A Novel Maskless Post-CMOS Bulk Micromachining Process
This work describes a new post-CMOS (Complementary Metal Oxide Semiconductor) bulk micromachining process for fabrication of various microstructures. The important feature of the post-CMOS process is the use of wet etching without an addition mask, to form various microstructures and deep cavities in the silicon substrate. The post-CMOS process starts with wet etching to remove sacrificial layers, which are stacked layers of metals and vias, to expose the silicon substrate. Then, KOH or TMAH solution is employed to etch the silicon substrate to form various deep cavities and suspended structures. Many suspended structures, which include beams, bridges and plates, are fabricated using the standard 0.35-μm SPFM (Single Polysilicon Four Metal) CMOS process and the post-CMOS process. Experimental results reveals that a plate with an area of 200×200 μm2, a bridge with a length of 300μm, and various beams with lengths from 100-μm to 400-μm suspended on a deep cavity were fabricated successfully.