Growth and Characterization of Erbium Silicides Synthesized by Metal Vapor Vacuum Arc Ion Implantation
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Growth and Characterization of Erbium Silicides Synthesized by Metal Vapor Vacuum Arc Ion Implantation X. W. Zhang, W. Y. Cheung, S. P. Wong Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, N. T., Hong Kong, P. R. China ABSTRACT Erbium atoms were implanted into p-type Si (111) wafers at an extraction voltage of 60 kV to doses ranging from 5×1016 to 2×1017 cm-2 using a metal vapour vacuum arc (MEVVA) ion source. The implantation was performed with beam current densities from 3 to 26 µA/cm2 corresponding to substrate temperatures ranging from 85 to 245oC. The characterization of the as-implanted and annealed samples was performed using Rutherford backscattering spectrometry, atomic force microscopy and x-ray diffraction. To determine the sputtering yield, masked implantation experiments were performed so that the thickness of the sputtered layer at different substrate temperatures can be obtained directly by an α-step surface profiler. The results showed that ErSi2-x was directly formed by MEVVA implantation when the substrate temperature was higher than about 160oC. The effects of the implant dose and the beam current density on the retained dose, the sputtering yield and the surface morphology of the implanted samples were also studied. INTRODUCTION Erbium silicide has attracted considerable attention because of its potential applications in interesting new devices such as metal base transistors or tunable infrared detectors, and in conventional microelectronics technology as an ohmic or rectifying contact. Recently, various techniques [1-6] including solid phase epitaxy, molecular beam epitaxy, reactive deposition epitaxy and ion beam synthesis (IBS) have been used to synthesize ErSi2-x. Among these methods, the IBS method has some advantages such as the ease of control of the implant dose, the high reproducibility of the process, and the ability to directly form a buried layer. For growth of erbium silicide, the IBS method has the additional advantage that it can avoid the problem caused by the very high chemically reactivity of erbium. One major difficulty of the IBS technique is the high dose required to form a continuous silicide layer. However, the high dose problem is solved by using a metal vapor vacuum arc (MEVVA) ion source developed by Brown et al. in 1985 [7]. The MEVVA source can provide high current ion beams up to 120 µA/cm2 for almost all the metal ions. Such a high beam current capability makes it attractive for use in the IBS of metal silicides. In fact, it has been reported that good quality metal silicide layers have been successfully synthesized using the MEVVA ion source [8, 9]. In this paper, we shall present the preliminary results of our study on the formation of erbium silicide layers by IBS using a MEVVA ion source. In addition, we have also studied the effect of beam current density on the sputtering yield and surface morphology of the erbium silicide layers. EXPERIMENTAL DETAILS High dose Er implantation into p-Si (111) wafers of 10-20 Ω cm was performed
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