EUV Lithography Makes Serious Progress
Aaron Hand, Managing Editor -- Semiconductor International, 6/1/2001
 |
Part of what makes EUV lithography appealing is the fact that it is an extension of the optical lithography that the industry is already intimately familiar with. But the transition to EUV is nonetheless a significant departure from today's norm, moving from today's standard 248 nm lithography system to use a 13 nm wavelength. So April's demonstration was a milestone along the road to achieving considerably narrower chip features — 70 nm and smaller.
|
|
The prototype machine, called the Engineering Test Stand (ETS), is the result of years of research and development by a collaboration of three U.S. Department of Energy national laboratories and the EUV LLC (which includes Intel, Motorola, AMD, Micron Technology, Infineon Technologies and IBM). Jointly referred to as a Virtual National Laboratory, the three national labs are Lawrence Berkeley National Laboratory, Lawrence Livermore National Laboratory and Sandia National Laboratories, all in California. The prototype stepper was unveiled at a formal ceremony at Sandia (Livermore, Calif.), where it was assembled.
Engineers have been working on the ETS, which measures about 10 × 10 × 10 ft, since the EUV LLC was developed in 1997. To reach prototype status, the team had to overcome several technical barriers. Several research groups have been working on the lightsource itself, competing to gain acceptance. At 13 nm, the lightsource has a wavelength so short that it is absorbed by nearly all materials, making it difficult to develop a mechanism to capture that light.
The system of mirrors used to reduce the mask image to be printed on the wafer requires curved surfaces that are smooth to within the diameter of an atom. To make it more challenging, this had to be done on reflective non-spherical surfaces, and the mirrors had to be coated with 40 layers of pairs of alternating materials only a few atoms thick.
EUV lithography required a new control environment to restrict contamination. Along these lines, producing defect-free masks is particularly challenging at this shorter wavelength. Requirements for superimposing images at various steps are also tight, calling for a precise stage. The prototype uses magnetically levitated stages that glide without friction to nanometer accuracy.
The alpha full-field EUV prototype stepper is the first step to commercializing EUV lithography. The next step, noted Chuck Gwyn, program manager of the EUV LLC, is to transfer that technology to the lithography equipment manufacturers for developing beta and production tools. The ETS will be used by consortium partners and lithography tool suppliers over the next year to refine the technology and to develop prototype machines for high-volume chip manufacturing. Production tools are not expected for at least four years.
Although the ETS was a significant milestone, more lie ahead. Accordingly, more industry players are expected to publicly embrace EUV technology in the near future. IBM Corp. became the most recent company to join EUV LLC just a few months ago, its microelectronics division (IBM Microelectronics, East Fishkill, N.Y.) working with the consortium. And IBM will assuredly not be the last.
For additional information on lithography, go to www.semiconductor.net/lithography
