Schottky-barrier height tuning using dopant segregation in Schottky-barrier MOSFETs on fully-depleted SOI
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0913-D01-07
Schottky-Barrier Height Tuning Using Dopant Segregation in Schottky-Barrier MOSFETs on Fully-Depleted SOI Joachim Knoch, Min Zhang, Qing-Tai Zhao, and Siegfried Mantl Institute of Thin Films and Interfaces, ISG1, Research Center Juelich, Juelich, D-52425, Germany
ABSTRACT In this paper we demonstrate the use of dopant segregation during silicidation for reducing the effective potential barrier height in Schottky-barrier metal-oxide-semiconductor field-effect-transistors (SB-MOSFETs). N-type as well as p-type devices are fabricated with arsenic/boron implanted into the device’s source and drain regions prior to silicidation. During full nickel silicidation a highly doped interface layer is created due to dopants segregating at the silicide-silicon interface. This doped layer leads to an increased tunneling probability through the Schottky barrier and hence leads to significantly improved device characteristics. In addition, we show with simulations that employing ultrathin body (UTB) silicon-on-insulator and ultrathin gate oxides allows to further improve the device characteristics. INTRODUCTION Schottky-barrier metal-oxide-semiconductor field-effect transistors (SB-MOSFETs) have recently attracted a renewed interest as an alternative over conventional MOSFETs since they offer solutions for aggressively scaled devices related to the source and drain contacts [1,2]: Due to metallic contacts directly attached to the channel, SB-MOSFETs exhibit low extrinsic parasitic resistances, offer easy processing and allow for well-defined device geometries down to smallest dimensions. However, at a metal-semiconductor contact a SB always builds up which is usually much larger than a few k BT and hence limits the on-state performance and causes poor subthreshold behavior. Recently, dopant segregation (DS) during silicidation has been successfully used in n-type bulk SB-MOSFETs and a significant reduction of the effective Schottky-barrier height and hence a strong improvement of the electrical characteristics of SBMOSFETs could be achieved [3]. Here we will show that arsenic as well as boron segregation during silicidation can be used to strongly improve the electrical characteristics of both, n-type as well as p-type SB-MOSFETs on fully depleted SOI with fully nickel silicided source and drain contacts. A further increase of the on-state current can be achieved by employing ultrathin body (UTB) SOI and ultrathin gate oxides which leads to a better carrier injection through the SBs. EXPERIMENT Commercially available SOI wafers with a p-type doping of 1015 cm-3 were first thinned by a cycle of dry/wet thermal oxidation and diluted HF stripping to a thickness of 25nm. After a standard mesa isolation and RCA cleaning a ~3.5nm thick gate oxide is grown followed by the deposition of 200nm n-doped poly-silicon. Subsequently the poly-silicon gate is patterned using
reactive ion etching. At this point, source and drain areas of one part of the samples were implanted (Fig. 1 (a)) with arsenic and boron with an energy of 5keV
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