NiSi formation in the Ni(Ti) /SiO 2 /Si System
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NiSi formation in the Ni(Ti) /SiO2/Si System R.T.P. Lee, D.Z. Chi*, and S.J. Chua Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602. ABSTRACT A NiSi silicide process employing a Ni(Ti) alloy has been investigated. It was experimentally demonstrated that a small amount of Ti in Ni could overcome the reaction-inhibiting effect of an interfacial oxide layer on Si. Ti in the deposited Nil film reacts with the interfacial oxide, yielding an altered oxide layer, which acts as a Ni-permeable diffusion membrane during silicidation. Good diode characteristics were obtained from p+/n silicided Ni(Ti)-diodes with an initial interfacial oxide. It is believed that the ability to form silicide effectively in the presence of a native oxide will greatly relieve constraints on processing conditions and significantly enhance manufacturing yield. INTRODUCTION The use of metallic silicides to reduce the gate and source/drain contact resistance is crucial in achieving high-speed device operation in advanced complementary metal-oxide-semiconductor (CMOS) devices. Recently NiSi has been shown to be an attractive alternative to currently used silicides, i.e., TiSi2 and CoSi2, for future 0.1 and sub-0.1 µm generation CMOS devices due to its high conductivity, large processing window, low Si consumption, and ability to maintain low resistivity even for linewidths down to 0.1µm [1]-[3]. However, there are several difficulties in implementing NiSi, including the sensitivity of NiSi formation to surface contaminants (e.g., residual interfacial oxide), which can lead to a rough interface and higher diode leakage on shallow junctions [4]. It has been shown that, like CoSi2, the formation of NiSi is substantially suppressed or even completely inhibited if a thin interfacial oxide is present [5]. For example, it was reported that the presence of a thin native oxide could effectively delay the formation of Nisilicide up to 800 oC [6]. In this paper, we present experimental results that show the dramatic effect of a small amount of Ti on NiSi formation in a Ni(Ti)/SiO2/Si system. EXPERIMENTAL p-type 10-15 Ω-cm (100)Si wafers were used in this study. The wafers were cleaned using standard RCA cleaning followed by dilute HF dip. A thin layer of silicon oxide (∼ 12 -13 Å thick) was grown on some of the wafers by immersing these wafers in boiling HCl/H2O2/H2O (3/1/1) for 10 min (Shiraki clean) [7]. Pure Ni and Ni(Ti)-alloy films of thickness ∼ 30 nm were then deposited on all wafers by magnetron sputtering. Ni(Ti)-alloy films were deposited by cosputtering of Ni and Ti . The concentration of Ti equals to 5 at. % in the Ni(Ti)-alloy films determined by Rutherford back scattering (RBS). All samples were then subjected to rapid thermal annealing (RTA) in nitrogen ambient for 60s. Phase identification was carried out using X-ray diffraction (XRD) and interdiffusion between layers was monitored by cross-section transmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS). *Email: [email protected]
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