Impact of N₂O Plasma Reactant on PEALD-SiO₂ Insulator for Remarkably Reliable ALD-Oxide Semiconductor TFTs

We studied nitrogen (N) incorporation effects on the electrical characteristics of SiO ₂ fabricated by plasma-enhanced atomic layer deposition (PEALD). To determine whether N could be incorporated into the SiO ₂ , nitrous oxide (N ₂ O) plasma with different plasma powers (100, 150, and 200 W) was used during the SiO ₂ deposition, and the film properties were compared with SiO ₂ fabricated using a conventional oxygen (O ₂ ) plasma reactant. Compared to the O ₂ plasma reactant, the hard breakdown is improved by 27.5% as N ₂ O plasma power increases up to 150 W, whereas it is degraded at a N ₂ O plasma power of 200 W. These results are found to describe the relationship between the N content and film properties. The N content in the SiO ₂ films fabricated using increasing N ₂ O plasma power of 100, 150, and 200 W gradually increased by 0.2%, 0.4%, and 0.5%, respectively. However, the N ₂ O plasma power of 200 W results in increased O deficient Si bonding. To investigate the effects of continuous plasma exposure at the bottom layer during the SiO ₂ deposition, we fabricated indium–zinc oxide (IZO) top-gate bottom-contact (TG-BC) thin-film transistors (TFTs) using the SiO ₂ as a gate insulator (G.I). Compared to the O ₂ plasma, the IZO TFTs using N ₂ O plasma reactant during the G.I deposition show stable transfer characteristics. The IZO TFT using N ₂ O plasma with 150-W power during the G.I deposition shows the optimal positive/negative bias temperature stress (P/NBTS) results, with the threshold voltage ( $V_{\mathbf {TH}}$ ) variations of 0.0 and −0.3 V, respectively.