Prestressing-Based Thermal Budget Study of MEMS Cantilever and Its Application in Package Processes

Thermal process is an important factor for metal cantilever profile, which may cause stress change and degeneration of device reliability. In this paper, prestressing-based thermal budget study of MEMS cantilever and its application in package processes are conducted. Cantilever profiles are reviewed, modeled and fitted by polynomial functions at different stress gradient situations. The Gold-Nickel (AuNi) alloy cantilevers are fabricated by electroplating process, and the electroplating current density (ECD) is modified from 0.5 to 2.5 ampere per square decimeter (ASD) for residual stress gradient regulation, which is called prestressing method of the cantilever. The profiles of cantilevers are observed by three-dimensional (3D) optical microscope (OM). Responses of cantilevers electroplated by 1.0 ASD are tested pre- and post-thermal processes with dwelling temperatures from 200 to 350 ° C and time from 5 to 30 minutes. On the basis of the evaluation, thermal processes in AuIn and AuSn eutectic bonding are designed and imitated, with temperatures of 200 and 290 ° C, respectively. All of the cantilevers electroplated by ECD from 0.5 to 2.5 ASD are treated by the two designed thermal processes. Among these test results, thermal process with 200 ° C for 5 minutes is suitable for the cantilevers electroplated by 0.75 ASD; and thermal process with 290 ° C for 5 minutes is suitable for the cantilevers electroplated by 1.0 ASD. In conclusion, the prestressing model and thermal budget model are established, which are helpful for realization of the packaged flat cantilever device and its reliability improvement. [2024-0083]