Salt/Sand Blizzards Threaten Snow-Belt Fabs
By Lisa A. Coleman
Hudson, MA–This winter`s extreme weather has brought its share of headaches to everyone and has caused major and unique problems for many of the nation`s semiconductor fabs. Persistent storms and freezing temperatures have fabs in the Midwest and Northeast facing problems unthought of in Silicon Valley.
Corrosive road chemicals and salt are finding their way into clean facilities, and semiconductor manufacturers are seeking better ways to keep the deadly contaminants out of the fab.
In the Northeast, Digital Equipment Corp. is looking at ways to minimize migration of road sand and salt into its two Alpha chip fabrication facilities in Hudson, Mass. “If it can get into the building, it can get into the fab,” warns Digital`s yield engineering manager, Charlie Gross.
At the Hudson site, Digital`s 333-MHz Alpha chip is manufactured at 0.5 microns in a Class 10 fab which is adjacent to a new 0.35-micron Class 1 cleanroom, where the next-generation Alpha chip will be manufactured. To enter the newer fab, Digital personnel must walk through the other building because the new fab has no direct entrance from the outside. However, the entrance to the other facility is surrounded by sidewalks that are both shoveled and salted.
The salt and sand are being brought into the building caked in the deep-creviced soles of winter boots which people wear for better walking traction, explains Gross. “You wear those boots into the building and the salt doesn`t melt instantaneously. The contaminant just stays in the soles, getting closer and closer to the fab,” Gross says.
Personnel entering Digital`s newer fab must first walk a circuitous route over protective rugs and mats. “That helps get some of the stuff off the shoes and boots,” says Gross. Once in the change rooms, personnel put on building shoes. “We never let the building shoes leave the new building,” adds Gross.
Digital takes precautions to keep shoes free of sand and salt, and also uses black, lint-free wipes to monitor contaminants on the floor. Says Gross: “We`ve found that because [weather] conditions are so bad in the Northeast, road chemicals are actually getting into the clean building, although not into the fab. Still, we know that procedures need to be improved. Since we`ve started using black wipes, we`ve begun to detect contamination closer and closer to the fab. We`re looking into how we can really make this building impenetrable.” The company is contemplating changing the entrance route, changing the entrance itself and possibly incorporating a double shoe change. “We haven`t decided what we`re going to do yet. And, of course, these decisions also get made on the impact of cost and productivity as well as the cleanliness issue.”
To help clean the salt and sand, Digital has increased its janitorial cleaning service this winter. Hallways that lead to the fab area are mopped more frequently, while black wipes are used to verify cleanliness.
IBM Microelectronics (Essex Junction, VT) utilizes a 30-ft. corridor as part of the entrance into its fab. Cleanroom workers stomp sand and salt out of their boots–which is then sucked into drainable floor matting. “People walk over the floor and bang and scrub their boots on this mat. The dirt can then be drained away,” says Dana Watts, architect for Symmes, Maini and McKee Associates, Inc. (Cambridge, MA). A shoe cleaning machine removes the smaller particles not trapped by the mat. Immediately following this process, booties must be donned.
To help control possible road-chemical contamination, Raytheon Co. (Andover, MA) does not use salt to de-ice its roads, the company acknowledges. However, it does use sand, which often gets tracked into the facility. Even with personnel changing from their winter boots into work shoes, it is not always possible to stop sand from coming into the facility.n