A Study on Solid Phase Reactions of Ni and Pt on Si-Ge Alloys as Contacts to Ultra-Shallow P + N Junctions for CMOS Tech
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A Study on Solid Phase Reactions of Ni and Pt on Si-Ge Alloys as Contacts to Ultra-Shallow P+N Junctions for CMOS Technology Nodes Beyond 70nm Jing Liu, Hongxiang Mo, Mehmet C. Öztürk Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695-7920, U.S.A. ABSTRACT Recently, selectively deposited SiGeB alloys have been proposed to form ultra-shallow source/drain junctions for 35-70 nm CMOS. The technology provides super-abrupt junctions with above equilibrium dopant activation at temperatures lower than 800ºC. In addition to their low resistivities, the lower bandgap of SiGeB provides the potential advantage of reducing the Schottky barrier height and therefore, the junction contact resistance. This is a critical concern for future CMOS technology nodes since the contact resistance will dominate the MOSFET series resistance unless new technologies yielding contact resistivities near 10-8 Ω-cm2 are developed. This paper examines the solid phase reactions of Ni and Pt with SiGeB alloys in order to form self-aligned low resistivity contacts. The results show that both Ni and Pt can form germanosilicides with low sheet resistances. Furthermore, both metals can form self-aligned contacts with a contact resistivity near 10-8 Ω-cm2. INTRODUCTION One of the factors limiting the MOSFET performance is source/drain junction series resistance. The series resistance of a typical junction consists of the spreading, accumulation, and the bulk components as well as the contact resistance between the silicide and the junction. As device dimensions are scaled below the 70 nm node, it is known that the contact resistance will dominate the junction series resistance unless new contact technologies are developed. According to the 1999 International Technology Roadmap for Semiconductors (ITRS) [1], contact resistivities as low as 1×10-8 Ω-cm2 will be required for technology nodes below 70 nm. For implanted junctions with silicide contacts, it is well understood that 10-7 Ω-cm2 is about the lowest contact resistivity achievable. This limit is set by two factors. First, the barrier height is determined by the Fermi level positioned near the silicon mid-gap for conventional silicides. Second, the electrically active doping concentration at the silicide/junction interface is limited by the solid solubility of the dopant. To satisfy the contact resistivity requirements of the ITRS, new junction and contact formation technologies with above-equilibrium dopant activation and smaller metal/semiconductor barrier heights will be needed. Recently, this laboratory has demonstrated a new ultra shallow junction technology capable of meeting the ITRS requirements for sub-70nm CMOS technology nodes [2]. In this technology, junctions are formed by low temperature (500oC) selective deposition of SiGeB alloys in the source/drain areas recessed by isotopic etching to the desired junction depth. By compensating the strain in the SiGe alloy using large concentrations of boron, above equilibrium boron activation is ach
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