Analysis of Channel-Length Dependence of Residual Hydrogen Diffusion From the Gate Insulator During Oxygen Annealing Treatment in IGZO TFTs

In previous research, it has been observed that the threshold voltage (V
$_{\text {TH}}$
) in IGZO TFTs will shift in the positive direction after the oxygen annealing treatment. However, in this study, IGZO TFTs with an etch stop layer (ESL) structure are annealed with oxygen at 250°C resulting in an abnormal VTH left-shift in short-channel devices. To better clarify the changes in the device characteristics, the output characteristics before and after annealing are compared. After the oxygen annealing treatment, the current-voltage (ID–V
$_{\text {D}}$
) output characteristics of the short-channel devices are enhanced, while those of the long-channel devices are degraded significantly, compared to the properties of the pristine devices. These trends in ID-VD curves can be further verified through capacitance-voltage (C-V) curves. The rising parasitic capacitance and C-V left shift imply the occurrence of hydrogen diffusion. Precisely speaking, it is the presence of residual hydrogen remaining in the gate insulator (GI) of Si3N4 that causes the changes in the device characteristics after oxygen annealing treatment. Subsequently, the physical models and the energy band diagrams are proposed to elucidate the channel-length-dependent behavior of residual hydrogen diffusion from the gate insulator after the oxygen annealing treatment.