Solid-Phase Epitaxy of Perovskite High Dielectric PrAlO3 Films Grown by Atomic Layer Deposition for Use in Two-Dimensional Electronics and Memory Devices

Abstract

An atomic layer deposition (ALD) process is reported for the growth of nanoscale PrAlO3 thin films for two-dimensional electronics and memory device applications using tris(isopropylcyclopentadienyl)praseodymium (Pr(C5H4iPr)3), trimethylaluminum (AlMe3), and water. Pr(C5H4iPr)3 was first evaluated as a precursor for the formation of thin films of the binary oxide Pr2O3 by using water as the coreactant. Self-limited growth of Pr2O3 was demonstrated for pulse lengths of ≥3 s, with a growth rate of ∼0.85 Å/cycle. The ALD growth of PrAlO3 films was examined on Si, thermal SiO2, and (001)-oriented SrTiO3 substrates. Self-limited growth was demonstrated for Pr(C5H4iPr)3, AlMe3, and water at 300 °C by using a 1:1 ratio of the number of Pr(C5H4iPr)3 and AlMe3 pulses. An ALD window was observed from 275 to 325 °C with a growth rate of ∼1.7 Å/cycle. The as-deposited PrAlO3 films on all substrates were amorphous, had smooth surfaces, and contained <0.5% carbon, as analyzed by grazing incidence wide-angle X-ray scattering, X-ray reflectivity, and X-ray photoelectron spectroscopy, respectively. Films grown with a 1:1 ratio of Pr(C5H4iPr)3 and AlMe3 pulses were aluminum-rich (Pr:Al ∼1:1.2-1.4). Heating PrAlO3 layers deposited on SrTiO3 to 800 °C for 3 h resulted in fully crystallized PrAlO3 films. The crystallized PrAlO3 films were highly (001)-oriented. The PrAlO3 00L and SrTiO3 00L reflections appeared on the same rod of reciprocal space, further indicating that the amorphous PrAlO3 film transforms into an epitaxial layer. The rocking curve width of the PrAlO3 (001) reflection was 7°. By contrast, PrAlO3 films deposited on Si substrates with native oxide remained amorphous after annealing at 1000 °C for 8 h. The difference in the crystallization between PrAlO3 layers deposited on crystalline SrTiO3 and amorphous native SiO2 substrates indicates that PrAlO3 on SrTiO3 crystallized by solid-phase epitaxy, in which the nucleation and orientation of the crystallized layer are set by the atomic configuration at the substrate-film interface.