Micro Electro-Mechanical Systems (MEMS)

Typical process technologies for MEMS device manufacturing include wet etching, dry etching, sacrificial layer technology, bonding, and SOI with cavity. Wet and dry etching processes are also common in standard CMOS processes, but they are uniquely different in MEMS technology. The wet etching in MEMS process is mainly different in the etching depth, anisotropic wet etching skillfully for achieving accurate control of patterns, or forming suspended structures. For CMOS, the wet etching is often used to remove thin films, such as hard mask materials (e.g., Si-oxide, Si-nitride, etc.). CMOS process pays less attention to anisotropic wet etching technique but more attention on the selectivity of etchants to different materials. Compared with CMOS process, the largest difference in the dry etching for MEMS technology is the etching depth (1–100 um scale) and the etching depth-width ratio. For CMOS process, dry etching is often used for patterning with smaller etching thickness (nm scale) and etching depth-width ratio, but the requirement of morphology, accuracy, uniformity, and selectivity are very high.