MOEMS for Space Applications: The Challenge of Multi-Wafer Bonding

MOEMS devices are key devices for next generation optical instruments, including space missions for Earth and Universe Observation. They will be used for object/wavelength selection and wavefront control. MIRA is a European development of micro-mirror arrays, with 100 × 200µm
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silicon mirrors with remarkable surface quality and actual ability to work at cryogenic temperatures (162K). The challenge of multi-wafer bonding, especially on silicon micro-pillars is developed in this paper. Three bonding methods are proposed as well as various non-destructive and destructive methods of bonding characterisation. Low-temperature plasma-assisted Si-SiO
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direct bonding is described in details as very promising method to obtain strong bond on micropillars.