High-Performance Thin-Film Transistor with Atomic Layer Deposition (ALD)-Derived Indium–Gallium Oxide Channel for Back-End-of-Line Compatible Transistor Applications: Cation Combinatorial Approach

In this paper, the feasibility of an indium–gallium oxide (In2(1‑x)Ga2x O y ) film through combinatorial atomic layer deposition (ALD) as an alternative channel material for back-end-of-line (BEOL) compatible transistor applications is studied. The microstructure of random polycrystalline In2O y with a bixbyite structure was converted to the amorphous phase of In2(1–x)Ga2x O y film under thermal annealing at 400 °C when the fraction of Ga is ≥29 at. %. In contrast, the enhancement in the orientation of the (222) face and subsequent grain size was observed for the In1.60Ga0.40O y film with the intermediate Ga fraction of 20 at. %. The suitability as a channel layer was tested on the 10-nm-thick HfO2 gate oxide where the natural length was designed to meet the requirement of short channel devices with a smaller gate length (108, which would be applicable to the logic devices such as peripheral circuit of heterogeneous DRAM. The in-depth origin for this promising performance was discussed in detail, based on physical, optical, and chemical analysis.