Formation of Ni mono-germanosilicide on heavily B-doped epitaxial SiGe for ultra-shallow source/drain contacts
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Formation of Ni mono-germanosilicide on heavily B-doped epitaxial SiGe for ultra-shallow source/drain contacts Christian Isheden*, Johan Seger, Henry H. Radamson, Shi-Li Zhang and Mikael Östling KTH, Royal Institute of Technology, Department of Microelectronics & Information Technology, P.O. Box Electrum 229, SE-164 40 Kista, Sweden. *[email protected] ABSTRACT The formation of Ni germanosilicides during solid-state interaction between Ni and heavily B-doped strained epitaxial Si1-xGex films with x=0.18, 0.32 and 0.37 is studied. No NiSi2 is found in these samples even after annealing at 850 oC, which can be compared to the formation of NiSi2 at 750 oC on Si(100). Resistance and diffraction studies for the Si0.82Ge0.18 sample indicate that NiSi0.82Ge0.18 forms and the NiSi0.82Ge0.18/Si0.82Ge0.18 structure is stable from 400 to 700 °C. For the NiSi1-uGeu formed in all Si1-xGex samples, where u can be different from x, a strong film texturing is observed. When the Ge fraction is increased from 18 at.% to 32-37 at.%, the morphological stability of the film is degraded and a substantial increase in sheet resistance occurs already at 600 oC. The contact resistivity for the NiSi0.8Ge0.2/Si0.8Ge0.2 interface formed at 550 oC is determined as 1.2×10-7 Ωcm2, which satisfies the ITRS contact resistivity requirement for the 70 nm technology node. INTRODUCTION As the MOSFET device is scaled down, the source/drain extension (SDE) junction depth has to be scaled proportionally to minimize the short-channel effect. However, ultra-shallow junctions formed by ion implantation with a graded doping profile can lead to an unacceptably high contact resistivity after contact metallization using self-aligned silicide (salicide) technique, since the surface Si layer with heavy doping is consumed by silicidation and the actual metal-Si contact is located in the region with a relatively low doping concentration. To overcome this difficulty, raised or elevated S/D junctions with selective epitaxial growth of Si or Si1-xGex on the S/D regions can be used [1,2]. P-type Si1-xGex is particularly suitable for this application because it gives rise to a lower Schottky barrier height than p-type Si when being contacted with a silicide typically of a work-function in the middle of Si bandgap [3]. It also allows for incorporation of more B than in Si [4,5], which can further lower the contact resistivity. Using Ti for the salicide process leads to several problems as the device dimensions are reduced to the sub-100 nm regime. These problems include silicide bridging over the spacers, incomplete formation of the low-resistivity C54 phase in small areas, and high temperature formation. CoSi2 is not an ideal candidate either because its formation is accompanied with a high Si consumption and becomes difficult in the presence of Ge [6]. The use of NiSi helps overcome many of these problems in terms of formation in fine structures and Si consumption [7]. On Si1-xGex, the formation of NiSi1-uGeu is straightforward and the formation of NiSi2 is inh
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