Formation and Morphology Evolution of Nickel Germanides on Ge (100) under Rapid Thermal Annealing
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Formation and Morphology Evolution of Nickel Germanides on Ge (100) under Rapid Thermal Annealing K.Y. Lee 1, S.L. Liew 1, S.J. Chua 1, D.Z. Chi 1, H.P. Sun 2 and X.Q. Pan 2 1 Institute of Materials Research and Engineering, Singapore. 2 Department of Materials Science, University of Michigan, Ann Arbor, Michigan, USA. ABSTRACT Phase formation and interfacial microstructure evolution of nickel germanides formed by rapid thermal annealing in a 15-nm Ni/Ge (100) system have been studied. Coexistence of a NiGe layer and Ni-rich germanide particles was detected at 250 oC. Highly textured NiGe film with a smooth interface with Ge was observed. Annealing at higher temperatures resulted in grain growth and severe grooving of the NiGe film at the substrate side, followed by serious agglomeration above 500 oC. Fairly low sheet resistance was achieved in 250-500 oC where the NiGe film continuity was uninterrupted.
INTRODUCTION As it becomes increasingly difficult to further improve Si-based CMOS performance with traditional device scaling, Ge-based devices have recently attracted a great interest for highperformance logic application, due to its lower effective mass and high carrier mobilities (two times higher for electrons and four times higher for holes as compared to those in Si). While the lack of a stable native germanium oxide has been the main obstacle for its use in CMOS devices, recent development of next generation high-k gate dielectrics allows for the fabrication of high performance Ge-based MOSFETs [1]. The potential use of Ge in future MOSFETs has triggered the active search for suitable germanides, which can be formed in a self-aligned manner through solid-state reactions of Ge and metals as their silicide analogues, as contact metallization materials. TiGe2, CoGe2, and NiGe are three most extensively studied germanides so far. For TiGe2 and CoGe2, though possessing low resistivity, the formation of low resistivity digermanide phases require fairly high processing temperatures (>800 oC for TiGe2 and >500 oC for CoGe2) [2], thus not suitable for Ge-based device fabrication that requires low temperature process, preferably below 500 oC to minimize Ge out diffusion. For NiGe, on the other hand, it can be formed at temperature as low as 270 oC and has a low resistivity comparable to that of NiSi. However, most of the studies on NiGe formation up to date have been carried out using furnace annealing or in-situ annealing by slowly-ramping annealing temperature, rather than using rapid thermal annealing processing (RTP) annealing, and also with less emphasis on morphological evolution [3]. In this study, phase and microstructure stability of NiGe, which can be formed with low thermal budget by RTP annealing, has been investigated.
EXPERIMENTAL DETAILS Pure Ge(001) substrates (n-type; 0.4 Ω.cm) were used in this study. In order to remove native oxide and organic contamination on the surface, the substrates were cleaned using an
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aqueous HF solution (20% by volume) for one minute before loading into
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