Atomic layer deposition of dielectric Y₂O₃ thin films from a homoleptic yttrium formamidinate precursor and water

We report the application of tris(N,N'-diisopropyl-formamidinato)yttrium(iii) [Y(DPfAMD)₃] as a promising precursor in a water-assisted thermal atomic layer deposition (ALD) process for the fabrication of high quality Y₂O₃ thin films in a wide temperature range of 150 °C to 325 °C. This precursor exhibits distinct advantages such as improved chemical and thermal stability over the existing Y₂O₃ ALD precursors including the homoleptic and closely related yttrium tris-amidinate [Y(DPAMD)₃] and tris-guanidinate [Y(DPDMG)₃], leading to excellent thin film characteristics. Smooth, homogeneous, and polycrystalline (fcc) Y₂O₃ thin films were deposited at 300 °C with a growth rate of 1.36 Å per cycle. At this temperature, contamination levels of C and N were under the detectable limits of nuclear reaction analysis (NRA), while X-ray photoelectron spectroscopy (XPS) measurements confirmed the high purity and stoichiometry of the thin films. From the electrical characterization of metal-insulator-semiconductor (MIS) devices, a permittivity of 13.9 at 1 MHz could be obtained, while the electric breakdown field is in the range of 4.2 and 6.1 MV cm^-1. Furthermore, an interface trap density of 1.25 × 10¹¹ cm^-2 and low leakage current density around 10^-7 A cm^-2 at 2 MV cm^-1 are determined, which satisfies the requirements of gate oxides for complementary metal-oxide-semiconductor (CMOS) based applications.