Atomic Layer Deposition of Polycrystalline Tin Dioxide Thin Films Using Liquid Bis（ethylcyclopentadienyl）tin

Abstract

The liquid compound bis（ethylcyclopentadienyl）tin, Sn（EtCp）₂, was synthesized and exhibited several notable characteristics, including a vapor pressure suitable for use as a precursor and thermal stability up to 230 ℃. Using it as a precursor and O₂ plasma as an oxidant, SnO₂ thin films can be deposited by atomic layer deposition（ALD）. A self-limiting reaction was confirmed with no nucleation delay for pulse times of 10 and 45 s for Sn（EtCp）₂ and O₂ plasma, respectively, at a growth temperature of 200 ℃. The growth per cycle（GPC）was 0.20 nm/cycle, which is higher than that of conventional precursors. Cross-sectional transmission electron microscopy revealed that the SnO₂ film was uniform and polycrystalline, even though it was deposited at 200 ℃. X-ray diffraction analysis revealed that the film had a tetragonal rutile SnO₂ structure with a（110）preferred orientation. Sn（EtCp）₂ is a promising precursor for depositing high-quality SnO₂ films with a stoichiometric composition, high purity, and high crystallinity, even at low temperatures.