In ultra-large scale integrated(ULSI) circuits technology, metal silicides have been used to reduce the contact resistance in the source/drain and gate regions. Among the silicides, cobalt disilicide($CoSi_2$) is suitable for nanoscale devices because of its low resistivity and line-width independence, good chemical stability. Moreover, cobalt disilicide can be epitaxially grown on Si substrates due to its small lattice mismatch(-1.2%) and cubic structure. However, the growth of epitaxial (100) $CoSi_2$ on (100) Si substrate has not been successfully realized by physical vapor deposition(PVD) of pure Co and a subsequent annealing process due to the formation of $CoSi_2$ with the various epitaxial orientations. Up to now, several techniques such as interlayer mediated epitaxy, molecular beam epitaxy, and reactive deposition epitaxy have been proposed for the growth of epitaxial $CoSi_2$. However, the techniques require complicated tools and multistep process not commonly used in silicon processing.
In this thesis, a new method for formation of epitaxial $CoSi_2$ layer has been proposed and studied. Epitaxial $CoSi_2$ layers have been formed on a (100) Si substrate at temperature above 600℃ by ex-situ rapid thermal annealing(RTA), followed by the deposition of 17nm thick Co-N film by reactive sputtering of cobalt with (Ar+N2) gas. This method, using cobalt nitride(Co-N) film, offers advantage of no deposition process for diffusion barriers such as Ti, Ta, and chemical oxide.
Two amorphous layers were founded at the interface of cobalt nitride(Co-N) and Si in initial deposition stage. The upper amorphous layer is a silicon nitride state that successfully prevents the diffusion of Co at temperature below 600℃ and lower amorphous layer has a Co-Si intermixing state that comes from the inter-diffusion of Co and Si in the initial deposition stage. The supply of Co into Si by diffusion through the Si-N amorphous layer seems to be low enough, resulting in an epitaxial $CoSi_2$ layer on (100) Si substrate.
A uniform epitaxial $CoSi_2$ layer, with flat interface, has been able to grow on (100) Si substrate using a Co/Co-N bilayer with 1nm thick Co-N film. In the Co/Co-N bilayer structure, the two amorphous layers were also observed at the interface. And then, thin and uniform layer of epitaxial $CoSi_2$ with 20nm thickness could be formed using the bilayer as the thickness of Co on the Co-N interlayer decreases to 7nm thick.
