Sep. 22, 1997 LIVERMORE, Calif. - The realization that atomic gas clusters could serve as part of a sort of "light bulb" that emits extreme ultraviolet (EUV) light when laser-heated has inspired a recently patented invention at Sandia National Laboratories. This light source enables research development of EUV lithography to pattern faster, more memory-dense microchips.
Until this invention, synchrotron radiation was the most technically mature alternative for creating EUV light for research lithography systems. Advantages of creating EUV light from laser-heated clusters of xenon gas are that the EUV light that can be gathered and used is potentially brighter than that from a synchrotron (which sprays radiation out in a pinwheel pattern), and the light source takes less space.
In the Sandia invention, a small jet of xenon gas is cooled to temperatures within a few degrees of absolute zero by supersonic expansion into a vacuum. Xenon clusters, in which thousands of atoms are held together by weakly attractive Van der Waals forces, form at these low temperatures. The xenon clusters are heated to about 500,000 degrees Kelvin with pulses of laser light, becoming a plasma. The plasma re-radiates some of this energy, producing EUV light in the process.
Glenn Kubiak, a chemical physicist and Distinguished Member of the Technical Staff in Sandia's Advanced Electronics Manufacturing Technologies Department, received a patent on the laser plasma source invention in November 1996, along with Professor Martin Richardson of the University of Central Florida, who was working on creating laser plasma targets from clusters of water droplets. Kubiak began working on laser plasma sources through the Strategic Defense Initiative program 1987. Sandia began microchip lithography research in 1988. By 1990, Sandia's work on a high-fluence laser plasma source had received an R&D 100 award from R&D magazine. Sandia began a collaboration with AT&T on lithography research in the early 1990s.
"It was a natural collaboration," Kubiak said, "because we already had several years of development of laser-produced plasmas at that time."
In an EUV lithography research program review at Sandia in April 1996, this source of EUV light allowed lithography researchers to meet several technical milestones showing there were no "show-stoppers" to creating a tool for patterning microchips with this shorter wavelength of light. The shorter wavelength allows creating smaller features than possible with the current commercial process that uses visible light.
"The cluster jet was the only thing that could have achieved that in the source area," Kubiak said. Among its advantages are its efficiency at converting the applied laser power to emission of EUV light, and the absence of debris. Creating plasmas from solid laser targets of gold, copper or tin generates debris that coats surfaces of the tool and ruins its ability to image the lithographic features to be patterned at reduced sizes on silicon wafers.
This light source is being integrated into Sandia's laboratory research system capable of printing proof-of-principle, functioning microelectronics devices with EUV lithography. The first fully functional transistor patterned with EUV lithography was created on an earlier research lithography system in 1996.
To further develop EUV lithography with entirely private funding, Sandia is working as part of a Virtual National Laboratory with Lawrence Livermore and Lawrence Berkeley national laboratories. Last week, Department of Energy Secretary Federico Peña announced the labs will receive $130 million over three years for EUV lithography research from an industrial consortium led by Intel Corp., Motorola Corp. and Advanced Micro Devices Inc. The consortium will spend an additional $120 million during that period on EUV lithography development.
Sandia is a multiprogram Department of Energy laboratory, operated by a subsidiary of Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major research and development responsibilities in national defense, energy, environmental technologies and economic competitiveness.
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