Oxidant-Free Atomic Layer Deposition of SnO$_2$ Using Complementary Metal Precursors

We report a novel atomic layer deposition (ALD) process for SnO$_2$ that does not require water or other strong oxidizing agents, such as H$_2$O, O$_2$ plasma, O$_3$, or H$_2$O$_2$. 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 SnCl$_4$ acts as an additional tin source. For this precursor combination, an optimal ALD temperature window of 70–90 °C was established, within which amorphous SnO$_2$ 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 SnO$_2$ films and their potential for various applications. To gain mechanistic insight into this oxidant-free SnO$_2$ growth process, we employ density functional theory (DFT) calculations to investigate the surface reactions during sequential exposure of Sn(OtBu)$_4$ and SnCl$_4$ on a SiO$_2$ substrate. ... mehrThe 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 SnO$_2$ ALD mechanism and offers guidance for post-deposition optimization of the material.