Effects of post deposition annealing atmosphere on interfacial and electrical properties of HfO2/Ge3N4 gate stacks

Abstract

Effects of post deposition annealing (PDA) atmosphere, including oxygen (O2) gas and forming gas (FG), on interfacial and electrical properties of a HfO2 gate dielectric on nitrided Ge are analyzed. Experiments to study the dielectric morphology, interface quality, and chemical composition of HfO2/Ge3N4/Ge devices were carried out using X-ray diffraction, high-resolution transmission electron microscopy (HRTEM) imaging, and X-ray photoelectron spectroscopy (XPS) measurements, respectively. The XPS study confirmed that O2 PDA effectively improves the HfO2 film stoichiometry, and the stability of the interface between HfO2/Ge3N4/Ge stacks is enhanced. Further, HRTEM images showed that the interface between HfO2/Ge3N4/Ge stacks for O2-annealed devices was smooth, uniform, and flat. The experimental results for devices annealed in O2 at 500 °C exhibited improved interfacial and electrical characteristics, such as a high dielectric constant of ~19.50; high capacitance, 1.24 nF, low equivalent oxide thickness, 1.74 nm; interface trap density, 2.18 × 1011 cm−2 eV−1; oxide charges, 2.50 × 1012 cm−2; and gate leakage currents in the order nA of 0.5 × 10−9 A/cm2, as compared with FG annealing devices. The Fowler−Nordheim tunneling current conduction mechanism was also verified. Therefore, these results are evidence that the O2 PDA process improves the interfacial and electrical properties of HfO2/Ge3N4/Ge metal-oxide-semiconductor (MOS) devices as compared with FG annealing, which is important for future Ge-based complementary MOS device performance and reliability.