Vacuum package using anodic bonding assisted by the reflow of low-melting temperature metal

In this paper, we present a highly effective vacuum seal method, which is based on anodic bonding assisted by the reflow of lowmelting temperature metal. To form sacrificial gap for evacuating the packaged cavity before hermetically sealing, the reflow process of Au/Sn/Cr posts due to low-melting temperature Sn metal was introduced. Using this technique to form the evacuation gap, the micro-precise alignment between packaging wafers was obtained. The package method enabled to eliminate contaminant caused by package process. The diaphragm structure sensing pressure was used to investigate the proposed package method. The vacuum level in the packaged cavity was obtained lower than 5 Pa. In comparison to the conventional package method without using the reflow process to form the evacuation gap, the vacuum level has been improved by a factor of 8. The yield and uniformity of the package method were also confirmed to be higher than the conventional package method without using the reflow process to form the evacuation gap. This vacuum package method can be implemented to remove air damping for optimal performance of mechanical oscillators such as accelerometers, gyroscopes, energy harvesters, and micro-mirrors.