Atomic Layer Deposition of Metallic Molybdenum Dioxide Thin Films Enabling High‐ k Rutile Capacitors

ABSTRACT Molybdenum dioxide (MoO ₂ ) thin films have attracted considerable attention as electrode materials for high‐ k capacitors, such as those used in dynamic random‐access memory (DRAM) devices. Properties that make MoO ₂ highly attractive include high conductivity, high work function (> 5 eV), distorted rutile crystal structure, and chemical stability. However, currently, atomic layer deposition (ALD) of crystalline MoO ₂ is not possible without additional (post‐)deposition steps. In this work, the first direct ALD process for MoO ₂ thin films is presented using molybdenum(II) acetate dimer (Mo ₂ (OAc) ₄ ) and oxygen (O ₂ ) as precursors. Controlled growth was observed at 235°C–275°C, yielding crystalline MoO ₂ films with a distorted rutile (tugarinovite) crystal structure. The films were stoichiometric, exceptionally pure with ∼1 at.% total impurities, and highly conductive with a resistivity of 400 µΩ∙cm. Application potential of the process was demonstrated by depositing low temperature (150°C–275°C) high‐ k rutile titanium dioxide (TiO ₂ ) dielectric thin films and subsequently capacitor devices based on MoO ₂ electrodes. This work expands the selection of thin film materials deposited by ALD with MoO ₂ , enabling deposition of a full range of molybdenum oxides from MoO ₂ to MoO _x<3 to MoO ₃ .