Direct Etched Silicon Wafer Bonding for Micro-Electromechanical Systems (MEMS).

Micro electro-mechanical system (MEMS) is a chip-based technology where sensors are composed of a suspended mass between a pair of capacitive plates. When the sensor is tilted due to any motion, i.e., acceleration, the suspended mass generates a difference in electrical potential, which is then measured as a change in capacitance. MEMS sensors are capable of meeting performance requirements in a low size, weight, and power (SWaP) package. The wafer bonding is a key step for the fabrication of such a MEMS device. However, the conventional direct wafer bonding technique requires extremely clean and smooth surfaces to be bonded, thus excluding silicon wafers with fabricated patterns as candidates for direct wafer bonding. The proposed silicon-to-silicon wafer bonding technology can form a complete bond between silicon wafers where patterns have been fabricated. The bonding process consists of three steps: surface treatment, prebonding, and bonding. The surface treatment is to remove any contaminations on the surface and create favored chemical groups on the surface. The prebonding process is to form the initial bridge between chemical groups while the bonding process is to form a permanent bond between two surfaces. The bonded stack has been demonstrated in Phase I to be hermetically sealed by bonding itself, thus no getter or gas evacuation is required to be involved after bonding. The bonding strength is in the order of 10 MPa, and it has been demonstrated in Phase I that the bonded stack can survive harsh thermal and mechanical environments, such as temperatures ranging from -55 °C to 85 °C, vibration, shock, and constant acceleration.