Scientists develop cleaner method for making computer chips

The new technology focuses on one particular step in the chip manufacture process, ‘photoresist removal’, in which high intensity light combined with strong acids and corrosives are used to alter the topography of a silicone wafer, requiring considerable quantities of ultra-pure water to wash away the solvents. Currently, it is estimated that on an average day at a chip-making plant, four million gallons of wastewater are produced, and thousands of gallons of corrosive hazardous materials, such as hydrochloric and sulphuric acids, are used, say the Los Alamos team.

Instead of using these chemicals, the new technology uses liquified carbon dioxide at a high temperature (above 31°C) and pressure (greater than 1,050 pounds per square inch), termed supercritical carbon dioxide (SCCO2), which acts like a solvent. When used in combination with minor amounts of a cosolvent, SCCO2 has been demonstrated to be a viable and inexpensive alternative, say the researchers.

“On top of that, when the pressure and temperature are lowered the SCCO2 returns to its gas phase, leaving the silicon wafer bone-dry and virtually free of any dirt, eliminating the need to rinse with ultra-pure water and dry isopropyl alcohol,” said Craig Taylor, SCORR team leader. “And the best news, carbon dioxide is cheap, non-flammable, non toxic, biodegradable, recyclable, and plentiful.” Both the added cosolvents and the carbon dioxide are collected and reused without permitting any emissions into the environment.

“We want to bring this technology to the attention of the computer industry, as well as the public in general, just to emphasise the environmental advantages of SCCO2,” said Taylor. “Even if you were to set aside the hazards and pollution associated with the corrosive materials used in chip making, you still have the issue of water use – and that’s especially critical in the south west where several large chip fabrication facilities are located. We believe that the SCCO2 process has the potential to save hundreds of millions of gallons of water every year even if it were installed in just one factory, making it not only a very important technological advance, but an environmental advance, as well.”