Al₂O₃ Thin Films Prepared by a Combined Thermal-Plasma Atomic Layer Deposition Process at Low Temperature for Encapsulation Applications

In this article, a combined H₂O thermal atomic layer deposition of Al₂O₃ with in situ N₂ plasma treatment process at 90 °C for encapsulation applications is reported. The effect of process parameters on the growth behavior and properties of Al₂O₃ thin films, such as elemental composition, residual stress, moisture permeation barrier ability, density, and roughness, is investigated. Optimization of plasma exposure time gives films with a low impurity (≈3.8 at% for hydrogen, ≈0.17 at% for carbon, and ≈0.51 at% for nitrogen), a high mass density (≈3.1 g cm⁻³), and a low tensile residual stress (≈160 MPa). A water vapor transmission rate of 2.9 × 10⁻³ g m⁻² day⁻¹ is obtained for polyethylene naphthalate substrates coated with 4-nm-thick Al₂O₃ films.