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
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Source:Sciencedirect

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