Effects of the Oxygen Content of a-IGZO Field-Effect Transistors on Their Density of States and Dopant Concentration Lateral Profile Regarding Oxygen Scavenging

Abstract

The oxygen flow rate (OFR) during sputtering deposition of amorphous indium-gallium-zinc-oxide (a-IGZO) was systematically adjusted to modulate the oxygen vacancy (V-O) concentration in the channel, yielding O-poor, O-mid, and O-rich FETs. Under identical source/drain metal and annealing conditions, a pronounced oxygen scavenging (OS) effect was observed at lower OFRs, resulting in significant source/drain contact resistance (R-SD) reduction due to the lowered V-O formation energy. However, while reduced oxygen content effectively suppressed R-SD, it simultaneously induced undesirable threshold voltage (VT) shifts caused by OS-driven carrier diffusion from the source/drain regions into the channel. Consequently, a clear trade-off between R-SD reduction and VT stability was identified, wherein lower OFR enhanced R(SD )suppression at the expense of VT controllability. In contrast, higher OFR stabilized VT with limited R-SD improvement. An optimal OFR was therefore proposed by decoupling the OS contributions to R-SD and V-T. In addition, the V-T shift increased with decreasing channel length, and this tendency was more evident at lower OFRs.