Electrical profiles of ultra-low energy antimony implants in silicon
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Electrical profiles of ultra-low energy antimony implants in silicon T. Alzanki, R. Gwilliam, N. Emerson and B. J. Sealy Advanced Technology Institute, University of Surrey, Guildford, Surrey, GU2 7XH, UK E. Collart Applied Materials UK Ltd., Parametric and Conductive Implant Division, Foundry Lane, Horsham, W-Sussex, RH13 5PX, UK ABSTRACT A novel Differential Hall Effect technique is used to obtain doping profiles of 2keV implants of antimony in silicon at a depth resolution of 2nm. The electrical profiles are compared with atomic profiles determined from Secondary Ion Mass Spectroscopy (SIMS) measurements. We demonstrate good consistency between the two profiling techniques and confirm that the SIMS profiles can be used to identify the junction depth. The profiles show that antimony does not diffuse significantly for annealing temperatures below 800oC. INTRODUCTION Since the 1970’s, silicon CMOS gate dimensions have been reduced from about 10 microns to sub-0.1µm. As devices shrink, it is essential to implement ultra shallow source and drain junctions to overcome short channel effects. Thus very short gate length transistors with shallow source/drain extension junctions and small gate overlap have been reported by many [15]. The junction depth is mainly controlled by the ion energy assuming that diffusion during annealing is negligible. Thus antimony is a suitable ion species for the fabrication of shallow ntype extensions because of its heavy mass and low diffusivity [6]. However, there are reports that the equilibrium solubility limit is too low at 1×1019cm-3 at 850oC and 2×1019cm-3 at 1000oC [6], but more recently a value of 4.5×1020 cm-3 has been reported, which is more acceptable [7]. Few details of the electrical characteristics of low energy antimony implants have been published and most papers concentrate on sheet resistance measurements [8], although some have performed Hall effect profiling [9]. In contrast, in this paper, we concentrate on the determination of the carrier concentration profiles of 2keV antimony implants and compare these with atomic profiles measured by SIMS. EXPERIMENTAL P-type Si wafers of diameter 200mm with a bulk resistivity of 2-10 Ω.cm were implanted at RT with 2 keV antimony at a dose of 1×1015 cm-2. A second implant of antimony 13 -2 (30keV at dose of 2×10 Sb+cm ) is used to extend the profile and move the n+p junction deeper within the material and away from the primary shallow implant which is to be measured. The tilt and twist angles for implantation were 7o and 22o respectively. The 2keV implants were carried out first, using an Applied Materials xRLEAP implanter, whilst the secondary implants at 30keV were performed on a 200 kV Danfysik 1090 accelerator. After implantation the wafers were annealed at temperatures from 600oC to 1100oC for annealing times of 10s to 1 hour. The annealing was performed using a Process Products Corporation RTP system with flowing
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nitrogen ambient. Following annealing, cloverleaf patterns were printed on the samples using photo
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