Atomic layer deposition of MoO2 using a tetravalent precursor for template-driven rutile TiO2 growth in DRAM capacitors

Abstract

To achieve high capacitance in next-generation dynamic random-access memory (DRAM) capacitors, rutile TiO2 with a high dielectric constant is a promising dielectric material. However, TiO2 films deposited through atomic layer deposition (ALD) typically form the anatase phase with a lower dielectric constant. To promote rutile phase growth, conductive oxides such as RuO2, SnO2, and MoO2 have been explored as template layers. Among them, MoO2 is particularly attractive because of its high work function and excellent chemical stability. Conventional ALD of molybdenum oxides typically yields the thermodynamically stable MoO3 phase rather than MoO2. In this study, MoO2 thin films were successfully deposited through ALD using a tetravalent molybdenum precursor, bis (isopropylcyclopentadienyl)molybdenum dihydride, and ozone as oxidants. The process exhibited self-limiting growth behavior and yielded high-quality MoO2 films without additional doping or post-reduction steps. After annealing at 500 degrees C in N2, the films exhibited a low resistivity of 128.7 mu Omega & sdot;cm and clear monoclinic crystallinity. X-ray photoelectron spectroscopy confirmed dominant Mo4+ species and abundant oxygen vacancies, accounting for the high electrical conductivity. When TiO2 was deposited on the annealed MoO2 electrode, the dielectric constant increased to 88.3, indicating rutile phase formation through the template effect. Furthermore, inserting the MoO2 interlayer reduced the equivalent oxide thickness (EOT) and suppressed interfacial layer growth. These results demonstrate that the ALD-deposited MoO2 using a tetravalent precursor serves as an effective conductive electrode and template layer, enabling high-k rutile TiO2 formation and further EOT scaling in advanced DRAM capacitors.