Influence of Atomic Hydrogen on Nickel Silicide Formation
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Influence of Atomic Hydrogen on Nickel Silicide Formation A. Vengurlekar1, Satheesh Balasubramanian1, S. Ashok1, N. D. Theodore2 and D.Z. Chi3 1 Department of Engineering Science & Mechanics, Pennsylvania State University, University Park, Pennsylvania, PA 16802, U.S.A. 2 Motorola Inc., Advanced Products R&D Labs, Tempe, AZ 85284, U.S.A. 3 Institute of Materials Research and Engineering, 117602, Singapore. ABSTRACT Nickel monosilicide (NiSi) is a leading contender to replace the currently used class of silicides for contacts to the source, drain and gate regions in Complimentary Metal-OxideSemiconductor (CMOS) circuits. In this work, the effect of substrate hydrogenation by a hydrogen plasma treatment prior to nickel deposition and silicidation was studied. The sheet resistance of the silicide film shows a significant decrease under hydrogenation of the Si substrate prior to Ni evaporation/anneal for projected silicidation temperatures below 600 oC. Correspondingly, the Si region near the interface is decorated with defects. At higher silicidation temperatures, the sheet resistance rises along with greater in-diffusion of Ni into the hydrogenated Si samples. Secondary Ion Mass Spectrometry, Transmission Electron Microscopy and Hall effect measurements are used to characterize the samples.
INTRODUCTION Silicides are widely used in the Si microelectronics industry as contact materials to the source, drain and gate regions in CMOS circuits. Nickel Silicide (NiSi) is gaining attention as a replacement for the currently used class of silicides because of the advantages it offers in comparison to cobalt silicide and titanium silicide [1]. These advantages include a more optimal silicidation temperature, low sheet resistance, lower silicon consumption during silicidation, absence of narrow line effect and bridging failure, lower film stress and reduced dopant redistribution [2]. However, certain issues in nickel silicide still remain unresolved. These include oxidation of the nickel film during the silicidation process and large leakage currents of devices using NiSi as the contact material [3]. Sheet resistance is a particularly important parameter in applications where silicides are used. Lowering of the sheet resistance would be advantageous because as device dimensions are scaled down, the effects of parasitic resistance and capacitance become more pronounced, necessitating fabrication of low resistance contacts to ensure that the speed of the circuit is not limited by the RC time constant. Therefore, reduction of sheet resistance of the silicide film is an important challenge. Earlier attempts to tackle the problems of NiSi oxidation and to lower the sheet resistance included the use of Ti and TiN capping layers [3,4], hydrogen implantation into the evaporated Ni film [5] and evaporation of Ni alloyed with Pt [6]. The interaction of atomic hydrogen with crystalline defects in Si has been a subject of interest for over two decades [7] and is suffused with numerous phenomena and applications. In this paper, we
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