Anisotropic silicon etch to house CMOS compatible MEMS microstructures without planarization techniques

The MEMS (Micro-Electro-Mechanical Systems) acronym recalls mechanical structures of micrometric dimensions performing a well-controlled electronically preset function. The real sense of a microelectromechanical system (MEMS) is the interaction of electronic circuits with the mechanical transducers (microstructures) to perform a useful function. However, the MEMS-microstructures require a wide range of thickness according to the particular application, and the resulting topography directly affects the subsequent photolithography steps. Fabrication of a trench as deep as the microstructures thickness using two solutions: TMAH (tetramethyl ammonium hydroxide) and KOH (potassium hydroxide), without the use of planarization techniques is presented. Inside the trench, the microstructures can be fabricated to obtain reliable microelectromechanical systems. It is shown that using TMAH solution the geometries can be placed at the edge of the trench with a good resolution and consistency. This is required for the correct definition of the interconnect lines starting on the surface of the wafer (electronic devices) through the bottom of the trench (mechanical devices/structures).