FEB. 9 Los Alamos, New Mexico–A new photoresist removal technology that eliminates the use of hazardous chemicals and the production of wastewater in the fabrication of ICs has been created by scientists at the U.S. Department of Energy’s Los Alamos National Laboratory (LANL) in New Mexico. This is important, because an estimated 4 million gallons of wastewater are produced and thousands of gallons of corrosive hazardous materials are used on an average day of operations at a chipmaking plant.
The technology, known as “SCORR,” focuses on photoresist removal, where high intensity light is combined with aggressive acids and corrosives to create ICs.
“Carbon dioxide becomes critical at pressures above 1,050 pounds per square inch and temperatures above 31 degrees centigrade,” explains Craig Taylor, of LANL’s SCORR team. “In its supercritical phase, the gas becomes liquid but behaves a little like both–giving it the ability to act as a solvent. But supercritical carbon dioxide alone is somewhat ineffective, so it is combined with minor amounts of a more effective co-solvent, and we’ve seen that this mixture is quite effective at photoresist removal. On top of that, when the pressure and temperature are lowered, the supercritical carbon dioxide returns to its gas phase, leaving the silicon wafer bone-dry and virtually free of any dirt–eliminating the need to rinse with ultrapure water and dry with isopropyl alcohol.”
The LANL photoresist removal technology produces virtually zero hazardous waste. Its closed-loop system reuses the carbon dioxide, releasing no greenhouse gases to the atmosphere. The additive co-solvents are easy to separate from the mixture, because of their low vapor pressure, and are collected and reused.
“Even if you were to set aside the hazards and pollution associated with the corrosive materials used in chipmaking, you still have the issue of water use, which is especially critical in the Southwest where several large chip fabrication facilities are located,” Taylor says. “We believe that the supercritical carbon dioxide process has the potential to save hundreds of millions of gallons of water every year, even if it were installed in just one factory.”
The early work on this technology was accomplished through a Cooperative R&D Agreement with Hewlett Packard, and now continues with IBM and GT Equipment Technologies, Inc.