Atomic layer deposition (ALD) offers a viable route for the growth of thin and conformal films over 3D topographies and is becoming attractive as a method to grow films thin enough, and with sufficient dielectric constants (k), for the fabrication of next-generation dynamic random memories. The authors used ALD to grow thin (≤15 nm) BaxSr1 − xTiO3 (BST) films that are epitaxially integrated to SrTiO3 (001) (STO) and Nb-doped SrTiO3 (001) (Nb:STO). Films of three compositions, which are x ∼ 0.7, 0.5, and 0.3, and thicknesses of 7.8–14.9 nm were grown at 1.05 Torr and 225 °C using barium bis(triisopropylcyclopentadienyl), strontium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide, and H2O. Film compositions were controlled by changing cycle ratios (Ba:Sr, Ba:Ti, and Sr:Ti) and confirmed by in situ x-ray photoelectron spectroscopy. Films were amorphous as-deposited and required postdeposition vacuum annealing at 650–710 °C to crystallize. Epitaxy was confirmed with x-ray diffraction and transmission electron microscopy. Only BST (00l) out-of-plane diffraction signals were detected. Capacitance-voltage (C-V) measurements revealed that BST thin films grown by ALD have dielectric constant values ranging from 210 for Ba0.71Sr0.26TiO3 to 368 for Ba0.48Sr0.43TiO3.

This work reports the atomic layer deposition (ALD) and epitaxial growth of 10–12 nm BaxSr1−xTiO3 (x ∼ 0.5) thin films on Zintl-templated Ge (001) substrates, formed with 0.5 monolayers of Ba. The best thin films were grown using two steps. An amorphous 2–3 nm layer was deposited at 225 °C and then was converted to a crystalline film by annealing for 15 min at 650 °C under vacuum to generate the seed layer that had an abrupt interface with the Ge (001) substrate. A 7–10 nm layer was subsequently grown and crystallized at the same conditions as the seed layer. Metal-insulator-semiconductor structures that employed Au electrodes were used to assess leakage currents and dielectric properties. Interfacial effects inherent to the ∼10 nm BaxSr1−xTiO3 films affect the capacitance measurements leading to k of 87 and 140 for 10.9 and 14.6 nm films, respectively. The epitaxial films have high k in the bulk. Using capacitance measurements for BaxSr1-xTiO3 films that are 13–18.4 nm thick, a bulk k of ∼2000 and low interfacial capacitance density (C/A) of ∼100 fF/μm2 were extracted from thickness dependent relationships. The 10 nm films display a high leakage current (∼102 A/cm2 at −1.0 V) that can be reduced (to ∼10−1 A/cm2 at −1.0 V) by capping the film with ∼1 nm Al2O3 using ALD before depositing the Au electrode or by annealing in O2 at 300 °C for 15 min. The thin low-k Al2O3 layer or the GeOx formed during the O2 annealing step, while improving leakage current, introduces a capacitor in series that further reduces the film dielectric constant such that a 9.9 nm Al-capped film and a 9.8 nm O2-annealed film yield dielectric constants of 80 and 41, respectively.

Atomic layer deposition (ALD) offers a viable route for the growth of thin and conformal films over 3-D topographies and is becoming attractive as a method to grow films thin enough, and with sufficient dielectric constants (k), for the fabrication of next-generation dynamic random memories (DRAMs). Through isovalent A-site substitution of Sr for Ba in the ABO3 perovskite the dielectric constant can be tuned to be orders of magnitude greater than either SrTiO3 or BaTiO3 near ambient temperatures. We used ALD to grow thin (≤ 15 nm) Ba x Sr1-x TiO3 (BST) films that are epitaxially integrated to SrTiO3 (001) (STO) and Zintl-templated Ge (001). Films of three compositions, which are x ~ 0.7, 0.5 and 0.3, and thicknesses of 7.8 to 14.9 nm were grown at 1.05 Torr and 225 °C using barium bis(triisopropylcyclopentadienyl), strontium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide and H2O. Film compositions were controlled by changing cycle ratios (Ba:Sr, Ba:Ti and Sr:Ti) and confirmed by in situ X-ray photoelectron spectroscopy (XPS). Films were amorphous as deposited and required post-deposition vacuum annealing at 650-710 °C to crystallize. Epitaxy was confirmed with X-ray diffraction and transmission electron microscopy. Only BST (00l) out-of-plane diffraction signals were detected. Capacitance-voltage (C-V) measurements revealed that BST thin films grown by ALD on STO (001) have dielectric constant values ranging from 210 for Ba0.71Sr0.26TiO3 to 368 for Ba0.48Sr0.43TiO3. The dielectric constant k increased with thickness with x in the range of 0.27 ≤ x ≤ 0.31. Interfacial effects inherent to the ~ 10 nm Ba x Sr1-x TiO3 films on Ge (001) affect the capacitance measurements leading to k of 87 and 140 for 10.9 and 14.6 nm films, respectively. The epitaxial films have high k in the bulk. Using capacitance measurements for Ba x Sr1-x TiO3 films (x~0.5) 13 to 18.4 nm thick, a bulk k of 3200 at RT and a low interfacial capacitance density (C/A) of 100 fF/mm2 were extracted from thickness dependent relationships.