November 1998

Semiconductor Manufacturing: No Tresspassing

By David Rotman

As computers get smaller and smaller, contamination becomes a bigger issue in manufacturing them. Even the vacuum chambers used in "clean rooms" aren't completely free of wayward particles-and even tiny particles can ruin an expensive set of silicon wafers.

Existing defenses against these trespassers aren't particularly sharp. They work by periodically checking the surfaces of silicon wafers for impurities. These methods are hit-and-miss, and they're helpless against particles smaller than two-tenths of a micrometer.

Now William Reents, a chemist at Lucent Technologies' Bell Labs, has put together a laser-based instrument to zero in on particles as small as one-thousandth of a micrometer, a twohundredfold improvement. What's more, the device can determine in real time the chemical composition of the contamination, helping pinpoint its source.

Reents' invention pulls particles through a thin capillary tube. A laser zaps the particles, ionizing the atoms; the ions are then accelerated toward a detector. The time it takes for each ion to reach the detector depends on the ion's mass, and that information can be used to determine the chemical makeup of the particle.
Tests are under way to see how the detector performs attached to actual clean-room equipment. If all goes well, Bell Labs hopes to entice an equipment maker to produce an instrument rugged enough to stand up to manufacturing conditions.