Influence of In Situ Atomic Layer Annealing and Plasma-Enhanced Atomic Layer Deposition Techniques for Low-Temperature Deposition of HfO2 High-κ Gate Dielectrics
Abstract
Achieving high electrical quality gate dielectrics for thin-film transistors atop flexible substrates is a challenge due to thermal constraints imposed by the soft and sensitive substrates. This study examines a multitude of deposition pathways using rigid metal–insulator–metal (MIM) capacitors to discern effective solutions. This study provides a comprehensive evaluation of both material characterization and electrical performance of HfO2-based MIM capacitors fabricated using three ALD processes: (1) standard as-deposited thermal atomic layer deposition (TALD), (2) plasma-enhanced ALD (PEALD) at 200 and 250 W (PEALD200, PEALD250), and (3) in situ atomic layer annealing (ALA)-ALD at similar plasma power (ALA200 and ALA250). Material characterization highlights the impact of deposition conditions on film quality. X-ray reflectivity (XRR) revealed improved film density and reduced surface roughness for PEALD250 and ALA processes compared to TALD, while X-ray photoelectron spectroscopy (XPS) verified stoichiometric HfO2 with minimal hydroxyl incorporation under optimized plasma and ALA conditions. Electrical characterization demonstrated clear process-dependent differences in capacitance, dielectric constant, interfacial trap density (Dit), and leakage current. Capacitance–voltage measurements exhibited slight bias dependence and frequency dispersion, indicative of interfacial polarization and dipolar relaxation. TALD films delivered the highest capacitance (∼1.3 μF/cm–2) due to reduced thickness using the same precursor pulse steps but suffered from a lower dielectric constant (εr ≈ 23) and elevated leakage (∼2 × 10–7 A cm–2). In contrast, ALA processed devices achieved the best overall performance, combining a high dielectric constant (εr ≈ 26), ultralow leakage (∼1 × 10–7 and 9 × 10–8 A cm–2), and reduced trap density (6.4 × 1012 and 1.4 × 1013 cm–2eV−1), attributed to enhanced film densification and suppressed oxygen vacancies. These results position ALA-based processes as promising candidates for high-κ dielectrics in advanced MIM capacitors and gate dielectric applications, offering improved reliability and scalability for next-generation electronics.