High-Temperature Atomic Layer Deposition of Rutile TiO₂ Films on RuO₂ Substrates: Interfacial Reactions and Dielectric Performance

Capacitor structures utilized in modern dynamic random access memory (DRAM) cells require the conformal growth of high-k films on electrode materials. In this context, the atomic layer deposition (ALD) of rutile-phase TiO₂ on nearly lattice-matched substrates such as RuO₂ has been extensively explored. It is typically desired to grow such insulating films at high temperatures to ensure low defect concentrations and high crystallinity. However, with increasing growth temperature, it is also crucial to consider the aggravated effect of interface reactions that could potentially hinder final device performance. Here, we report the high-temperature ALD growth of TiO₂ on RuO₂ substrates using the heteroleptic precursor trimethoxy(pentamethylcyclopentadienyl)titanium ((CpMe₅)Ti(OMe)₃) and O₃. High-quality, rutile-phase TiO₂ films with large dielectric constants of ∼100 could be grown at temperatures exceeding 300 °C. When the growth temperature reaches 330 °C, we find that an anomalous RuO₂ reduction reaction occurs due to interactions between the substrate and Ti precursor. The reduced Ru is transformed into volatile RuO₄ during the subsequent O₃ injection steps, resulting in partial etching of the substrate. Simple RuO₂/TiO₂/RuO₂ capacitor devices fabricated from optimized films demonstrate excellent dielectric performance with an equivalent oxide thickness (EOT) of 0.5 nm at leakage current densities of less than 10^-7 A/cm². A further reduction of EOT to 0.4 nm could be achieved by implementing a single cycle of Al doping to the TiO₂ films, surpassing the benchmark values proposed for next-generation DRAM capacitors by a safe margin. Our findings clearly showcase the benefits of high-temperature ALD in the semiconductor technology, as well as providing guidelines for the interpretation of the convoluted interface reactions tied to its implementation.