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

Y2O3/Ge gate stacks with ultrathin GeOx interlayer were fabricated by two-step rf sputtering using a Y2O3 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 (Dit) was characterized using a deep-level transient spectroscopy method with optimized injection pulse and quiescent reverse-bias voltages at each temperature. Dit 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.