Pinpointing sources of computer chip dust.

• Position: Lasers - Brief Article

Engineers at Purdue University, West Lafayette, Ind., have demonstrated concepts that could eventually save computer chip manufacturers millions of dollars in downtime every year by using lasers to identify and pinpoint the sources of contaminating dust and other defects quickly. Semiconductor manufacturers already use lasers to detect dust particles on expensive silicon wafers, which contain hundreds of chips, but then the manufacturing operation must be shut down while workers try to determine what the dust particles consist of and where they came from, especially when large quantities are found. The source of the dust must be eliminated before production can resume. If an electron microscope is needed to trace the dust, the contaminated wafer essentially is destroyed in the process, adding to the loss.

Each 300-millimeter wafer, roughly 12 inches in diameter, can yield 200 chips, which eventually might be worth nearly $1,000,000. If a new wafer rolls off the line every minute, one hour of downtime can cost tens of millions of dollars.

"It would be a huge advantage if you could identify the contaminant and its source in addition to just detecting it during the in-line laser inspection process," indicates E. Dan Hirleman, head of the university's School of Mechanical Engineering. "As the features in circuits are getting smaller every 18 months or so, the size of a killer defect is getting smaller and smaller. One way to rapidly detect and identify smaller defects is to use laser beams of shorter wavelengths, such as in the deep ultraviolet range." The same lasers used to detect dust might be utilized to identify the particles and begin tracing the contamination source within seconds.

Because circuits in new computer chips are only slightly wider than the particles, the contaminants are large enough to ruin or short-circuit the tiny "wires" in the chips. New...