National Geographic : 1982 Oct
making a chip HUMBLE BASE of the chip, and earth's most abundantelement after oxygen, silicon is refined from quartz rocks (below), such as these in a North Carolina quarry. Silicon's propertiescan be altered to create electronic switches, or transistors, that control and amplify electricalsignals. Cutaways below show major steps in transistorfabrication. Melted and grown into long crystals, purified silicon is sliced into wafers (i) on which chips are made, hundreds at a time. Each may hold hundreds of thousands of microscopic transistors. Wafers are insulated with a film of oxide (tan), then coated with soft light-sensitive plastic called photoresist (purple). Masked by a stencil and flooded with ultravioletlight (2), exposed photoresisthardens into the proper outline. Acids and solvents strip away unexposed photoresist and oxide, baring the patterned silicon to be etched by superhot gases (3), a technique used at IBM's Thomas J. Watson Research Center (right).More silicon is laid down, masked, and stripped (orange,4), then implanted with chemical impurities, or dopants (green), thatform negative and positive conductingzones (5). Repeating these steps builds layers (6) linked by connecting "windows." Metal, often aluminum (blue), is condensed onto the wafer, filling these gaps andforming conductingpathways (7). Each chip (red square, 8) with its transistorsis diced from the wafer and bonded with conventionalwires, seen twice actualsize in this Synertek, Inc., chip (below, far right).