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Definition: wafer

(1) A small magnetic tape cartridge in the early 1980s. See Stringy Floppy.

(2) The base unit of chip making. A wafer is a slice taken from a salami-like silicon crystal ingot up to 300 mm (11.8") in diameter. The larger the wafer, the more chips produced in a single production pass, which comprises a series of photomasking, etching and implantation steps. Wafers are approximately 1/30th of an inch thick; however, the actual layers of transistors that make up the active circuitry are only a few microns deep (see active area).

Wafers started out from one to three inches in diameter. Then came 100 mm ingots (3.9"), followed by 125 mm (4.9"), 150 mm (5.9"), 200 mm (7.9") and 300 mm (11.8"). The much larger 450 mm (17.7") wafer has yet to catch on due to the huge investment in new machinery. See chip, chip manufacturing, transistor and wafer scale integration.

The Boule Is Sliced
The silicon ingot, which is known as a "boule," is sliced into wafers. (Image courtesy of IBM.)

Different Sizes
From top to bottom, the wafers are 150, 200 and 300 mm (5.9", 7.9" and 11.8") in diameter. (Images from top to bottom courtesy of Texas Instruments, Inc., Advanced Micro Devices, Inc. and Intel Corporation.).

Heating the Wafers
The red glow comes from a furnace that reaches 1000 degrees centigrade. The semiconductor wafers are baked in the oven to prepare them for the chip-making process. (Image courtesy of Intel Corporation.)