Interface Engineering for IGZO/Metal Contacts: Reducing Contact Resistivity with SiO2 Inter-Layers Using Cross-Bridge Kelvin Resistor Analysis

Abstract

Achieving low-resistance and stable metal contacts in Indium-Gallium-Zinc-Oxide (IGZO) semiconductors remains a critical challenge due to Fermi level pinning (FLP) at the metal/semiconductor interface. This study investigates the impact of metal work function and inter-layer engineering on the contact resistivity (Rc) of IGZO, using a Cross-Bridge Kelvin Resistor (CBKR) structure for precise electrical characterization. Work function measurements using ultraviolet photoelectron spectroscopy (UPS) indicated that Ti should exhibit lower contact resistivity than Mo based on ideal Schottky barrier height (SBH) calculations. However, experimental results revealed that Mo exhibited lower Rc than Ti, demonstrating that FLP, driven by metal-induced gap states (MIGS), significantly impacts IGZO/metal contact resistivity, overriding the expected Schottky barrier behavior. To mitigate FLP, an ultrathin PEALD SiO<inf>2</inf> inter-layer (0-1 nm) was introduced at the Mo/IGZO interface, acting as a tunneling dielectric barrier. Contact resistivity measurements revealed that Rc decreased with increasing SiO<inf>2</inf> thickness up to 0.75 nm, confirming that a thin inter-layer can effectively suppress MIGS and enhance charge injection. However, at 1 nm, Rc increased, likely due to excessive tunneling resistance. These findings highlight the importance of interfacial engineering in optimizing IGZO/metal contacts and demonstrate that a carefully tailored SiO<inf>2</inf> inter-layer can significantly improve contact performance and device reliability.