Monolithic low-temperature fabrication of amorphous indium oxide thin-film transistors utilizing a selective hydrogen doping technique

Abstract

Selective doping is a key technology for integrated circuit (IC) fabrication since it enables ultrahigh density transistors with various electrical characteristics to be integrated on a single substrate. Also, for vertical IC integration, low-processing temperature compatibility is an essential feature since the annealing of additional ICs fabricated on top should not compromise the characteristics of underlying ICs. For amorphous oxide semiconductor (AOS) thin-films, which are actively being pursued for vertical integration, a selective doping process combined with a low temperature activation thermal annealing process has not been demonstrated. In this Letter, we demonstrate a low-temperature selective doping process that enables selective multi-level n-type doping of insulating amorphous In2O3 (a-In2O3) thin-films. By applying multiple H plasma processes on lithographically defined areas, a monolithic planar In2O3 inverter circuit was demonstrated. Also, the doping process was used to fabricate and demonstrate the operation of an In2O3 thin-film transistor with a 30 nm spaced channel, showing that our process may be used for back-end-of-line vertical integration of AOS devices.