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Abstract: Silicon-on-insulator (SOI) wafers made by direct wafer bonding are widely used as starting substrates for microelectromechanical systems (MEMS) fabrication. Adding another layer next to the SiO2 SOI, or replacing it with another material, will be a way to tailor the SOI wafers further. Atomic layer deposition (ALD) can be used to deposit pinhole-free nanometer-thin conformal and smooth inorganic films at low temperatures, making it of interest for many applications in MEMS. In this work, the direct wafer bonding of ALD TiO2, and Al2O3 for reference, is investigated, eventually in order to fabricate SOI wafers with buried ALD oxides. Finding suitable process conditions for TiO2 bonding was challenging: bonding could not be made for TiO2 deposited directly on SiO2 or Si, and annealing at 1100°C gave non-continuous Ti-containing layers. Using a 2-nm Al2O3 under-layer and annealing at 700°C gave void-free bonding with continuous TiO2 and a bond strength of approximately 1600mJ/m2, enabling the fabrication of SOI wafers with buried TiO2. [Copyright &y& Elsevier]

Abstract: Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al2O3 +TiO2 nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20nm and total thickness between 40nm and 60nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements 63Cu, 35Cl, 12C and 4He ions with energies ranging from 0.5 to 10MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5nm individual layer thickness. [Copyright &y& Elsevier]