Hydrogen Plasma Treatment for Improving Reliability of In-Ga-Zn-O Transistors Without Side Effects Through Post-Annealing Process

In this work, a novel hydrogen process is proposed to enhance the stability of IGZO transistors without side effects such as defect generation or negative threshold voltage (V_TH) shift. Conventional hydrogen treatments on IGZO transistors, including thermal annealing and plasma, typically resulted in excess hydrogen incorporation, leading to unstable states like M─OH bonds and hydrons, which degrade electrical stability. This approach integrates a post-annealing process step following plasma treatment, eliminating undesired hydrogen-related states while preserving only beneficial and stable hydrogen bonds. The hydroxyl radicals formed during hydrogen plasma are converted into highly reactive oxygen radicals in an oxygen-rich environment. These oxygen radicals subsequently passivate oxygen vacancies to form stable M─O bonds. Compared to bare devices, interface/bulk trap densities are reduced by 90% and 86%, respectively, after the hydrogen process; this is attributed to the effective removal of deep-level oxygen defects and the formation of stable M─O bonds during the post-annealing process. As a result, IGZO transistors treated with this hydrogen process showed a significant reduction in ∆V_TH under positive gate-bias and negative gate-bias illumination stresses by 83% and 62%, respectively, along with high field-effect mobility (15.14 ± 0.39 cm² V s⁻¹), subthreshold slope (90 ± 5.9 mV dec⁻¹), and I_on/I_off ratio (>10⁷).