Contact Resistivity of NiPtSi on n-doped Silicon Activated by Laser Annealing
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1108-A11-02
Contact Resistivity of NiPtSi on n-doped Silicon Activated by Laser Annealing Francois Pagette, Paul M. Solomon, Paul M. Kozlowski, Anna W. Topol, Wilfried Haensch T.J. Watson Research Center, IBM, Yorktown Heights, NY 10598, U.S.A. ABSTRACT Reducing specific contact resistivity of the silicide to silicon interface is advantageous to achieve high planar density and high drive current FET devices. Measuring the differential resistivities at different low voltage bias conditions of four terminal Kelvin test structures with a range of contact sizes has proven particularly effective in characterizing the linearity behavior and specific contact resistivity. This study shows that adding laser activation annealing for an n+ doped silicon contacted by a standard NiPt silicide is found to significantly improve the contact electrical properties. Initial results with only rapid thermal anneal activation show a size dependence of the contact resistivity with non-linear behavior exhibiting maximum resistance at zero bias, and contact resistivities ranging from 4×10-8 Ω-cm2 to 4×10-7 Ω-cm2. Adding laser anneal after the rapid thermal anneal gives ohmic behavior, for contact down to 50nm in size, with a specific contact resistivity of 1×10-8 Ω-cm2. The metal-to-silicide contact resistance was measured separately using a novel test structure and it was confirmed to be negligible. We describe our device structure, our experimental methodology, and the implications of our results for future devices. INTRODUCTION As scaling of high performance CMOS devices continues, contact area and silicon thickness are reduced. Devices like ETSOI FET, FinFET and Trigate FET have become increasingly difficult to contact using conventional techniques. Series resistance components limit intrinsic device current capability which directly impacts device performance. Reducing the specific contact resistivity (ρc) of the silicide to silicon interface, the topic of the current study, is advantageous to achieve high drive current in future devices. The contact resistivity depends exponentially on the Schottky barrier height and the doping level of the semiconductor. The minimum contact resistance (zero barrier height) in the semiclassical limit is the Sharvin resistance, m vth /e2n, where vth is the mean thermal velocity of electrons in silicon, m is the electron mass, e is the electron charge, and n is the electron concentration [1]. For electron concentrations > 1020cm-3 this limiting resistivity is less than 10-10 Ω-cm2, showing that contact resistivities in the 10-9 Ω-cm2 range are technologically feasible. Recent advances in laser annealing techniques are allowing for higher activated dopant concentration and lower barrier heights than have been previously available. This should facilitate the development of an ultra-low ρc technology. For silicide contacted devices, there is an additional interface between the silicide and the metal that has to be accounted for. Since this resistive element is expected to be small compared to the silicide
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