Substrate temperature effects on PEALD HfAlO dielectric films for IGZO-TFT applications

Aluminum incorporated hafnium oxide (HfAlO) has garnered significant attention due to its high dielectric constant. The present study employs supercycle plasma-enhanced atomic layer deposition (PEALD) to prepare HfAlO films, switching between HfO2 and Al2O3 deposition. The effects of substate temperature on the HfAlO films are systematically investigated. The experimental results indicate that increased substrate temperatures favor Al2O3 growth on HfO2, but excessively high temperatures result in deviated PEALD growth and deteriorated film properties. The PEALD window can be reached at substrate temperatures of 300 to 350 °C. The Al content is substantially affected by the substrate temperature, despite a constant Al2O3 PEALD cycle ratio used. The film deposited at 350 °C exhibits the highest Al content, density, and (1 1 1) crystalline orientation ratio, leading to a high breakdown field of 6 MV/cm and a considerable dielectric constant of 27. The HfAlO films are applied to indium gallium zinc oxide transistor as the dielectric layer, and the 350 °C-deposited HfAlO leads to the best device performance with a remarkably high on/off current ratio of 3.5 × 109, low threshold voltage of −0.1 V, saturated mobility of 6.1 cm2 V−1 s−1, and a low subthreshold swing of 76 mV/dec.