Modification of Electrode-Etchant for Sidewall Profile Control and Reduced Back-Channel Corrosion of Inverted-Staggered Metal-Oxide TFTs

Abstract

For metal-oxide thin-film transistors (TFTs), the inverted staggered structure is hard to attain, given the sensitivity of metal-oxides to etchants used to define shapes of the source and drain electrodes. Here we present the development of a hydrogen peroxide (H2O2)-based (H2O, H2O2 and ammonium + azole) source/drain electrode wet-etchant, modified for reduced backchannel corrosion and metal electrode sidewall profile control. Diluting the etchant with ammonium decreases its acidity (from pH ∼3 to ∼5), resulting in decreased electrode etch rate and reduced metal-oxide backchannel corrosion as confirmed by corrosion potential measurements and X-ray photoelectron spectroscopy. However, slow etch rate yields a <20° non-uniform tapered electrode sidewall profile, which necessitates addition of an azole as an electrode sidewall corrosion inhibitor. The azole inhibits lateral corrosion, thereby achieving a uniform vertical etch, as it gets adsorbed at the metal sidewalls due to its chelating effect with metal ions that accumulate at the sidewalls during dip (immersion) etch. Metal oxide (amorphous-indium-gallium-zinc-oxide) TFTs fabricated by using the H2O2-based etchant exhibited turn-on voltages close to zero volts and subthreshold voltage slopes of ∼370 mV/dec.