Design Principle of Channel Material for Oxide-Semiconductor Field-Effect Transistor with High Thermal Stability and High On-current by Fluorine Doping

We propose material design guideline of oxide semiconductor field-effect transistor (OS-FET) based on first-principles calculation, and experimentally demonstrate excellent FET characteristics for the first time. Fluorine-doped In-Ga-Zn-O (IGZO) channel OS-FET exhibits both high thermal stability (>400°C) and high on-current at optimum F doping concentration which are required for co-integration with Si-CMOS as BEOL transistor. Our calculation revealed that high thermal stability comes from the release of overstress in IGZO by substitution of O by F. On the other hand, overdose of F decreases on-current by forming electron traps of metal-metal bonds. Considering these two different mechanisms behind, we successfully propose a breakthrough concept to improve thermal stability of OS-FET without degradation of on-current. Our results pave a new way for realizing high-performance BEOL transistors for 3D-LSI application.