Atomic-layer-deposited (ALD) Al_2O_3passivation dependent interface chemistry,band alignment and electrical properties of HfYO/Si gate stacks

In this work, the effects of atomic-layer-deposited (ALD) Al₂O₃ passivation layers with different thicknesses on the interface chemistry and electrical properties of sputtering-derived HfYO gate dielectrics on Si substrates have been investigated. The results of electrical measurements and X-ray photoelectron sepectroscopy (XPS) showed that 1-nm-thick Al₂O₃ passivation layer is optimized to obtain excellent electrical and interfacial properties for HfYO/Si gate stack. Then, the metal-oxide-semiconductor capacitors with HfYO/1-nm Al₂O₃/Si/Al gate stack were fabricated and annealed at different temperatures in forming gas (95% N₂+5% H₂). Capacitance-voltage (C-V) and current density-voltage (J-V) characteristics showed that the 250 °C-annealed HYO high-k gate dielectric thin film demonstrated the lowest border trapped oxide charge density (-3.3 × 10¹⁰ cm⁻²), smallest gate-leakage current (2.45 × 10^-6 A/cm² at 2 V) compared with other samples. Moreover, the annealing temperature dependent leakage current conduction mechanism for Al/HfYO/Al₂O₃/Si/Al MOS capacitor has been investigated systematically. Detailed electrical measurements reveal that Poole-Frenkle emission is the main dominant emission in the region of low and medium electric fields while direct tunneling is dominant conduction mechanism at high electric fields.