Anisotropic Silicon Micromachining

Anisotropic silicon micromachining Bulk micromachining of silicon... 

Bulk micromachining of silicon Anisotropic silicon micromachining... 

A planar substrate, such as silicon wafer, could be micromachined by a sequence of deposition and etching processes. This results in three-dimensional microstructures which can be implemented in cavities, grooves, holes, diaphragms, cantilever beams etc. The process referred to as silicon micromachining often employs anisotropic etchants such as potassium hydroxide and ethylene diamine pyrocatechol. The crystallographic orientation is important as the above-mentioned etchants show an etch-rate anisotropy. The ratio for the (100)-, (110)- and (111)- planes is typically 100 16 1. The technique of electrochemical etch stop could be applied for control of the microstructural dimensions. An alternative... 

Silicon Micromachining, Fig. 2 Schematic of cross-sectional view of anisotropically etched microchannels (a) in (100) silicon and (b) in (110) and (c) of 3-D aerial view of anisotropically etched microchannels in (100) silicon using wet chemical etchants of KOH, EDP, or TMAH... 

Silicon has a diamond cubic crystal structure. The Miller indices of the main crystallographic planes of silicon are (100), (110) and (111), respectively. In the wet bulk-micromachining, there are two silicon etching methods isotropic (direction-independent) and anisotropic (direction-dependent) etching. Wet chemical etching solutions are used in this bulk silicon micromachining technology. 

Bulk micromachining Microfabrication of three-dimensional features such as membranes, cavities, and so on by anisotropic dry or wet etching into the bulk of substrate materials like silicon, quartz, or others. 

D. Kendall, A new theory for the anisotropic etching of silicon and some underdeveloped chemical micromachining concepts, J. Vac. Sci. Technol. A8, 3598, 1990. 

Bulk Micromachining, Fig. 3 Typical structures which can be fabricated in single-crystal silicon using the anisotropic etching technique... 

The anisotropic wet etching of silicon is a unique fabrication process in the MEMS field. The need to develop new processes to fabricate functional 3D microstructures in various materials is urgent for progress in microfluidic systems, microsensors, micro-actuators, and microinstrumentation. At present, to integrate surface micromachined devices and standard IC devices with bulk micromachined structures to demonstrate a new functional MEMS application is still a challenge for researchers who work in this field. The cooperation of multidisciplinary researchers will be required to develop miniature systems with the most appropriate building philosophy and the best operation performance. 

Kendall DL (1990) A new theory for the anisotropic etching of silicon and some underdeveloped chemical micromachining concepts. J Vac Sci Technol A 8(4) 3598-3605 Kittisland G et al (1990) A sub-micron particle filter in silicon. Sens Actual A21-3 904-907 Klima O et al (1993) Transport properties of self-supporting porous silicon. J Non-Cryst Solid 164-166 961-964... 

Wet bulk micromachining was first developed in the Bell Telephone Laboratories in the mid-1960s. Anisotropic etching of silicon was achieved in a wet chemical solution composed of KOH, alcohol and water. Bulk micromachining using chemical and electrochemical etching processes... 

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