Epitaxial growth of high-k BaxSr1-xTiO3 thin films on SrTiO3 (001) substrates by atomic layer deposition

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 (<= 15nm) 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 similar to 0.7, 0.5, and 0.3, and thicknesses of 7.8-14.9nm were grown at 1.05Torr and 225 degrees 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 degrees 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.