Aluminum oxide/titanium dioxide nanolaminates grown by atomic layer deposition: Growth and mechanical properties

Atomic layer deposition (ALD) is based on self-limiting surface reactions. This and cyclic process enable the growth of conformal thin films with precise thickness control and sharp interfaces. A multilayered thin film, which is nanolaminate, can be grown using ALD with tuneable electrical and optical properties to be exploited, for example, in the microelectromechanical systems. In this work, the tunability of the residual stress, adhesion, and mechanical properties of the ALD nanolaminates composed of aluminum oxide (Al₂O₃) and titanium dioxide (TiO₂) films on silicon were explored as a function of growth temperature (110-300 C), film thickness (20-300 nm), bilayer thickness (0.1-100 nm), and TiO₂ content (0%-100%). Al₂O₃ was grown from Me₃Al and H₂O, and TiO₂ from TiCl₄ and H₂O. According to wafer curvature measurements, Al₂O₃/TiO₂ nanolaminates were under tensile stress; bilayer thickness and growth temperature were the major parameters affecting the stress; the residual stress decreased with increasing bilayer thickness and ALD temperature. Hardness increased with increasing ALD temperature and decreased with increasing TiO₂ fraction. Contact modulus remained approximately stable. The adhesion of the nanolaminate film was good on silicon.