Mitigating hydrogen-related instabilities in oxide thin-film transistor via nitrogen-engineered passivation layer for thermal stability

Abstract

In conventional dynamic random-access memory (DRAM) processes, hydrogen-rich SiH₄-based dielectrics such as SiO₂, SiN_X, or SiCOH are widely used for defect passivation and performance enhancement in silicon-based cell transistors. However, when applied to amorphous indium-gallium-zinc oxide (a-IGZO) channel, hydrogen induces anomalous, non-monotonic V_th shifts and degrades reliability by weakening the channel’s bonding structure. Here, a novel technique is reported using the SiON and nitrogen dioxide plasma treatment layer (SNL) for the passivation layer. The SNL technique reduces hydrogen incorporation in the passivation layer and impedes hydrogen diffusion pathways through nitrogen doping within the channel layer simultaneously. As a result, compared to conventional thin-film transistors (TFTs), the SNL TFTs exhibited significantly improved breakdown voltages (from 90 to 177 V), reduced threshold voltage shifts under positive/negative bias temperature and illumination stress (PBTS/NBTiS) conditions (from −177 to −18 mV, and from −9.36 to −4.64 V) for 11 h. They markedly suppressed transient current deviation during transient current stress (TCS) measurements—from 1.42 % to 0.23 % after high-current stress and from 1.27 % to 0.10 % after low-current stress—indicating reduced hydrogen-related shallow trapping. Furthermore, the SNL structure effectively suppresses hydrogen-induced channel edge encroachment (ΔL) due to thermal stress, limiting the increase to only 0.11 μm (i.e., from 1.81 μm to 1.92 μm).