Doping and Mobility Profiles in Defect-Engineered Ultra-shallow Junctions: Bulk and SOI
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Doping and Mobility Profiles in Defect-Engineered Ultra-shallow Junctions: Bulk and SOI. A. J. Smith(1), B. Colombeau(1), R. Gwilliam(1), E. Collart(2), N.E.B. Cowern(1), B. J. Sealy(1). Advanced Technology Institute, Surrey University, Guildford, GU2 7XH, U.K. (2) Applied Materials UK Ltd, Parametric and Conductive Implant Division, Horsham, RH13 5PX, UK (1)
ABSTRACT Silicon on insulator (SOI - Smartcut®) wafers were implanted with 1MeV and 300keV silicon ions to doses of 3.8x1015 cm-2 and 3x1014 cm-2, respectively, in order to modify the vacancy concentration in a controlled way. Boron was then implanted at 2keV to a dose of 1x1015 cm-2 into the near-surface part of the vacancy-engineered region. Atomic profiles were determined using SIMS and electrical profiles were measured using a novel Differential Hall Effect (DHE) technique, which enables profiling of electrically active dopants with a nanometer depth resolution. The electrical profiles provide pairs of carrier concentration and mobility values as a function of depth. The buried oxide (BOX) is proven to restrict the back diffusing interstitials positioned below the BOX from entering the silicon top layer and interacting with the boron profile. Also an increase of ∼50% in boron activation is achieved when a co-implant is used. However, SOI shows a reduced degree of activation when compared to bulk silicon, with or without a co-implant. INTRODUCTION The use of high-energy co-implants has been shown to create a net increase in vacancies in the near surface region [1]. The increase in vacancies within this area reduces Transient Enhanced Diffusion (TED) [2], Boron Enhanced Diffusion (BED) [3] and increases electrical activation [4]. Most work so far has been performed in bulk silicon. Nejim et al. [5] recently showed that a 10keV boron implant exhibiting TED can be quenched to a near as-implanted profile by using a 1MeV, 1x1016 cm-2, Si co-implant. As the energy of the B implant is reduced the effect of the co-implant decreases, so that no distinguishable effect is observed for a 2keV B implant. However, Shao et al. [6] used a 500keV Si co-implant on a similar 2keV boron implant and a slight reduction in enhanced diffusion was observed. This suggests that there may be an optimal co-implant for reducing diffusion and enhancing activation for all types of boron implants. As B ion energies continue to decrease there are more stringent requirements on the percentage of activation, which pushes the boundaries of solid solubility in fulfilment of the future requirements of CMOS devices. Point defect engineering can hold the key to creating shallow p-type layers without pre-amorphising, conforming to the guidelines set by the international technology roadmap for semiconductors (ITRS). Silicon On Insulator (SOI) has been used in the past for point defect engineering, most recently by Nejim et al. [5] and Shao et. al. [7]. SOI has an advantage of a buried amorphous insulating layer which can separate the two point defect regions created by a high-energy Si co-im
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