Structural, Optical and Electrical Properties of HfO₂ Thin Films Deposited at Low-Temperature Using Plasma-Enhanced Atomic Layer Deposition

HfO₂ was deposited at 80-250 °C by plasma-enhanced atomic layer deposition (PEALD), and properties were compared with those obtained by using thermal atomic layer deposition (thermal ALD). The ALD window, i.e., the region where the growth per cycle (GPC) is constant, shifted from high temperatures (150-200 °C) to lower temperatures (80-150 °C) in PEALD. HfO₂ deposited at 80 °C by PEALD showed higher density (8.1 g/cm³) than those deposited by thermal ALD (5.3 g/cm³) and a smooth surface (RMS Roughness: 0.2 nm). HfO₂ deposited at a low temperature by PEALD showed decreased contaminants compared to thermal ALD deposited HfO₂. Values of refractive indices and optical band gap of HfO₂ deposited at 80 °C by PEALD (1.9, 5.6 eV) were higher than those obtained by using thermal ALD (1.7, 5.1 eV). Transparency of HfO₂ deposited at 80 °C by PEALD on polyethylene terephthalate (PET) was high (> 84%). PET deposited above 80 °C was unable to withstand heat and showed deformation. HfO₂ deposited at 80 °C by PEALD showed decreased leakage current from 1.4 × 10^-2 to 2.5 × 10^-5 A/cm² and increased capacitance of approximately 21% compared to HfO₂ using thermal ALD. Consequently, HfO₂ deposited at a low temperature by PEALD showed improved properties compared to HfO₂ deposited by thermal ALD.