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 °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 N2–H2 plasma were evaluated as ScN co-precursors at substrate temperatures ranging from 200 to 300 °C, where we identified an atomic layer deposition window between 200 and 215 °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 cm2/V s with a carrier concentration of 2.35 × 1019 cm−3. The average resistivity was 1.01 mΩ cm.