Contact properties of titanium nitride electrode in vertical channel-all-around indium–gallium–zinc–oxide transistors

Abstract

Source/drain contact resistance (R_SD) is a decider of device performance in nanoscale indium–gallium–zinc–oxide (IGZO) transistors, especially in the ones featuring a vertical channel. In this work, titanium nitride (TiN), prepared by magnetron sputtering (MS) and ion beam sputtering (IBS), is adopted as the S/D electrodes of vertical channel-all-around (VCAA) IGZO transistors, and the contact properties are revealed. Both MS-TiN and IBS-TiN form Schottky contacts on IGZO, strongly limiting the ON-state current (I_ON) of VCAA IGZO devices with a 50 nm gate length. Such Schottky contacts result from metal oxidation during the atomic layer deposition (ALD) process of IGZO. IBS-TiN/IGZO shows a lower R_SD of 7.41 × 10⁻² MΩ as compared to MS-TiN/IGZO with an R_SD of 2.15 MΩ. The two kinds of TiN have an almost equal work function (φ_WF) of around 4.7 eV, the lower R_SD of IBS-TiN/IGZO is derived from the reduced tunneling resistance rather than Schottky barrier resistance. IBS-TiN appears denser with no detectable intergranular porosity whereas MS-TiN presents a typical microstructure comprising coarse and columnar grains with visible intercolumnar porosities, making IBS-TiN more robust against oxidation than MS-TiN. Also, the higher N/Ti ratio in IBS-TiN strengthens its antioxidation characteristic to some extent.