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2002 Presidential Green Chemistry Award
SCORR — Supercritical CO2 Resist Remover

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from Presidential Green Chemistry Challenge Award Recipients, p.4-5

The semiconductor industry is the most successful growth industry in history, with sales totalling over $170 billion in the year 2000. The fabrication of integrated circuits (ICs) relies heavily on photolithography to define the shape and pattern of individual components. Current manufacturing practices use hazardous chemicals and enormous amounts of purified water during this intermediate step, which may be repeated up to 30 times for a single wafer. It is estimated that a typical chip-fabrication plant generates 4 million gallons of waste water and consumes thousands of gallons of corrosive chemicals and hazardous solvents each day.

SC Fluids, in partnership with Los Alamos National Laboratory, has developed a new process, SCORR, that removes photoresist and post-ash, -etch, and -CMP (particulate) residue from semiconductor wafers. The SCORR technollogy outperforms conventional photoresist removal techniques in the areas of waste minimization, water use, energy consumption, worker safety, feature size compatibility, material compatibility, and cost. The key to the effectiveness of SCORR is the use of supercritical CO2 in place of hazardous solvents and corrosive chemicals. Neat CO2 is also utilized for the rinse step, thereby eliminating the need for a deionized water rinse and an isopropyl alcohol drying step. In the closed loop SCORR process, CO2 returns to a gaseous phase upon depressurization, leaving the silicon wafer dry and free of residue.

SCORR is cost-effective for five principal reasons. It minimizes the use of hazardous solvents, thereby minimizing costs required for disposal and discharge permits. It thoroughly strips photoresists from the wafer surface in less than half the time required for wet-stripping and far outperforms plasma, resulting in increased throughput. It eliminates rinsing and drying steps during the fabrication process, thereby simplifying and streamlining the manufacturing process. It eliminates the need for ultra-pure deionized water, thus reducing time, energy, and cost. Supercritical CO2 costs less than traditional solvents and is recyclable.

SCORR will meet future, as well as current technology demands. To continue its astounding growth, the semiconductor industry must develop ICs that are smaller, faster, and cheaper. Due to their high viscosity, traditional wet chemistries cannot clean small feature sizes. Vapor cleaning technologies are available, but viable methods for particle removal in the gas phase have not yet been developed. Using SCORR, the smallest features present no barriers because supercritical fluids have zero surface tension and a "gaslike" viscosity and, therefore, can clean features less than 100 nm. The low viscosity of supercritical fluids also allows particles less than 100 nm to be removed. The end result is a technically enabling "green" process that has been accepted by leading semiconductor manufacturers and equipment and material suppliers.

SCORR technology is being driven by industry in pursuit of its own accelerated technical and manufacturing goals. SCORR was initially developed through a technical request from Hewlett Packard (now Agilent). A joint Cooperative Research and Development Agreement between Los Alamos National Laboratory and SC Fluids has led to the development of commercial units (SC Fluids' Arroyo™ System). Other industry leaders, such as IBM, ATMI, and Shipley, are participating in the development of this innovative technology.

May 21/2008

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