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

Abstract

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 (MoO 2 ) 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 MoO 2 exhibits a distorted rutile structure, enabling the in situ growth of high-k rutile TiO 2 on MoO 2 at low deposition temperatures. However, MoO 2 deposition poses challenges because of its metastable nature compared to the more stable molybdenum oxide (MoO x ) phases, such as MoO 3 and Mo 4 O 11 . In this work, we successfully fabricated Sn-doped MoO x (TMO) films by atomic layer deposition (ALD) at 300 °C. A stabilized monoclinic MoO 2 phase was achieved using ALD by incorporating SnO x into MoO x on both SiO 2 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 TiO 2 , possessing a negligible low-k interfacial layer. Moreover, a rutile TiO 2 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 MoO 2 films using ALD, and it demonstrates the superiority of ALD TMO as a promising DRAM capacitor electrode material.