Implementation of oxide vertical channel TFTs with sub-150 nm channel length using atomic-layer deposited IGZO active and HfO2 gate insulator

Abstract

We fabricated vertical channel thin film transistors (VTFTs) with a channel length of 130 nm using an ALD In–Ga–Zn–O (IGZO) active channel and high-k HfO2 gate insulator layers. Solution-processed SiO2 thin film, which exhibited an etch selectivity as high as 4.2 to drain electrode of indium-tin oxide, was introduced as a spacer material. For the formation of near-vertical sidewalls of the spacer patterns, the drain and spacer were successively patterned by means of two-step plasma etching technique using Ar/Cl2 and Ar/CF4 etch gas species, respectively. The SiO2 spacer showed smooth surface morphology (R q = 0.45 nm) and low leakage current component of 10–6 A cm−2 at 1 MV cm−1, which were suggested to be appropriate for working as spacer and back-channel. The fabricated VTFT showed sound transfer characteristics and negligible shifts in threshold voltage against the bias stresses of +5 and −5 V for 104 s, even though there was abnormal increase in off-currents under the positive-bias stress due to the interactions between hydrogen-related defects and carriers. Despite the technical limitations of patterning process, our fabricated prototype IGZO VTFTs showed good operation stability even with an ultra-short channel length of 130 nm, demonstrating the potential of ALD IGZO thin film as an alternative channel for highly-scaled electronic devices.