Properties of ALD grown Al2O3-TiO2 laminates investigated by high temperature XRD/XRR and in situ wafer curvature measurements

ALD is based on sequential and self-limiting surface reactions enabling growth of laminated layers of almost any composition and layer thickness. Thin films made by ALD are common in MEMS devices, and depending on the stage where those are applied, they might be exposed to large temperature variations during subsequent processing. Thermomechanical properties of ALD Al2O3-TiO2 (ATO) nanolaminates, grown from TiCl4/TMA and H2O at 200 °C with varying bilayer thickness, were studied here in situ during annealing. In HTXRR data, the superlattice peak indicates quality and interface sharpness of the nanolaminate; the onset of layer mixing is detected from the decrease of peak intensity. The discrete sublayers mixed here already below 450°C. In-situ curvature measurement showed only moderate changes detected upon heating of the structure up to 500°C and back to room temperature. With HTXRD it was found that anatase crystallized first at ~650 °C and rutile at ~725 °C, while corundum appeared at ~900 °C. For most laminates rutile and corundum remained as major phases, only in thickest bilayer there were signs of Al2TiO5/Ti3O5. Combining HTXRD/HTXRR with in-situ curvature measurements help to find processing window for ATO nanolaminates, where depending on application little to no changes in thermomechanical properties are needed. Not only this is useful for MEMS applications where thermal budget influences the usability of the material, but similar methodology can be used to study other laminate structures as well.