Investigation on characteristics of niobium nitride and molybdenum nitride gates on hafnium oxide gate dielectrics

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In this study, niobium nitride (NbNx) and molybdenum nitride (MoNx) thin films are deposited by magnetron sputtering on various thicknesses of HfO2 gate dielectrics (i.e., 2 nm, 4 nm, 6 nm, 8 nm, and 12 nm) to fabricate the metal/oxide/semiconductor capacitors. The incorporation of nitrogen into the NbNx and MoNx films is controlled by N2/(Ar+N2) flow ratios. The Nb/NbNx and Mo/MoNx gate stacks are deposited on HfO2, and followed by forming gas annealing (FGA) at 400oC for 30 min. The characteristics of Nb/NbNx and Mo/MoNx thin films deposited with various N2/(Ar+N2) flow ratios, before and after FGA, are examined. In addition, the effective work functions (Φm) of gate electrodes are also extracted from capacitance-voltage (C-V) curves to discuss the relation between material properties and the shift of Φm. The thicknesses and surface morphology of NbNx and MoNx films are determined by field emission scanning electron microscopy (FESEM). The crystal structure is identified by grazing incidence angle x-ray diffractometer (GIAXRD). The composition and chemical bonding of NbNx and MoNx films are tailored by X-ray photoelectron spectroscopy (XPS). For electrical properties, the resistivity is measured by four point probe, and C-V curves are obtained by using the LCR meter (Agilent E4980A) to extract the Φm. The SEM and GIAXRD results show that the morphology and crystal structure of NbNx and MoNx films exhibit a transition when the N2/(Ar+N2) flow ratio is more than 2%. The surface morphology changes from polyhedron to slab, and the phase changes from body-centered- cubic to face-centered- cubic structure. The NbNx structure is becoming nearly amorphous when the N2/(Ar+N2) flow ratio increases, whereas the MoNx structure shows increased crystallinity. Moreover, the resistivity of MoNx films, before and after FGA, is lower than that of NbNx films using the same deposition parameters. The results reveal that the Φm of NbNx films ranges from 3.83 eV to 4.17 eV, and that of MoNx films ranges from 4.58 eV to 5.23 eV. It suggests that the Φm can be modulated by the nitrogen content. Consequently, the NbNx and MoNx gate electrodes are promising for applications in n-channel and p-channel metal-oxide-semiconductor field-effect transistors, respectively.