Process Study Of MEMS Wafer Level Packaging

MEMS (Micro Electro Mechanical Systems) is a micro system that integratemicro mechanical element, micro sensor, micro actuator and signal processing&control circuit. MEMS technology has been gradually moving from laboratoryresearch towards the market, the emergence of MEMS products not only develops avery wide range of applications, but also has very strong market competitiveness. Themicro sensor, micro actuator, miniature components and micro mechanical opticaldevices based on MEMS are widely used in aerospace, automobile, medical science,environment monitoring and military fields and so on. Despite the development ofMEMS technology, MEMS packaging is still in the beginning stage and faces manyproblems, due to the diversity and complexity of MEMS device. Packaging format ofMEMS device is the key factor in bringing design scheme of device based on MEMSinto market, and is another important factor in MEMS design and manufacturing. Thebest package can enable the diverse functionalities of MEMS products. In this paper,the microcap packaging technology for radio frequency (RF) device is chosen as theresearch topic. The detailed contents in this article are as follows:(1) Basic theory and the process of wafer-level packaging have been studied andanalyzed in depth, and TSV technology used in MEMS wafer level vacuum packagingis proposed. Several wafer bonding processes, such as direct wafer bonding, anodicbonding, and so on, are compared through selection of material and the processconditions. According to the practical request in application, a practicable scheme ofAu-Au diffusion bonding has been brought forward.(2) The structure and process flow of microcap packaging are completed.Furthermore, the processes of lithography, cavity etching, photoresist removal,bonding, grinding, and electroplating are completed as well.(3) According to the characteristics of the TSV technology, some key processes ofTSV are optimized. The process of TSV is also accomplished through optimizingprocessing techniques and parameters of some principal steps, for instance, deepreactive ion etch (DRIE), coating photoresist on complex substrate with deep hole,and electroplating. The process results are evaluated and analyzed through thescanning electron microscope, step tester and other test equipment.(4) Several improvements have been made to optimize the plasma etching andwet etching of pad. By adjusting dry etching parameters, plasma etching anisotropy can be improved，and smooth plank wall morphology has been obtained. In ourexperiments, adhesiveness between pad and metalmaterial underneath is tested,etching morphology is improved, and technological processes have been simplified.(5) Testing and evaluation of packaging. The bonds were characterized using pulltests. Through the high temperature and high humidity deterioration experiments, thepackaging effects are also verified. Electric properties of encapsulated MEMS deviceare tested using probe station equipment, and the results demonstrate that microcappackaging is reliable.