Bulk micromachining

A common device for limiting the range of an etchant is a so-called 

The structure of a MEMS device typically involves a part that has been micromachined from a wafer integrated with other components to result in a three-dimensional configuration. A technique for integration of components with basic planar geometry is wafer bonding, usually achieved by pretreatment of the wafer to assure planarity and cleanliness, followed by a high temperature anneal with the surfaces to be bonded in firm contact. 

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Fig. 2.71a-c Bulk micromachining etch profiles. Reprinted from Kandlikar and Grande (2002) with permission... 

Tu, J. K., Huen, T., Szema, R., Ferrari, M., Filtration of sub-100 nm particles using a bulk-micromachined, direct-bonded silicon filter, J. Biomed. Microdevices 1 (1999) 113-119. 

Problems of Anisotropic Bulk Micromachining Convex-corner Underetching... 

Electrochemical etching is one way of controlling the etch rate and determine a clear etch stop layer when bulk micromachining Silicon. In this case, the wafer is used as anode in an HF-Electrolyte. Sufficiently high currents lead to oxidation of the silicon. The resulting oxide which is dissolved by the HF-solution. Since lowly doped silicon material is not exhibiting a notable etch rate, it can be used as an etch stop. 

D Processing Technology 200 Sensors, Actuators and Passive Components 201 Bulk Micromachining Technology 201 Surface Micromachining of Silicon 205 Summary 205... 

C. Dilcso, E. Vazsonyi, M. Adam, I. Szabo, I. Bdrsony, J.G.E. Gardeniers, and A. van den Berg. Porous silicon bulk micromachining for thermally isolated membrane formation . Sensors and Actuators A60 (1997), 235-239. 

Wensink, H., Elwenspoek, M.C., New developments in bulk micromachining by powder blasting. Micro Total Analysis Systems, Proceedings 5th p7AS Symposium, Monterey, CA, Oct. 21-25, 2001. Kluwer Academic Publishers, Dordrecht, the Netherlands, 2001, 393-394. 

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. 

Substrates The substrates in microelectronics are mainly Si wafers. For mobile applications, silicon-on-insulator (SOI) wafers increasingly replace bulk Si wafers and for very specific high-frequency applications, III-V compound semiconductors (e.g., GaAs) are used. The majority of substrates in microfabrication are Si wafers, but metal, glass, and ceramic substrates are also common. Particularly when using glass, quartz, and ceramic wafers in CMP processes, it has to be taken into account that they are brittle and easy to break. The situation is worse when the material is also under stress induced by deposited layers. For applications where the backside of the wafer has to be structured (e.g., in bulk micromachining), double-side polished substrates are employed. 

SiN mask for KOH etching FIGURE 14.1 Schematic of integrated pressure sensor in bulk micromachining. 

Dticso, C., V sonyi, E., Szabo, L, Barsony, L, Gardeniers, J.G.E., and Van den Berg, A., Porous silicon bulk micromachining for thermahy isolated membrane formation. Sens. Actuators, A, 60, 235, 1997. 

R. R. A. Syms, B. M. Hardcastle, and R. A. Lawes, Bulk micromachined silicon comb-drive electrostatic actuators with diode isolation, Sensors Actuators A 63, 61, 1997. 

D. Eichner and W. von Munch, A two-step electrochemical etch-stop to produce freestanding bulk-micromachined structures, Sensors Actuators A 60, 103, 1997. 

A representative example in which glass-to-silicon bonding is used are bulk micromachined accelerometers [121]. In this case, glass serves several functions ... 

Two distinctive ways of patterning a material in an axis perpendicular to the substrate surface are digging in the substrate (i.e., bulk micromachining) and building up starting from the substrate surface (i.e., surface micromachining, which is discussed in Section 5.2 of this book). 

Bulk micromachining relies on several etching techniques and creates projections of planar photolithographic masks in 3 dimensions. Surface micromachining relies on sacrificial layer and wafer bonding techniques. It creates true 3D structures as a stack of 2D patterned layers. Hence, it is more correct to refer to both micromachining techniques as two and a half dimensional (2% D). 

Bulk and surface micromachining are complementary techniques, and hence, using them in combination produces the most versatile devices [5]. The development of SOI wafers [6] offered such a combination, allowing the production of typical surface-micromachined structures by employing only bulk micromachining. 

Fig. 5.1.12 Representative bulk-micromachined structure made from SOI wafers by anodic bonding...

Figure 5.1.12 shows a typical bulk-micromachined structure fabricated on an SOI wafer by use of the previously described etching and bonding techniques. 

To show the strength and varied possibilities of bulk micromachining, some examples used in automotive products are presented in this section. 

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