Growth of Atomic layer-deposited Monoclinic Molybdenum Dioxide Films Stabilized by Tin Oxide Doping for DRAM...

Dynamic random-access memory (DRAM) capacitor electrodes, exemplified by TiN, face performance limitations owing to their relatively low work functions in addition to the formation of a low-k interfacial layer caused by their insufficient chemical stability. With recent advances in device scaling, these issues have become increasingly problematic, prompting the exploration of alternative electrode materials to replace TiN. Molybdenum dioxide (MoO₂) has emerged as a promising candidate for this application, outperforming TiN due to its low resistivity, high work function (>5 eV), and excellent chemical stability. Moreover, monoclinic MoO₂ exhibits a distorted rutile structure, enabling the in situ growth of high-k rutile TiO₂ on MoO₂ at low deposition temperatures. However, MoO₂ deposition poses challenges because of its metastable nature compared to the more stable molybdenum oxide (MoO_x) phases, such as MoO₃ and Mo₄O₁₁. In this work, we successfully fabricated Sn-doped MoO_x (TMO) films by atomic layer deposition (ALD) at 300 °C. A stabilized monoclinic MoO₂ phase was achieved using ALD by incorporating SnO_x into MoO_x on both SiO₂ and TiN substrates. The ALD TMO process comprised MoO_x and SnO_x subcycles, and the MoO_x:SnO_x subcycle ratio was varied from 100:1 to 20:1. High growth rates ranging from 0.19 to 0.34 nm/cycle were achieved for ALD TMO with varying the MoO_x:SnO_x subcycle ratio from 20:1 to 100:0. After post-deposition annealing at 500 °C, polycrystalline TMO films were obtained with smooth surface morphology. ALD TMO exhibited excellent interface quality with ALD TiO₂, possessing a negligible low-k interfacial layer. Moreover, a rutile TiO₂ film with a high dielectric constant of 136 was successfully grown on a 20% Sn-TMO electrode. Overall, this study provides a strategy to stabilize metastable MoO₂ films using ALD, and it demonstrates the superiority of ALD TMO as a promising DRAM capacitor electrode material.