Micromanufacturing and Fabrication of Microelectronic Devices
Micromanufacturing and Fabrication of Microelectronic PART Devices •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••V The importance of the topics covered in the following two chapters can best be appreciated by considering the manufacture of a simple metal spur gear. It is impor- tant to recall that some gears are designed to transmit power, such as those in gear boxes, yet others transmit motion, such as in rack and pinion mechanisms in auto- mobile steering systems. If the gear is, say, 100 mm (4 in.) in diameter, it can be produced by traditional methods, such as starting with a cast or forged blank, and machining and grinding it to its final shape and dimensions. A gear that is only 2 mm (0.080 in.) in diameter, on the other hand, can be difficult to produce by these meth- ods. If sufficiently thin, the gear could, for example, be made from sheet metal, by fine blanking, chemical etching, or electroforming. If the gear is only a few micrometers in size, it can be produced by such tech- niques as optical lithography, wet and dry chemical etching, and related processes. A gear that is only a nanometer in diameter would, however, be extremely difficult to produce; indeed, such a gear would have only a few tens of atoms across its surface. The challenges faced in producing gears of increasingly smaller sizes is highly informative, and can be put into proper perspective by referring to the illustration of length scales shown in Fig. V.1. Conventional manufacturing processes, described in Chapters 11 through 27, typically produce parts that are larger than a millimeter or so, and can be described as visible to the naked eye.
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