| TECHNOLOGY |
A Cooperative Research & Development Agreement between LANL and SC Fluids led to the development of SC Fluids' Arroyo System, a machine that automates the process. Arroyo is now being evaluated in the semiconductor industry. The fabrication of integrated circuits relies on multiple-step photolithography to define the shape and pattern of individual circuit features. Current chip manufacturing primarily uses wet chemical processing involving hydroxylamines, mineral acids, and organic solvents at various stages. In the process, a copious amount of ultrapure deionized water is needed for rinsing. Chip fabrication plants thus consume thousands of gallons of chemicals and generate some 4 million gal of wastewater in a typical day. A large amount of isopropyl or other alcohol also is used as a drying solvent. Arroyo uses supercritical CO2 with small amounts of benign cosolvents, such as 1 wt % propylene carbonate, according to Laura B. Rothman, SC Fluids' vice president for technology. The semiconductor device to be stripped or cleaned is first "soaked" for a few minutes in the supercritical CO2/cosolvent mixture to soften and loosen the photoresist. Pressure pulsing then creates turbulence to dislodge and remove the resist. A final "rinse" with pure supercritical CO2 removes any remaining debris and residual propylene carbonate. A drying step is not needed, and the inexpensive CO2 and propylene carbonate can be recycled. The name Arroyo derives from SC Fluids' staff working with researchers at LANL in New Mexico. "We were influenced by the Southwest," Rothman says. "Arroyo is by definition 'a deep gully cut by an intermittent stream; a dry gulch.' We creatively interpreted this as a 'dry wash' for naming our machine." Overall, SCORR simplifies and streamlines the integrated circuit manufacturing process, resulting in large cost savings and a lower burden on the environment, Rothman notes. The technical merit of using supercritical CO2 is equally important to the environmental benefits, she adds. Supercritical CO2's very low surface tension and gaslike viscosity will be able to continue doing the job of cleaning wafer surfaces as deep or narrow architectures become ever smaller, Rothman says. Existing wet chemical stripping technology, however, will eventually be limited by the physical properties of the liquids. |
| UPDATE | 07.02 |
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