Ultrahigh purity plasma-enhanced atomic layer deposition and electrical properties of epitaxial scandium nitride

Scandium nitride (ScN) by plasma-enhanced atomic layer deposition (PEALD) was demonstrated on silicon (100), sapphire (0001), and magnesium oxide (001) substrates under ultrahigh purity conditions using a new Sc precursor, bis(ethylcyclopentadienyl)scandium-chloride [ClSc(EtCp)(2)]. Out-of-plane x-ray diffraction patterns indicated single-crystal, cubic phase ScN deposited at 215 degrees C on sapphire (0001) and magnesium oxide (001) substrates, whereas phi-scans confirmed epitaxial growth. The ScN thin films grown on silicon with native oxide were polycrystalline with no preferential orientation. The ScN films showed a nitrogen-to-scandium ratio of approximately 1:1 measured by x-ray photoelectron spectroscopy, with ultra-low levels of elemental impurities including 2.5 at. % chlorine, 0.9 at. % carbon, and 0.4 at. % oxygen. ClSc(EtCp)(2) and N-2-H-2 plasma were evaluated as ScN co-precursors at substrate temperatures ranging from 200 to 300 degrees C, where we identified an atomic layer deposition window between 200 and 215 degrees C. Images by field emission scanning electron microscopy (FESEM) on 43 nm-thick films grown on untreated silicon revealed columnar grains with lateral sizes ranging from 16 to 28 nm. ScN conformality across 4:1 aspect ratio silicon trench structures with 312 nm-wide openings was also imaged by FESEM showing a top-to-bottom thickness ratio of 75%. ScN electrical properties were evaluated by performing Hall measurements to determine mobility, free electron concentration, and resistivity. For ScN PEALD on magnesium oxide (001), the average mobility was 298 cm(2)/V s with a carrier concentration of 2.35 x 10(19) cm(-3). The average resistivity was 1.01 m Omega cm.