Phase Formation in Ti (Ta)-Ni and Co-Ti Films Deposited on (001)Si in N 2 Atmospheres.
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Phase Formation in Ti (Ta)-Ni and Co-Ti Films Deposited on (001)Si in N2 Atmospheres. A.L.Vasiliev1, M.Aindow1, A.G.Vasiliev 2,3, I.A.Horin 2, A.A.Orlikovsky2 1. Department of Metallurgy and Materials Eng., Institute of Materials Science, Unit 3136, University of Connecticut, Storrs, CT 06269-3136 2. Institute of Physics and Technology Russian Academy of Sciences, Moscow, Russia, 3. Moscow State Institute of Radioengineering, Electronics and Automation (Technical University), Moscow, Russia. ABSTRACT A series of electron microscopy investigations on the microstructure produced by surfacediffusion reactions between Si substrates heated to 700-800ºC and Ti-Co, Ti-Ni or Ta-Ni alloys deposited in a nitrogen ambient with and without barrier layers are described. The TEM data show clear phase separation into TaSi2 and NiSi2 for the Ta-Ni film deposited in a high N2 pressure ambient. Deposition at lower N2 pressure led to the formation of a mixed Ni-Ta-Si layer. The phase separation effect was also absent for Ni-Ti films even at high N2 pressure. The presence of barrier layers strongly affected the surface diffusion reactions in the Co-Ti-Si system. Formation of Ti-(O) or CoSix amorphous layers at the Si surface prevented the interdiffusion of Si and Co, such that even pure Co or Co2Si layers could be formed. INTRODUCTION Silicide and nitride layers play key roles in sub-micron ultra-large scale integrated (ULSI) devices. The TiSi2 contact layers, which were originally used in ULSI technologies, have now been replaced by CoSi2 which has a higher thermal stability, lower resistivity and fewer problems in the self-aligned process [1-3]. It is, however, generally accepted that sub-0.1µm ULSI technologies will require the implementation of nickel silicide, because of the lower temperatures at which the silicide can be formed, limited diffusion, lower silicon consumption, lower mechanical stresses, and lower contact resistance [4-8]. TiN has been used as the nitride barrier layer to prevent interdiffusion between the Si and Al metallization layers in ULSI devices. However, problems arise for the latest generation of ULSI devices with Cu metallization because the diffusivity of Cu through polycrystalline TiN is too high [9] despite attempts to optimize the barrier properties by, for example, O incorporation during growth [10]. Ta-Si-N films have been proposed as more effective diffusion barriers between Si and Cu [11]. It would be advantageous if one could combine the formation of contact layer and diffusion barrier into a single process by, for example phase separation [12]. In a recent study of solid state reactions during multi-component deposition and subsequent annealing (at 600-700ºC) of Co/Ti, Co/Hf and Co-Ni/Ti films, it was shown that uniform CoSi2 layers with flat interfaces and intermediate Co-Si-Ti or Co-Si-Hf barrier layers could be formed on Si [13,14]. Solid phase reactions in the Ti-Co-N system after annealing at 850ºC gave rise to the formation of separate TiN and CoSi2 layers [15]. However the temperat
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