Phase-controlled molybdenum dioxide electrodes by RF reactive magnetron sputtering for achieving high-k rutile TiO2 dielectric

Abstract

Molybdenum dioxide (MoO2) has recently garnered attention as a promising oxide electrode for next-generation dynamic random-access memory capacitors owing to its high work function, low resistivity, and good thermal stability. The formation of pure, reliable MoO2 films is a significant challenge because of their higher formation energy than that of non-conductive orthorhombic molybdenum trioxide (MoO3). Herein, we investigated the controlled growth of MoO2 films by manipulating the process pressure and oxygen-to-argon (O2/Ar) ratio using radio frequency reactive magnetron sputtering. By increasing the O2/Ar ratio at a fixed process pressure (pp), sputtered MoOx films were fabricated as metallic Mo, monoclinic MoO2, and orthorhombic MoO3. The MoO2 film with Mo/O atomic ratio of 0.5 was achieved in the narrow process window of O2/Ar ratio of 0.22 and pp = 3 mtorr. The MoO2 films exhibited a smooth surface morphology with a root mean square roughness of 0.34–0.68 nm. The resistivity of MoO2 film was 972 μΩ cm, which was decreased to 374–524 μΩ cm by rapid thermal annealing in N2 at 600 °C-800 °C. The phase-controlled MoO2 electrode led to the in-situ crystallization of high-k rutile TiO2 with a dielectric constant of 93 via local epitaxial growth. This might be attributed to the excellent coherence in the atomic arrangement and low lattice mismatch between the distorted rutile MoO2 (011) and rutile TiO2 (110) planes.