Stress in atomic layer deposited aluminium oxide and titanium dioxide thin films

Understanding the stress behaviour in atomic layer deposited (ALD) thin films enables the optimization of the surface microelectromechanical systems (MEMS) device design. To achieve stress control, we need to characterize how different factors influence the stress in ALD thin films. Stress in ALD aluminium oxide (Al2O3) and titanium dioxide (TiO2) thin films were studied on 150 mm silicon (100) wafers as a function of deposition temperature and layer thickness. Deposition temperature was varied from 110 to 300 °C and layer thickness was varied from 10 to 600 nm. Deposition reactor was Picosun SUNALETM R-150 with water (H2O) based processes. Precursors in use were trimethylaluminum (Me3Al) for Al2O3 and titanium tetrachloride (TiCl4) for TiO2. Stresses in ALD thin films were determined using surface profilometer Veeco Dektak and wafer curvature method. Stresses were calculated using Stoney s equation. Composition was determined with time-of-flight elastic recoil detection analysis (TOF-ERDA) and thickness and density with X-ray reflectivity (XRR). All ALD thin films were measured to be under tensile stress. The stress levels of Al2O3 decreased with increasing deposition temperature. When the influence of the layer thickness was studied with Al2O3 in constant temperature, 300°C, the stress levels increased slightly with decreasing film thickness. Stress adjustment by temperature and thickness seems to be more complicated with TiO2, where the crystallization influences the stress level.