In-situ temperature monitoring for process control in laser assisted polymer bonding for MEMS packaging

Laser assisted polymer bonding is a novel promising technique for MEMS packaging. In this method, a thermally cured polymer seal using localised laser heating is used to produce a microcavity between a capping substrate and a MEMS chip or wafer. The cavity is necessary to protect the fragile micromechanical structures of the MEMS devices in the subsequent manufacturing processes after wafer fabrication and to provide a stable environment for operation. The laser based bonding method is a fast process and can reduce/eliminate the potential damage to temperature sensitive devices during packaging. However, due to the localised nature of the temperature rise it is difficult to monitor the temperature change precisely during the bonding process using conventional methods. In this paper we present the development of thin film miniature temperature sensors for in-situ processing monitoring in the laser assisted polymer bonding process for MEMS packaging. Distributed temperature sensors are fabricated on the substrate and are successfully used to monitor the in-situ temperature rise and distribution in the bonding process.