Silicon wafer bonding techniques for assembly of micromechanical elements

Different bonding techniques under development for assembly of micromechanical elements are reviewed. A versatile wafer-to-wafer bonding process using silicon-to-silicon anodic bonding with sputtered Pyrex 7740 borosilicate thin film has been developed. The method gives sealings with a bonding strength of approximately 2.5×10⁶ N/m² and excellent thermal matching, resulting in minimized thermally induced stress in micromechanical components. The anodic bonding is performed at temperatures well below the aluminum/silicon eutectic temperature, making the process suitable also for metallized wafers. The large electrostatic force obtained during bonding is crucial for a high-yield wafer-to-wafer bonding process. High bonding strength and complete bonding of 3-in wafers were obtained. This technique was used for a silicon pressure sensor application, giving excellent thermal and long term stability for this sensor. The results are supported by finite-element calculations