Oxidant-Free Atomic Layer Deposition of SnO2 Using Complementary Metal Precursors

We report a novel atomic layer deposition (ALD) process for SnO2 that does not require water or other strong oxidizing agents, such as H2O, O2 plasma, O3, or H2O2. The development of alternative oxidant-free ALD processes is highly attractive because it enables a gentler and more controllable chemical environment, which is crucial for next-generation nanoscale devices and complex material stacks. In this approach, Sn-based complementary metal precursors are employed: Sn(OtBu)4 serves as both the tin and oxygen precursor, while SnCl4 acts as an additional tin source. For this precursor combination, an optimal ALD temperature window of 70-90 °C was established, within which amorphous SnO2 films are deposited. Post-deposition annealing is subsequently required to develop the desired crystallinity and to adjust the oxygen-vacancy concentration and impurity levels, which ultimately determine the electrical and optical properties of the resulting SnO2 films and their potential for various applications. To gain mechanistic insight into this oxidant-free SnO2 growth process, we employ density functional theory (DFT) calculations to investigate the surface reactions during sequential exposure of Sn(OtBu)4 and SnCl4 on a SiO2 substrate. The results reveal key atomic-level processes, including ligand-exchange pathways, oxygen transfer, and surface regeneration, which govern film growth. This combined experimental and theoretical approach provides fundamental understanding of the SnO2 ALD mechanism and offers guidance for post-deposition optimization of the material.