Atomic layer deposition of Y2O3 films using a novel liquid homoleptic yttrium precursor tris(sec-butylcyclopentadienyl)yttrium [Y(sBuCp)3] and water

Abstract

Atomic layer deposition (ALD) of Y₂O₃ thin films was studied using a novel homoleptic yttrium ALD precursor: tris(sec-butylcyclopentadienyl)yttrium [Y(^sBuCp)₃]. Y(^sBuCp)₃ is a liquid at room temperature. The thermogravimetry curve for Y(^sBuCp)₃ is clean, with no indication of decomposition or residue formation. Thermogravimetry–differential thermal analysis measurements showed that Y(^sBuCp)₃ is stable for 18 weeks at 190 °C. Y(^sBuCp)₃ has a homoleptic structure. Thus, a reduction in manufacturing costs is expected compared to those associated with heteroleptic precursors because additional chemical synthesis steps are usually necessary to produce heteroleptic compounds. In addition, ALD of Y₂O₃ was demonstrated using Y(^sBuCp)₃ and water as a co-reactant. The deposition temperature was varied from 200 to 350 °C. The growth rate was 1.7 Å per cycle. In addition, neither carbon nor nitrogen contamination was detected in the Y₂O₃ films by X-ray photoelectron spectroscopy. Furthermore, smooth films were confirmed by X-ray secondary-electron microscopy. The root-mean-square roughness was measured to be 0.660 nm by atomic force microscopy. Metal–insulator–semiconductor (MIS) Pt/Y₂O₃/p-Si devices were fabricated to evaluate the electrical properties of the Y₂O₃ films. An electric breakdown field of −6.5 MV cm⁻¹ and a leakage current density of ∼3.2 × 10⁻³ A cm⁻² at 1 MV cm⁻¹ were determined. The permittivity of Y₂O₃ was estimated to be 11.5 at 100 kHz. Therefore, compared with conventional solid precursors, Y(^sBuCp)₃ is suitable for use in ALD manufacturing processes.