Atomic layer deposition of Gd ₂O ₃ and Dy ₂O ₃: A study of the ALD characteristics and structural and electrical properties

Gd ₂O ₃ and Dy ₂O ₃ thin films were grown by atomic layer deposition (ALD) on Si(100) substrates using the homoleptic rare earth guanidinate based precursors, namely, tris(N,N′- diisopropyl-2-dimethylamido-guanidinato)gadolinium(III) [Gd(DPDMG) ₃] (1) and tris(N,N′-diisopropyl-2-dimethylamido-guanidinato)dysprosium(III) [Dy(DPDMG) ₃] (2), respectively. Both complexes are volatile and exhibit high reactivity and good thermal stability, which are ideal characteristics of a good ALD precursor. Thin Gd ₂O ₃ and Dy ₂O ₃ layers were grown by ALD, where the precursors were used in combination with water as a reactant at reduced pressure at the substrate temperature ranging from 150 °C to 350 °C. A constant growth per cycle (GPC) of 1.1 Å was obtained at deposition temperatures between 175 and 275 °C for Gd ₂O ₃, and in the case of Dy ₂O _3, a GPC of 1.0 Å was obtained at 200-275 °C. The self-limiting ALD growth characteristics and the saturation behavior of the precursors were confirmed at substrate temperatures of 225 and 250 °C within the ALD window for both Gd ₂O ₃ and Dy ₂O ₃. Thin films were structurally characterized by grazing incidence X-ray diffraction (GI-XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM) analyses for crystallinity and morphology. The chemical composition of the layer was examined by Rutherford backscattering (RBS) analysis and Auger electron spectroscopy (AES) depth profile measurements. The electrical properties of the ALD grown layers were analyzed by capacitance-voltage (C-V) and current-voltage (I-V) measurements. Upon subjection to a forming gas treatment, the ALD grown layers show promising dielectric behavior, with no hysteresis and reduced interface trap densities, thus revealing the potential of these layers as high-k oxide for application in complementary metal oxide semiconductor based devices.