Low-temperature fabrication of Y₂O₃/Ge gate stacks with ultrathin GeO_x interlayer and low interface states density characterized by a reliable deep-level transient spectroscopy method

Y₂O₃/Ge gate stacks with ultrathin GeO_x interlayer were fabricated by two-step rf sputtering using a Y₂O ₃ target followed by a vacuum-annealing, which were carried out in the same chamber without vacuum breaking. TiN-gate Ge metal-insulator- semiconductor (MIS) capacitors were fabricated with equivalent oxide thicknesses in the range of 2.1-2.3 nm. The highest temperature was 400 °C for the entire fabrication process. Interface states density (D_it) was characterized using a deep-level transient spectroscopy method with optimized injection pulse and quiescent reverse-bias voltages at each temperature. D _it values were approximately 4 × 10¹³, 5 × 10¹¹, and 3 × 10¹² cm^{- 2} eV^{- 1} at energy positions around valence band, mid-gap, and conduction band, respectively. The slow trap contribution was also small in the upper half of the band-gap, implying a potential application of the Y₂O₃/Ge gate stack to the fabrication of high-performance Ge-n-MIS field effect transistors.