Inter-CMOS process for monolithic integrated MEMS resonator

In this work, novel processes for the simultaneous fabrication of the MEMS (micro electro mechanical system) and CMOS (complementary metal oxide semiconductor) components on a monolithic integrated micro-cantilever resonator are proposed. A universal cavity shared by the entire MEMS unit is designed, which decreases the altitude difference between the MEMS and CMOS parts, thus benefiting the subsequent lithography for metal interconnection. The substrate for the CMOS unit is independent on the MEMS unit, assuring electrical isolation. Furthermore, an additional step of selectively removing silicon nitride (Si₃N₄) capping layer and polysilicon (poly-Si) layer upon the CMOS area is added to lower the stress in the MOSFET channel regions. The fabrication of this resonator with on-chip circuits according to the presented inter-CMOS process is investigated first by theoretical analysis, and then moving to experimental verification.