Eutectic bonding is the connection of two wafers by the formation of an eutectic using one or several metals as an intermediate layer, e.g. gold and silicon. Despite the high melting points of gold and silicon in their pure form, a mixed phase exists that is liquid at 363°C already. This eutectic point allows to initiate a material engagement between both elements at the solid state: Bringing the surfaces into tight contact, the influence of heat and pressure leads to formation of an interdiffusion zone that becomes liquid and thus accelerates the formation of the eutectic phase. Only the precise control of force and temperature in this process as well as additional design measures allow to control the liquid phase and to avoid non-intentional wetting of surrounding structures. Eutectic bonding is insensitive to surface roughness and tolerates even larger topography of the joining surfaces.
ISIT uses this process for the packaging of MEMS resonators and other wafer based components with pre-fabricated cap wafers.