Etching microelectromechanical systems

The high selectivity of wet etchants for different materials, e.g. Al, Si, SiOz and Si3N4, is indispensable in semiconductor manufacturing today. The combination of photolithographic patterning and anisotropic as well as isotropic etching of silicon led to a multitude of applications in the fabrication of microelectromechanical systems (MEMS). 

Despite the fact that dry etching techniques have improved dramatically in recent decades, the manufacture of microelectromechanical systems (MEMS) is still a domain of wet etching and silicon electrochemistry. The multiplicity of structures that can be achieved with silicon, together with its excellent mechanical properties [Pe6], have led to an immense variety of micromechanical applications. 

MEMS (microelectromechanical systems) are systems with small device sizes of 1-100 pm. They are typically driven by electrical signals. To fabricate such systems materials like semiconductors, metals, and polymers are commonly used. MEMS technology fabrication is very cost-efficient. The structures are transferred by processes, which are applied to many systems on one substrate or even many of them simultaneously. The most important fabrication processes are physical vapor deposition (PVD), chemical vapor deposition (CVD), lithography, wet chemical etching, and dry etching. Typical examples for MEMS are pressure, acceleration, and gyro sensors [28,29], DLPs [30], ink jets [31], compasses [32], and also (bio)medical devices. 

K. R. Williams, K. R. Williams, K. Gupta, and M. Wasihk. Etch rates for micromachining processing-Part II Etch rates for micromachining processing-Part II. Microelectromechanical Systems, Journal of, 12(6) 761-778, 2003. 

Hsieh et al. (1997) employed microelectromechanical system (MEMS) technologies to develop a miniature ECM using polymer electret as show in Fig. 7. The diaphragm is 0.91 pm LPCVD silicon nitride fabricated through backside anisotropic wet etching of <100> silicon substrate. Teflon AF is spun on with the thickness of 1.2 pm over the nitride membrane and is used as the electret layer. After charging, the silicon chip with the diaphragm is bonded to the other silicon chip with a photoresist spacer. 

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