Silicon full wafer bonding with atomic layer deposited titanium dioxide and aluminum oxide intermediate films

Silicon full wafer bonding with atomic layer deposited titanium dioxide and aluminum oxide intermediate films

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 1600 mJ/m², enabling the fabrication of SOI wafers with buried TiO₂.

Keywords

• • Atomic layer deposition;
  • ALD;
  • Wafer bonding;
  • Silicon-on-insulator;
  • SOI;
  • Al₂O₃;
  • TiO₂

Source:Sciencedirect

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