Nickel, Platinum and Zirconium Germanosilicide Contacts to Ultra-shallow, P + N Junctions Formed by Selective SiGe Techn
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Nickel, Platinum and Zirconium Germanosilicide Contacts to Ultra-shallow, P+N Junctions Formed by Selective SiGe Technology for CMOS Technology Nodes Beyond 70nm
Jing Liu, Hongxiang Mo, Mehmet C. Öztürk North Carolina State University Department of Electrical and Computer Engineering Centennial Campus, EGRC Building Raleigh, NC27695-7920, U.S.A. ABSTRACT Selective SiGe source/drain technology based on selective deposition of in-situ doped SiGe alloys in recessed source/drain regions can provide junctions with low sheet and contact resistance as well as abrupt doping profiles. This paper examines properties of Ni, Pt and Zr germanosilicides on heavily boron doped SiGe junctions. Our results show that all three metals can form low resistivity germanosilicides on heavily boron doped SiGe alloys. The stability of Ni germanosilicide was found to be limited to about 400°C on undoped SiGe. On heavily boron doped SiGe thermal stability was found to be significantly better possibly due to boron strain compensation. Our findings indicate that on undoped SiGe, thermal stability of Ni germanosilicide could be much enhanced by using a thin Pt interlayer. According to X-ray diffraction analysis, with increasing formation temperature, both Ni and Pt germanosilicides moved toward Ni and Pt monosilicides with signs of excess Ge appearing outside the contact. Analysis of the Pt germanosilicide layers is suggestive of a Ge rich SiGe layer under the germanosilicide. Boron diffusion into Pt and Ni germanosilicides was not observed. On the other hand, a distinct boron peak was observed in Zr germanosilicide suggestive of a stable Zr-B compound. Ultra-shallow junctions with excellent reverse bias behavior were formed using both Ni and Zr germanosilicides. INTRODUCTION One of the key challenges for future CMOS technology nodes is formation of ultra-shallow junctions with a series resistance less than five percent of the channel ‘on’ resistance. According to International Technology Roadmap for Semiconductors (ITRS2001), for technology nodes beyond 65 nm, contact resistance will dominate the junction series resistance and contact resistivities in the range of 1×10-8 Ω-cm2 will be required [1]. It is well established that fundamentally new approaches are required to overcome this challenge due to fundamental limitations of Si. A new technology based on selective deposition of heavily doped SiGe alloys was recently proposed by this laboratory [2]. One of the key advantages of this technology is the lower bandgap of SiGe, which provides a smaller metal-semiconductor barrier height - an essential requirement for low contact resistivity. Recently, we have reported Ni and Pt germanosilicide contacts to heavily boron doped SiGe with a contact resistivity near 1×10-8 Ω-cm2 [3]. In this paper, we compare Ni, Pt and Zr and their bi-layers in forming germanosilicides with emphasis on thermal stability. Sheet resistance, surface morphology, dopant redistribution and junction quality are considered.
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