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    Aluminum Nitride to Silicon Direct Bonding for an Alternative Silicon-On-Insulator Platform

    Year: 2021

    Journal: ACS Appl. Mater. Interfaces, Volume 13, AUG 18, page 38857–38865

    Authors: Kaaos, Jani; Ross, Glenn; Paulasto-Krockel, Mervi

    Organizations: Innovation Funding Agency Business Finland [826653]

    Keywords: silicon-on-insulator; direct bonding aluminum nitride; microelectromechanical systems; plasma activation; surface chemistry; surface topography

    The next generation of microelectromechanical systems (MEMS) requires new materials and platforms that can exploit the intrinsic properties of advanced materials and structures, such as materials with high thermal conductivity, broad optical transmission spectra, piezoelectric properties, and miniaturization potential. Therefore, we need to look beyond standard SiO2-based silicon-on-insulator (SOI) structures to realize ubiquitous MEMS. This work proposes using AIN as an alternative SOI structure due to several inherent material property advantages as well as functional advantages. This work presents the results of reactively sputtered AIN films on a Si handle wafer bonded with a mirror-polished Si device wafer. Wafer bonding was achieved by using hydrophilic wafer bonding processes, which was realized by appropriate polymerization of the prebonding surfaces. Plasma activation of the AIN surface included O-2 Ar, SF6, SF6 + Ar, and/or SF6 + O-2, which resulted in a change in the chemical and topography state of the surface. Changes in the AIN surface properties included enhanced hydrophilicity, reduced surface roughness, and low nanotopography, components essential for successful hydrophilic direct wafer bonding. Wafer bonding experiments were carried out using promising surface activation methods. The results showed a multilayered bonding interface of Si(Device)/SiO2/ALON/AIN/Si(Handle) with fluorine in the aluminum oxynitride layer from the proceeding AIN surface activation process. More notably, this work provided wafer bonding tensile strength results of the AIN alternative SOI structure that compares with the traditional SiO2 SOI counterpart, making AIN to Si direct bonding an attractive alternative SOI platform.
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