Amorphous IGZO GAA Nanosheet FETs Using Typical Channel Release

Abstract

The amorphous InGaZnO (a-IGZO) gate-all-around (GAA) nanosheet (NS) field-effect transistors (FETs) are demonstrated. All process temperatures are below $300~^{\circ }$ C, showing back-end-of-line (BEOL) compatibility. The channel release (CR) is achieved by reactive-ion etching (RIE) with extremely high etching selectivity of the SiN sacrificial layer (SL) over the a-IGZO channel. A novel composite field oxide (FOX) is exploited to form an etching stop layer and to avoid gate leakage. The gate stacks are deposited all-at-once using plasma-enhanced atomic layer deposition (PEALD) following the CR to achieve the GAA structure, which is confirmed by the energy-dispersive X-ray spectroscopy (EDS) mapping. The device with a gate length of 52 nm shows ${I}_{\text {off}} \lt 10^{-{7}} ~\mu $ A/ $\mu $ m (below detection limit), high ${I}_{\text {on}}$ / ${I}_{\text {off}} \gt 1.3\times 10^{{8}}$ , positive threshold voltage ( ${V}_{T}$ ) of 3.5 V, and a clear saturation region in the output characteristic. Moreover, a subthreshold swing (SS) as low as 67 mV/dec is achieved a transition with the gate length of 150 nm.