Plasma-Enhanced Atomic Layer Deposition of High-Quality InN Thin Films Using a Liquid Heteroleptic In Precursor and NH3 Plasma

Abstract

Indium nitride (InN) thin films were grown by plasma-enhanced atomic layer deposition (PEALD) using the indium amidinate precursor (N,N′-di-tert-butylacetimidamido)dimethylindium (DBADMIn) and NH3 plasma to realize conductive InN within a BEOL-compatible thermal budget. A self-limiting ALD window between 175 and 275 °C was identified, with a nearly constant growth-per-cycle (GPC) of ≈ 0.56 Å that enabled uniform thickness control. Under the optimized condition of 275 °C, 150 W NH3 plasma, and a 10–10–1–10–10 s sequence, the films exhibited a density of 6.20 g/cm3 with smooth interfaces and crystallized as polycrystalline wurtzite InN with preferred (100), (002), and (101) orientations. Conformality was further supported by step-coverage evaluation on A/R = 2.5 trench features, yielding 91.10% (tside/ttop) and 85.91% (tbottom/ttop) under the optimized condition. Combined Rutherford backscattering spectrometry (RBS) and time-of-flight elastic recoil detection (ToF-ERD) analysis revealed a slightly indium-rich stoichiometry (In:N ≈ 1.47) with measurable oxygen and hydrogen incorporation; oxygen was enriched near the surface but also present within the film interior, reflecting both in-cycle incorporation and post-deposition oxidation. Hall and four-point-probe measurements confirmed degenerate n-type conduction (n ≈ 1 × 1021 cm–3, μ = 5.4 cm2/V·s, ρ ≈ 1000 μΩ·cm), while UV–Vis spectroscopy showed an apparent direct bandgap of ≈ 2.1 eV arising from the Moss–Burstein effect. Time-dependent resistance measurements revealed a gradual increase upon ambient exposure, more pronounced in thinner films, consistent with progressive surface oxidation that modifies near-surface transport and highlights the need for appropriate passivation or capping strategies. These results establish DBADMIn as a thermally stable and surface-reactive precursor for low-temperature, conformal growth of conductive InN thin films and provide a process basis for integrating InN into BEOL-compatible and high-frequency device technologies.