Presidential Green Chemistry Challenge: 1997 Small Business Award
Legacy Systems, Inc.
ColdstripTM, A Revolutionary Organic Removal and Wet Cleaning Technology
Innovation and Benefits: During manufacture, silicon-based semiconductors and flat-panel displays require cleaning to remove manufacturing residues, usually with corrosive acid solutions. Legacy Systems developed the ColdstripTM process, which uses only water and oxygen to clean silicon semiconductors. ColdstripTM has the potential to cut the use of corrosive solutions by hundreds of thousands of gallons and also save millions of gallons of water each year.
Summary of Technology: For over 30 years, the removal of photoresists with Piranha solutions (sulfuric acid, hydrogen peroxide, or ashers) has been the standard in the semiconductor, flat panel display, and micromachining industries. Use of Piranha solutions has been associated with atmospheric, ground, and water pollution. Legacy Systems, Inc. (LSI) has developed a revolutionary wet processing technology, ColdstripTM, which removes photoresist and organic contaminants for the semiconductor, flat panel display, and micromachining industries.
LSI's ColdstripTM process is a chilled-ozone process that uses only oxygen and water as raw materials. The active product is ozone, which safely decomposes to oxygen in the presence of photoresist. Carbon dioxide, carbon monoxide, oxygen, and water are formed. There are no high temperatures, no hydrogen peroxide, and no nitric acid, all of which cause environmental issues.
The equipment required for the chilled-ozone process consists of a gas diffuser, an ozone generator, a recirculating pump, a water chiller, and a process vessel. The water solution remains clear and colorless throughout the entire process sequence. There are no particles or resist flakes shed from the wafer into the water; therefore, there are no requirements for particle filtration.
Using oxygen and water as raw materials replacing the Piranha solutions significantly benefits the environment. One benefit is the elimination of over 8,400 gallons of Piranha solutions used per year per silicon wet station and over 25,200 gallons used per year per flat panel display station. Additionally, the overall water consumption is reduced by over 3,355,800 gallons per year per silicon wafer wet station and over 5,033,700 gallons per year per flat panel display station. The corresponding water consumption in LSI's process is 4,200 gallons per year and there is no Piranha use.
In 1995, the U.S. Patent Office granted LSI Patent 5,464,480 covering this technology. The system has the lowest environmental impact of any wet-resist-strip process, eliminating the need for thousands of gallons of Piranha chemicals and millions of gallons of water a year.
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