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Wafer bonding is a crucial process for fabricating microsystems. Within this study, the polymer parylene was used to establish a low-temperature adhesive wafer bonding process for wafers of 150 and 200 mm diameters. The bonding process was investigated for silicon and glass wafers with different additional coatings including silicon dioxide, silicon nitride, aluminum, and parylene C. Important process parameters such as bonding temperature and time were also investigated and the parylene adhesive was analyzed in detail with respect to its dimensions and type. The performance of the parylene bonding was characterized in different aspects, including mechanical tests, cross-sectional scanning electron microscopy, infrared light transmission, and different hermeticity tests. The reliability of the parylene bonded compounds was also investigated with respect to constant loading, mechanical shocking, and thermal cycling. As a result, the parylene bonding is feasible with various materials and shows high tensile and shear strengths of up to 35 MPa and 80 MPa, respectively. Hermeticity was excellent, with a helium leakage rate lower than 10‒7 mbar∙l s−1. The parylene bonded compounds were proven to feature high reliability. Finally, application of the superior properties of the parylene bonding was demonstrated with respect to the fabrication of different three-dimensional structures.

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The ongoing miniaturization and implementation of new functionalities into micro-electro-mechanical systems (MEMS) demand the development and application of new wafer bonding and encapsulation technologies with a high performance. Requirements are low process temperatures, high mechanical strengths of the bonded interface, as well as the applicability on large wafer sizes. Within the presented study, the polymer Parylene C was used as an adhesive for the bonding of 6” and 8” wafers. Doing so, the material combinations of the wafers, the Parylene thicknesses and geometries as well as the bonding parameters were varied. The properties of the wafer compounds were characterized with various methods, including mechanical tests, infrared imaging, cross-sections, hermeticity tests and the investigation of the thermal reliability. Using the Parylene C bonding process, tensile strengths of up to 35 MPa, and shear strengths of up to 80 MPa were realized. The determined helium leakage rate was lower than 1 ∙ 10-7 mbar ∙ l/s and the thermal reliability was verified to be excellent.