Inside a chip factory: silent, clean, precise
Essex Junction, Vt. — Small discs whoosh eerily along pneumatic paths. Technicians, robed in white suits, move silently behind glass partitions. Video screens flash varied abstract patters. Mechanical fingers snatch up small components. And always the air moves -- silently sucked up and scrubbed to almost perfect cleanliness.
"You can't see it now, but under a microscope wonderful colors and patterns appear," says Dick Chapman, IBM's manager of site operations at Essec Junction. He holds what appears to be a small spider up to the morning sun. "The actual chip part is the small dot in the middle. The rest is packaging.
He taps a four-inch, shimmering black disc. "This is the raw material," he says. "Pure silicon."
The cylinder from which the disc came began as a single flawless crystal. Dipped into molten silicon, the seed crystal is spun and slowly pulled out of the crucible -- bringing with it a cylinder with a near-perfect atomic structure.
This discs are sliced off the solid cylinder and coated with a photographic emulsion. Then, a road map of circuitry, enough for dozens of individual chips, is carved on the surface of each disc by exposure to light under a patterned photo mask.
Electricity does not pass easily through pure silicon.To enhance the ability of the silicon to conduct electricity, it is "doped" -- i.e., impurities are injected a few atoms at atime.
The photo-exposure and injection steps are repeated, building up three-dimensional circuitry as much as eight layers thick in pattern more tangled than the most tortuous highway interchange.
Finished discs are "sputtered" -- bombarded with quartz atoms that form a protective layer of glass. Then they are cut into individual chips by lasers or diamond saws. The tiny chips, no more than a few millimeters across, are packaged on a ceramic plate with electrical connections to form the finished product.
In effect, integrated circuits take masses of electronic parts, such as those found inside an old transistor radio, and shrink them down to microscopic size.
As ICs become more complex, experts say, light will be too clumsy a tool for IC production. Light waves can't etch circuit lines enough. As a result, these experts foresee techniques that will "draw" minute circuits with a stream of atoms.