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TWENTY-FIVE years ago, the computing equivalent of today's laptop was a room full of computer hardware and a cartload of punch cards.
Since then, computers have become much more compact and increasingly powerful largely because of lithography, a basically photographic process that allows more and more features to be crammed onto a computer chip. Light is directed onto a mask-a sort of stencil of an integrated circuit pattern-and the image of that pattern is then projected onto a semiconductor wafer covered with light-sensitive photoresist. Creating circuits with smaller and smaller features has required using shorter and shorter wavelengths of light.
However, current lithography techniques have been pushed just about as far as they can go. They use light in the deep ultraviolet range- at about 248-nanometer wavelengths-to print 150- to 120-nanometer-size features on a chip. (A nanometer is a billionth of a meter.) In the next half dozen years, manufacturers plan to make chips with features measuring from 100 to 70 nanometers, using deep ultraviolet light of 193- and 157-nanometer wavelengths. Beyond that point, smaller features require wavelengths in the extreme ultraviolet (EUV) range. Light at these wavelengths is absorbed instead of transmitted by conventional lenses. The result: no light, no image, no circuit.
Semiconductor manufacturers are, therefore, at a critical juncture. Soon, they must decide which lithographic horse to back in the race to the next generation of microchip manufacturing. There are currently four possible alternatives: EUV, x-ray, electron-beam, and ion-beam lithography.
Creating a Virtual Laboratory
Two years ago, three Department of Energy national laboratories-Lawrence Livermore, Lawrence Berkeley, and Sandia/California-formed the Virtual National Laboratory (VNL) to research and develop extreme ultraviolet lithography (EUVL) technology. The VNL is funded by the Extreme Ultraviolet Limited Liability Company-a consortium of Intel Corporation, Motorola Corporation, Advanced Micro Devices Corporation, and Micron Technology, Incorporated- in one of the largest cooperative research and development agreements within the Department of Energy. The three-year, $250-million venture is dedicated to developing the EUVL technology for commercial manufacturing of computer chips and to move this technology into production facilities in the first decade of the 21st century.
Each national laboratory brings unique contributions to this effort. Lawrence Livermore supplies its expertise in optics, precision engineering, and multilayer coatings. Sandia provides systems engineering, the photoactive polymer thin film exposed by the light, and the light source. Berkeley contributes its Advanced Light Source capability to generate EUV light to characterize optics and resists at the nanometer scale.
The VNL's lithography system uses mirrors to project the image of a reflective mask onto the photoresist-coated semiconductor wafer. Ultimately, this system will enable a microchip to be manufactured with etched circuit lines smaller than 100 nanometers in width, extendable to below 30 nanometers. The resulting microprocessors would be a hundred times more powerful than those made today. Memory chips would be able to store a thousand times more information than at present.
"Lithography is generally viewed as the enabling technology for each new generation of semiconductor devices," says Don Sweeney, Lawrence Livermore's program manager for EUVL. "To put this technology into production facilities in 10 years, we need to show that the technology can work under real manufacturing conditions."
The VNL's current focus is on building and integrating the necessary technologies into an engineering test stand (ETS). Each national laboratory spearheads specific development areas for the ETS and for the systems beyond. Lawrence Livermore is leading the efforts to develop the optical systems and components, thin films, masks, and submicrometer metrology required for EUVL. |