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CoSi2 formation using a Ti capping layer – The influence of processing conditions on CoSi2 nucleation. C. Detavernier, R.L. Van Meirhaeghe Department of Solid State Sciences, Ghent University, Krijgslaan 281/S1, B-9000, Gent, Belgium

K. Maex IMEC, Kapeldreef 75, B-3001 Leuven, Belgium. also at E.E. Dept, K.U. Leuven, B-3001 Leuven, Belgium.

ABSTRACT A reactive Ti capping layer is needed to getter oxygen contamination and to make the cobalt silicidation reaction a more robust process. However, the presence of a Ti capping layer induces two other effects (in addition to the beneficial gettering of oxygen impurities) : the formation temperature of CoSi2 is increased and the CoSi2 layer has a strong (220) preferential orientation. Because of the current technological importance of the Ti/Co/Si system, we have made a detailed investigation of the influence of several process parameters (annealing temperature, selective etching, layer thickness) on the nucleation of CoSi2 in the Ti/Co/Si system. Moreover, it is shown that the addition of Ni (i.e. a Ti/Co/Ni/Si or Ti/Ni/Co/Si structure) causes a decrease of the CoSi2 nucleation temperature. INTRODUCTION It is well known that cobalt silicide formation is rather sensitive to oxygen impurities [1]. To improve the robustness of the cobalt silicidation process, a reactive Ti capping layer may be used to protect the silicidation reaction from oxygen contamination [2-5]. However, the Ti capping layer does not act as a purely passive, protective coating during the silicidation reaction. Instead, the presence of a Ti capping layer directly influences the nucleation of the CoSi2 [6] : firstly, the presence of the capping layer induces an increase in the formation temperature of CoSi2 (by about 60-80°C). Secondly, the CoSi2 that is formed in the presence of a Ti capping layer has a strong preferential (220) and (400) orientation. In a standard two-step SALICIDE process, several parameters must be chosen : layer thickness, temperature and duration of RTP1, selective etching chemistry and temperature and duration of RTP2. In this work, a detailed study was made to determine the influence of several processing parameters on the nucleation temperature and preferential orientation of CoSi2 in the Ti/Co/Si system. The largest increase in nucleation temperature is observed for increasing thickness of the Ti capping layer, decreasing thickness of the Co layer, increasing RTP1 temperature and single step etching. The amount of preferential (220) orientation is correlated with the formation temperature : the higher the temperature at which the CoSi2 is formed, the stronger the preferential orientation. In this paper, we will mainly focus on the effects of capping layer thickness and selective etching. Moreover, we will briefly discuss the effect of Ni addition (i.e. a Ti/Co/Ni/Si or Ti/Ni/Co/Si structure) on the nucleation of CoSi2. K7.4.1

EXPERIMENTAL We used p-type Si(100) substrates (Na = 1013-1014 cm-3). Ti and Co were deposited by e-beam evaporation in a vacuum of 10-6 mbar. Depositio