Optimizing ferroelectric performance of HZO-based MFIS capacitors through controlled H2 plasma treatment of the SiO2 interfacial layer

The effects of ex situ H 2 plasma treatment of the SiO 2 interfacial layer (IL) on the ferroelectric properties of Al/Al 2 O 3 /Hf 0.5 Zr 0.5 O 2 (HZO)/SiO 2 /p-Si metal–ferroelectric–insulator–semiconductor (MFIS) capacitors were investigated. The SiO 2 IL was exposed to H 2 plasma for 0–300 s prior to HZO deposition. The hysteresis loop height (2P r = P max − P min ) exhibited a non-monotonic dependence on treatment time, peaking at 37 μC/cm 2 for the sample treated for 60 s (H60) compared with 18 μC/cm 2 for the untreated one (H0). Positive-up–negative-down (PUND) measurements confirmed genuine switching, with the switching polarization ΔP peaking at 10.4 μC/cm 2 for H60. The optimized H60 capacitor showed a low leakage current density of approximately 10 −6 A/cm 2 at ±5 V, a suppressed interface trap conductance response, and an enhanced endurance of 10 6 cycles. These results indicate that moderate hydrogen exposure passivates interfacial defects and supplies oxygen vacancies that stabilize the polar orthorhombic phase. Conversely, prolonged exposure of 300 s degrades the interfacial region and injects excess hydrogen into the HZO film, driving a transition to the non-polar monoclinic phase and a loss of ferroelectricity. Grazing-incidence X-ray diffraction and X-ray photoelectron spectroscopy corroborate this mechanism, revealing monoclinic phase growth and increased oxygen-deficient fraction in the overtreated film. These findings establish a controlled H 2 plasma dose window for high-performance HZO-based MFIS devices.