Low-Temperature Layer-by-Layer Epitaxy of Ferroelectric Al 0.63 Sc 0.37 N Thin Films for Back-End-of-Line Integration

Sc-doped aluminum nitride ((Al,Sc)N) is a promising material for next-generation nonvolatile memory and MEMS applications for its robust ferroelectricity and CMOS compatibility. However, the large coercive field remains the roadblock. Acquiring high Sc content-doped (Al,Sc)N epitaxial thin films is essential to reduce the coercive field but remains challenging, especially at low temperature for back-end-of-line (BEOL) integration. Here we demonstrate the layer-by-layer epitaxial growth of ferroelectric Al_0.63Sc_0.37N thin films (highest Sc content in epitaxial films) at 400 °C by developing a nitrogen-plasma-assisted pulsed laser deposition (N-PLD) technique. Verified by X-ray photoelectron spectroscopy analysis, the atomic nitrogen atmosphere is crucial to suppress nitrogen vacancies and stabilize the high Sc content (Al,Sc)N wurtzite phase. The high-quality epitaxial Al_0.63Sc_0.37N thin films show high remanent polarization >160 μC cm^-2 and desirable low coercive field of ∼2.9 MV cm^-1. Our results open a new pathway for high-quality (Al,Sc)N BEOL integration for nonvolatile memory and MEMS applications.