Thickness Effect on Nickel Silicide Formation and Thermal Stability for Ultra Shallow Junction CMOS
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Thickness Effect on Nickel Silicide Formation and Thermal Stability for Ultra Shallow Junction CMOS F. F. Zhaoa, Z. X. Shena, J. Z. Zhengb, W. Z. Gaob, T. Osipowicza, C. H. Pangc, P. S. Leeb, A. K. Seeb a Physics Department, 2 Science Drive 3, National University of Singapore, Singapore 117542. b Chartered Semiconductor Manufacturing Limited, 60 Woodlands Industrial Park D, Street 2, Singapore 738406. c School of Materials Engineering, Nanyang Technological University, Nanyang Avenue 3, Singapore 639798.
ABSTRACT High purity Ni films from 200Å down to 40Å on p-type Si (100) substrates are treated by rapid thermal annealing to form the metastable and stable phases of nickel silicides. The stoichiometric composition of NiSi determined by Rutherford backscattering is independent of the initial Ni thickness under 500ºC annealing. Channeling RBS results reveal that the NiSi growth on Si (100) has no preferred orientation. The sheet resistance as well as surface roughness of thinner films starts to increase at a lower temperature, indicating that thinner films are thermally less stable. Agglomeration of NiSi film agrees with the grain boundary grooving model and occurs more easily within thinner films. The transformation from the NiSi phase to the NiSi2 phase is studied by micro-Raman spectroscopy. This phase transition of thinner films begins at a lower temperature than that of thicker ones. INTRODUCTION Because of its low resistivity, low silicon consumption, low formation temperature and linewidth-independent silicidation, nickel monosilicide (NiSi) is a promising self-aligned-silicide (salicide) candidate for sub-0.1µm CMOS technology [1]. Compared to the most widely used salicides, TiSi2 and CoSi2, NiSi possesses several distinctive advantages for IC device fabrication. For example, the sheet resistance of TiSi2 increases remarkably with decreasing gate linewidth due to incomplete C49 TiSi2 to C54 TiSi2 transformation on narrow lines, while the resistivity of NiSi remains constant down to 0.1µm. Also Ni consumes about 20% less silicon than Co to form a salicide film of the same thickness, making NiSi attractive for applications in ultra shallow junction CMOS [2]. However, the thermal stability of NiSi is worse than TiSi2 and CoSi2 as the high resistivity phase NiSi2 nucleates at 750ºC and film agglomeration occurs even at a temperature as low as 600ºC. Recently, many studies have focused on how to delay the formation of NiSi2 phase and improve the thermal stability of NiSi phase. Pt implantation or interlayer has been demonstrated to be effective, increasing the monosilicide to disilicide phase transition by about 100ºC [3,4]. From the point of view of industrial applications, the effects of silicide thickness and silicon consumption are also critical, especially for 0.1µm technology and below. In this study, the thickness effect of the initial Ni films on the phase formation and thermal stability of nickel silicides are studied using Rutherford backscattering spectroscopy (RBS), micro-Raman spectroscopy (µRS), atom
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