoy K. Patnaik , , Bingzong Li , Ping Liu , Zen Sun , and 1 Rozgonyi George A. 1 Dept. of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695-7916, 2 Dept. of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599-3255 3 Dept. of Electronic Engineering, Fudan University, Shanghai, China
ABSTRACT Co silicide formed via selective diffusion of Co through a Ti interfacial layer has been reported by several groups. In this report, phase identification of the silicide has been further studied for both Co/Ti and Ti/Co multi- and bilayers deposited on p(100)-Si substrates. The samples were either vacuum furnace or RTA annealed from 550*C to 900°C. The Co silicide formation sequence in the Co/Ti-Si systems follows CoSi 2 -+Co 2 Si--*CoSi--*CoSi2 with the formation temperature increasing for each phase. The Co/Ti bilayer CoSi to CoSi2 transformation temperature was lower than that for the six layer Co/Ti system. For the multilayer sample with Co as the first layer in contact with the Si CoSi2 formed at 550*C and then CoSi was observed at higher substrate, temperatures due to the effect of Co supply on disilicide phase instability. Epitaxial CoSi2 growth occured at higher temperatures after the removal of the unreacted upper layers. A 15 l.iD-cm film resistivity was obtained from 50 nm epitaxial CoSi2. INTRODUCTION Deep submicron ULSI device development requires contact structures of transition metal silicides which are uniform, thermally stable, low resistivity 1 and are compatible with ultra shallow junctions[ ]. In addition to nano-scale Cosilicide studies with conventional single layer Co on Si substrate, a variety of procedures for forming Co silicides from bilayer and multilayer Co/Ti on Si substrates have also been reported [2-10]. Epitaxial CoSi2 layers on Si(100) with thicknesses from 12 to 50nm have been produced from Co/Ti-Si structures by two step rapid thermal annealing and furnace annealing. The interfacial Ti layer has been found effective in reducing the Si substrate native oxide layer, and in functioning as a selective diffusion membrane during the Co-Si interaction. Although the interdiffusion scheme in the layered Co/Ti-Si system is more complicated than that in a conventional Co/Si structure, most prior work has concentrated on the interfacial Co-silicide layer. In this paper, the Cosilicide formation sequence from multilayer and bi-layer Co/Ti on Si(100) substrates is described and compared to the conventional Co/Si case, along with issues related to Co silicide phase stability and transformation at higher temperatures.
EXPERIMENTAL The substrates used were p-type, 5 to 9 01 -cm (100) Si wafers. Both six layer and two-layer samples of Co and Ti were deposited sequentially by either dual source thermal evaporation or dual target ion beam sputtering to form six layer and two layer Co(20nm)/:j(IOnm) on Si, or a Co/Ti/Co/Ti(20nm)/Co(10nm) Mat. Res. Soc
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