Self-limiting atomic layer deposition of barium oxide and barium titanate thin films using a novel pyrrole based precursor

Abstract

Barium oxide (BaO) is a critical component for a number of materials offering high dielectric constants, high proton conductivity as well as potential applicability in superconductivity. For these properties to keep pace with continuous device miniaturization, it is necessary to study thin film deposition of BaO. Atomic layer deposition (ALD) enables single atomic layer thickness control, conformality on complex shaped substrates, and the ability to precisely tune stoichiometry. Depositing multicomponent BaO containing ALD films in a self-limiting manner at low temperatures may extend the favorable bulk properties of these materials into the ultrathin film regime. Here we report the first temperature and dose independent thermal BaO deposition using a novel pyrrole based Ba precursor (py-Ba) and water (H₂O) as the co-reactant. The growth per cycle (GPC) is constant at 0.45 Å with excellent self-terminating behavior. The films are smooth (root mean squared (RMS) roughness 2.1 Å) and contain minimal impurities at the lowest reported deposition temperatures for Ba containing films (180–210 °C). We further show conformal coating of non-planar substrates (aspect ratio ∼ 1 : 2.5) at step coverages above 90%. Intermixing TiO₂ ALD layers, we deposited amorphous barium titanate with a dielectric constant of 35. The presented approach for infusing self-terminating BaO in multicomponent oxide films may facilitate tuning electrical and ionic properties in next-generation ultrathin devices.