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

Abstract

We studied nitrogen (N) incorporation effects on the electrical characteristics of SiO2 fabricated by plasma-enhanced atomic layer deposition (PEALD). To determine whether N could be incorporated into the SiO2, nitrous oxide (N2O) 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 N2O plasma power increases up to 150 W, whereas it is degraded at a N2O 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 N2O plasma power of 100, 150, and 200 W gradually increased by 0.2%, 0.4%, and 0.5%, respectively. However, the N2O 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 O2 plasma, the IZO TFTs using N2O plasma reactant during the G.I deposition show stable transfer characteristics. The IZO TFT using N2O 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 (VTH) variations of 0.0 and -0.3 V, respectively.