Study of Contact Resistance Components in Short-Channel Indium-Gallium-Zinc-Oxide Transistor

Contact resistance (R-c) is a major limitation to the scaling of amorphous indium-gallium-zinc-oxide (a-IGZO) transistors, and it has not been thoroughly investigated on devices with sub-100-nm dimensions. In this work, we characterize back-gated a-IGZO transistors with scaled channel length down to 45 nm, showing that the ON-current is strongly limited by R-c in short-channel devices. As a case study to investigate the origins of R-c, we compare physical vapor deposited (PVD) TiN and atomic layer deposited (ALD) TiN as the contact metal, revealing that R-c in ALD-TiN/a-IGZO devices is three times higher than in PVD-TiN/a-IGZO devices. By investigating multiple components of the contact resistance, we demonstrate that while both contacts have similar Schottky barrier heights (SBHs), a thicker oxide interfacial layer between ALD-TiN and IGZO may be one cause for the higher R-c. We also investigate that reduced hydrogen-induced doping can lead to an increase in contact resistance.