Formation and Characterization of Spe Grown Ultra-Thin Cobalt Disilicide Film
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C. Detavernier, R L. Van Meirhaeghe, F. Cardon Dept. of Solid State Science, University of Gent, Krijgslaan 281/S 1,B-9000, Gent, BELGIUM.
Abstract Ultra-thin epitaxial CoSi2 films formed by Co(3-5nm)/Ti(1 nm)/Si(100) and Co(3-5nm)/Si(lnm)/Ti(Inm)/Si are studied. The multilayers are deposited by ion-beam sputtering. Rapid thermal annealing (RTA) is used for silicidation. XRD, RBS, TEM, AFM, four-point probe, I-V and C-V measurements are carried out for characterization. The XRD spectra show the CoSi 2 film formed by Co/Ti/Si or Co/Si/Ti/Si solid phase epitaxy has, epitaxial characteristic. XTEM shows that the film is continuous. RBS/Channeling shows that the formed CoSi 2 has sharp interface with a minimum channeling yield of Co signal of 401/6. AFM shows that the surface of ultra-thin CoSi 2 film is smooth with a roughness of nearly 0.7 nm. The Rs-T relationship shows that the CoSi 2 films formed by Co/Si/Ti/Si reaction have the best thermal stability (stable up to 900*C). Those formed by Co/Ti/Si reaction are stable up to 850'C, while those formed by Co/Si reaction are only stable up to 750'C. By fitting the experimental I-V and C-V curves of the epitaxial CoSi2 /Si Schottky diodes, barrier heights of around 0.6 eV and close to unity ideality factors are obtained.
Introduction As the size of VLSI devices is continually reduced, it is required to make a uniform, thermal stable and ultra-thin silicide contact to ultra-shallow junctions. This is especially important for SOI
devices. Ultra-thin silicide film may also be utilized to make some novel high speed devices such as permeable base transistor (PBT) and metal base transistor (MBT) in which the film has to be very thin to achieve high performance[l]. Of all the silicides with very low resistivity, CoSi2 is the most attractive one, not only due to its low resistivity (14-20pQ.cm) and good thermal stability, but also due to its good lattice match with Si (the lattice mismatch is only -1.2% at RT), which makes the epitaxial growth of CoSi2 on Si possible. It is difficult to grow ultra-thin CoSi2 films on Si substrate. Thin films always show severe agglomeration and poor thermal stability. Accrording to some reports, the resistance increases significantly after annealing at 700'C [2,3]. An epitaxial CoSi2 film may have a better thermal stability than a comparable polycrystalline layer because of a lower interface fi-ee energy and a lack of grain boundaries. Some methods have been developed to grow ultra-thin epitaxial CoSi2, such as molecular beam epitaxy (MBE)[4], mesotaxy[5] and oxide mediated epitaxy (OME)[6]. Due to their complexity, they are difficult to use in practical applications. The Co/Ti/Si solid phase epitaxy (SPE), which uses a thin Ti layer to induce epitaxial growth of CoSi2 (so the method is also called Titanium Interlayer Mediated Epitaxy TIME)[7], received much attention in recent years. The process has good compatibility with modem VLSI technology, and is capable to fabricate high quality epitaxial CoSi2 . The TIME method ha
