Low Temperature Wafer Bonding: Plasma Assisted Silicon Direct Bonding vs. Silicon-Gold Eutectic Bonding

摘要

This paper describes the development of two bonding techniques for structured silicon wafer pairs. The focus was set to low-temperature bonding to make the process compatible to a broad range of applications. First, we present a low temperature plasma-assisted hydrophilic bonding process that can be applied using standard clean room equipment. Unfortunately, direct bonding requires a smooth, undisturbed bonding surface with a roughness in the angstrom regime as a crucial prerequisite. Some complex MEMS process flows are unable to comply with that. Therefore, the second focus was set onto an eutectic silicon-gold wafer bonding process, that has a good tolerance against surface topographies due to the formation of a liquid phase at the bond interface. For surface characterization, contact angle and AFM measurements were carried out, the mechanical characterization of the bond was done by a blister and a tensile test method. Finally, a bonded micro fluidic device is presented.