Based on the ITRS's report, typical dimensions of wires and contacts in nanoelectronics shrink down to 50 nm by 2010. Hence, there will be increasing demands for ultra shallow and uniform silicides (single-crystal epitaxial silicides) in nanoscales. Among the most attractive silicides, CoSi2 is preferable to TiSi2 because of no scale effect on the resistivity. Epitaxial growth on Si(100) substrates has shown to be far less straightforward than on Si(111) ones which are not widely used in the semiconductor technology. Therefore, modified methods have to be applied for preparing the epitaxial layers on Si(100) substrates.
In this research, using XRD analysis, we have studied epitaxial formation of CoSi2 nanolayer by solid state reaction of Co-Si in refractory metal intermediated or capped layer systems. Furthermore, for the capped layer systems, we have also studied thermal stability of Ag/CoSi2 contact nanolayer, using Rs, RBS and AFM techniques. Thin films of Ta(10nm) as well as W(10nm) as the refractory metal intermediate or cap layers, and also Co(10-15nm) and Ag(50nm) were deposited on Si(100) substrate by DC magnetron sputtering. Heat-treatment of the samples was performed from 500 to 1000°C in an N2 environment for 30min. It has been shown that both Ta and W refractory interlayers resulted in formation of epitaxial CoSi2 nanolayer with (100) texture and Rs of about 1Ω/sq at 900°C. However, the grown CoSi2 layer was thermally unstable at 1000°C in the Ta intermediated layer system, in contrast of the W intermediated layer system with a stable silicide layer. We have found that use of W cap layer cannot yield a single crystalline CoSi2 phase. But, a Ta cap layer resulted in formation of epitaxial CoSi2(100) layer even in a lower temperature of 800°C. The Ag layer was thermally stable up to 500°C, and formation of Ag/CoSi2 contact with Rs of about 1 Ω/sq has been occurred at 800°C. Again, in presence of the Ta layer, the grown CoSi2 layer was thermally unstable at 900°C. It has been also found that a W or Ta silicide was formed on top of the Co silicide thin film structures as a cap layer.
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