dLow Temperature of formation of Nickel Germanide by reaction of Nickel and Crystalline Germanium
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Low Temperature of formation of Nickel Germanide by reaction of Nickel and Crystalline Germanium Fahid Algahtani1, Patrick W Leech1, Geoffrey K Reeves1, Anthony S Holland1, Mark Blackford2, Gordon Thorogood2, Jeffrey C McCallum3, Brett C Johnson3 1 School of Electrical and Computer Engineering, RMIT University, Melbourne, Victoria, 3001, Australia 2 Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, NSW, 2232, Australia 3 School of Physics, University of Melbourne, Melbourne, Vic, Australia ABSTRACT The formation of nickel germanide has been examined over a range of low temperatures (200-400 °C) in an attempt to minimize the thermal budget for the process. Cross-sectional Transmission Electron Microscopy (TEM) was used to determine the texture of the germanide layer and the morphology and constituent composition of the Ge/NiGe interface. The onset and completion of reaction between Ni and Ge were identified by means of a heated stage in combination with in-situ x-ray diffraction (XRD) measurements. The stages of reaction were also monitored using measurements of sheet resistance of the germanides by the Van der Pauw technique. The results have shown that the minimum temperature for the initiation of reaction of Ni and Ge to form NiGe was 225 °C. However, an annealing temperature > 275 ºC was necessary for the extensive (and practical) formation of NiGe. Between 200 and 300 °C, the duration of annealing required for the formation of NiGe was significantly longer than at higher temperatures. The stoichiometry of the germanide was very close to NiGe (1:1) as determined using energy dispersive spectroscopy (EDS).
INTRODUCTION Germanium has offered unique properties in complementary metal–oxide–semiconductor (CMOS) devices with nearly four times the hole mobility and two times the electron mobility of silicon resulting in higher currents [1-3]. A further advantage of Ge has been its compatibility with the CMOS technology which has been developed for Si. However, an essential requirement in the application of Ge in CMOS technology is the formation of ohmic metal contacts with a low resistance. The solid-state reaction of thin film metals on Ge substrates has been used in the formation of low sheet resistance germanide contacts similar to the formation of silicides in Si devices. Nickel germanide has been amoung the most promising germanides for use in contacts to Ge because it has shown a low sheet resistance of 3.1 Ω/□ for NiGe [4], a low temperature of formation of ~300 °C [4,5] and a grainsize of less than 0.1 µm [6]. In this paper, we have attempted to identify the range of minimum temperature for the practical formation of NiGe in devices. The stages in the reaction were monitored using in-situ phase identification by x-ray diffraction and measurements of the sheet resistance in the reacted film.
EXPERIMENTAL The samples (1.5 x 1.5 cm) used in this study were comprised of crystalline germanium (c-Ge) with a resistivity of 30 Ω.cm. The samples of wafer were initially cleaned
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