Discovering the Impact of Cooling Scheme During Annealing: A New Knob for Achieving Thermally Stable IGZO FETs

To improve the thermal stability of indium-gallium-zinc-oxide (IGZO) field-effect transistors (FETs) in the oxygen-deficient environment, we examined the different annealing schemes with temperatures up to 450 °C. Our study revealed that the performance of IGZO FETs is not solely affected by the annealing temperature but also strongly influenced by the cooling scheme. Oxygen vacancies (VO)generated at high temperatures can remain at a high concentration, while VO can be gradually reduced with the slow cooling scheme. Additionally, we analyzed the impacts of downscaling the channel thickness (tch)on the thermal stability of IGZO FETs, observing that a thin IGZO channel leads to the positive threshold voltage (Vₜₕ)but suffers from more severe degradation in electrical performance and reliability. Based on the slow cooling scheme and proper selection of tch, a near-zero Vth and a relatively low subthreshold swing (SS) of 150 mV/dec of IGZO FETs with a channel length scaled to 100 nm are achieved after undergoing a high annealing temperature of 450 °C. Our discovery brings new possibilities for device fabrication and optimization for the advanced IGZO FETs.