Investigating Residual Hydrogen Diffusing from Bottom Gate Insulators in IGZO TFTs during Oxygen Annealing with Capacitance-Voltage Measurements

Po-Yu Yen^1*, Kuan-Ju Zhou¹, Kui-You Shao¹, Po-Yi Lee¹, Tzu-Hsuan Juan¹, Yu Shan Lin¹, Ting-Chang Chang¹

¹Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan

* Presenter:Po-Yu Yen, email:boydyenyes@gmail.com

In prior investigations, it was noted that the threshold voltage (Vth) of IGZO TFTs tends to shift positively after oxygen annealing treatment. However, in our work, IGZO TFTs with an etch stop layer (ESL) structure are subjected to oxygen annealing at 250 ℃, resulting in an unexpected leftward shift in Vth for short-channel devices. To provide a clearer understanding of the alterations in device characteristics, output characteristics are compared before and after annealing. After the oxygen annealing treatment, the current-voltage (Id–Vd) output characteristics of short-channel devices showed improvement than that of before oxygen annealing, while those of long-channel devices deteriorated significantly compared to the properties of pristine devices. The trends in the Id–Vd curves are further clarified through capacitance-voltage (C–V) curves. The increase in parasitic capacitance and the leftward shift in the C–V curves suggest the diffusion of hydrogen. Specifically, the presence of residual hydrogen within the gate insulator, SiNx, is responsible for the changes in device characteristics after oxygen annealing treatment. Subsequently, physical models and energy band diagrams are proposed to elucidate the channel-length-dependent behavior of residual hydrogen diffusion from the gate insulator after oxygen annealing treatment.

Keywords: Oxygen annealing, IGZO TFTs, Residual hydrogen, Gate insulator