Theoretical and Empirical Insight into Dopant, Mobility and Defect States in W Doped Amorphous In2 O3 for High-Performance Enhancement Mode BEOL Transistors

Abstract

Tungsten (W) doped amorphous In2 O3 (IWO) enable BEOL-compatible enhancement mode (E-mode) nFETs with record performance such as ION ~500μA/μm, ION/IOFF ratio~10⁹ and ideal SS ~60mV/dec. The critical role of tungsten (W) doping in amorphous In2 O3 (a-In2 O3) for IWO FET is explored and revealed here for the first time using first-principles simulation and experimentation. We show that 1% W is the optimal doping for controlling carrier concentration and achieving the highest mobility for high-performance E-mode IWO FETs. Higher W-O bond dissociation energy suppresses oxygen vacancy (VO), leading to improved thermal and threshold voltage (VTH) stability. A defect gap states model is proposed and their influence on FET operation is investigated. This work provides guidance on mitigation of defects and further improvement in FET performance and VTH stability.