Reliability improvement of IGZO TFTs through hydrogen control in SiNx gate insulators via N2 and NO plasma treatments with low temperature annealing

This study presents a low-temperature hydrogen control strategy for improving the reliability of amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) by engineering hydrogen bonding configurations in plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiNx) gate insulators. Although PECVD SiNx is widely employed, its intrinsic Si–H and N–H bonds act as a hydrogen reservoir, leading to severe electrical instability under bias stress. To mitigate this issue, N 2 and nitric oxide (NO) plasma treatments were systematically applied for varying durations of 1, 3 and 5 min, followed by post-annealing in an oxygen ambient at 350–450°C. Fourier transform infrared spectroscopy (FTIR) analysis reveals that a 3 min plasma treatment combined with 450°C annealing most effectively suppresses hydrogen-related bonds. In particular, NO plasma exhibits superior capability for suppressing hydrogen-related bonding configurations due to the synergistic effects of ion bombardment and reactive oxygen species, which facilitate both bond dissociation and hydrogen out-diffusion. Furthermore, X-ray photoelectron spectroscopy (XPS) provides evidence of hydrogen-related defect suppression through the reduction of Si–OH species and reconstruction of the SiNx network removal mechanism through the significant suppression of Si–OH bonding, the enhancement of O–Si–N network formation, and the reduction of Si–Si related defect states, indicating substantial structural stabilization of the SiNx film. As a result, the interface trap density (D it ) is significantly reduced from 2.81 × 10 12 to 3.15 × 10 11 cm −2 eV −1 , indicating substantial interface quality improvement. The optimized devices demonstrate enhanced electrical performance, including a field-effect mobility of 12.11 cm 2 /V·s and a subthreshold swing of 0.468 V/dec. Moreover, the bias temperature stress (BTS)-induced threshold voltage shift is dramatically suppressed from 10 V to 1 V after 2700s stress, confirming improved operational stability. Secondary ion mass spectrometry (SIMS) further confirms the effectiveness of the combined plasma and annealing treatments, showing approximately 14% and 33% reductions in the average 1H secondary-ion intensity after N 2 and NO plasma treatments followed by 450°C O 2 annealing, respectively, relative to the as-deposited SiNx film. These results confirm that precise control of hydrogen bonding in SiNx plays a critical role in suppressing defect generation, thereby improving device performance and reliability in oxide TFTs.