Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

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12.15 Semiconductor Devices • 495

Inexpensive microelectronic circuits are mass produced by using some very inge-

nious fabrication techniques. The process begins with the growth of relatively large

cylindrical single crystals of high-purity silicon from which thin circular wafers are

cut. Many microelectronic or integrated circuits, sometimes called “chips,” are pre-

pared on a single wafer. A chip is rectangular, typically on the order of 6 mm (^14 in.)

on a side and contains millions of circuit elements: diodes, transistors, resistors,

and capacitors. Enlarged photographs of microprocessor chips at different magni-

fications are presented in Figures 12.27aand 12.27b; these micrographs reveal the

intricacy of integrated circuits. At this time, microprocessor chips containing over

one billion transistors are being produced, and this number doubles about every

18 months.

Figure 12.27 (a) Scanning electron

micrograph showing a small region of a

microprocessing chip (a 0.5-MB selected

address device). The narrow, white regions are

an aluminum top layer that serves as the

wiring for this device. The gray regions are

diffusion-layer doped silicon that have been

coated with an interlayer dielectric.

Approximately 2000×.(b) An optical

photomicrograph showing a portion of a

circuit that is used to test microprocessing

chips. The narrow, light regions are aluminum

connectors, and the white, square areas are

test pads (semiconductor devices); test circuits

(also composed of semiconductor devices)

appear in the upper left-hand corner of the

photograph. Approximately 50×. (Both

photographs courtesy of National

Semiconductor Corporation.)