Cleaning system ensures one swell FOUP
By HANK HOGAN
AUSTIN, Texas—Like many involved with contamination control, Bob Groves, project leader at International Sematech, worries about what he can't see because he knows what you can't see can kill your product.
As the semiconductor industry moves into production of 300-mm wafers, Groves and others are concerned with particles that measure much less than 1 µm. With the new wafer size comes new technology, specifically a healthy dose of robotics, automation and the Front Opening Unified Pod (FOUP).
FOUPs seal wafers in and keep contaminants out, providing protection as wafers travel from station to station. But these new wafer carriers aren't an unmitigated blessing.
"When compared to 200-mm wafer carriers, the design and construction of 300-mm wafer carriers present unique challenges to cleaning them effectively," remarks Groves.
Sematech recently installed a TFC-802 FOUP cleaning system from Technovision, Inc. (Kawagoe, Japan). The company makes a variety of cleaning products for the semiconductor and flat panel display industries. According to Groves, Sematech plans to use the cleaning system in an attempt to head off potential contamination problems.
Made of a combination of transparent and opaque antistatic plastic, FOUPs consist of a wafer carrier, which is either attached to or molded from the surrounding shell. A lid—the front opening part of the FOUP—attaches to and seals the shell. Groves notes that it's the gap between the wafer carrier and the shell that presents the most cleaning problems. This small area is surrounded with plastic on all sides but one, so it's difficult to send water and cleaning agents down into the gap with enough force to dislodge contaminants.
A number of products are intended for FOUP cleaning that are used in existing manufacturing lines at the beginning of the production cycle. Particle counter tests indicate that, for the most part, FOUPs stay clean throughout a manufacturing run. But not all wafer carriers encounter normal, uneventful tours of duty. A few suffer catastrophe. It's these abnormal events that pose the most contamination-control problems for FOUPs. One arises when 300-mm wafers, which are thin silicon disks one foot across, break inside the carrier.
"If somebody breaks wafers in one of these, then all bets are off," says Groves. So, Sematech plans to evaluate the performance of Technovision's cleaning system, which uses deionized water heated to 40 to 50 degrees Centigrade and pressurized to 0.5 megaPascals. The evaluation will be done with surface particle analyzers, witness wafers and liquid particle counters. Results will guide additional system tuning and tests.