EUV Plows Ahead — Regardless

When it comes to extreme ultraviolet (EUV) lithography, there have long been the never-say-die champions of the technology (with Intel leading the way), and there have been the naysayers (particularly from the nanoimprint camp). But despite the progress that has been made in EUV technology, there seem to be a quickly growing number of industry experts who are willing to speak out against EUV viability. It has become a fiercely political battle, with many of the industry's brightest minds jumping ship rather than be forced to continue to work on a technology that makes little sense to them.

It was only about a year ago — shortly after ASML delivered EUV alpha demo tools to IMEC and Albany NanoTech — that ASML's Martin van den Brink was hailing EUV lithography as "the only real opportunity to scale to 32 nm."¹ Whether or not that was true a year ago, it certainly is not true today. It is widely considered that EUV will no longer be needed for 32 nm production, even if it were able to achieve that goal. Cymer acknowledged as much in its SEMICON West 2007 press release, in which it was announced that ASML would use Cymer as its high-power EUV source provider. In a statement, Bob Akins, Cymer's co-founder and CEO, said, "Together with ASML, Cymer is committed to commercializing EUV source technology to ensure the availability of sub-32 nm exposure tools."

If EUV lithography doesn't see real action until the 22 nm mark, there's a distinct possibility that it will becomes a one-node technology — something this industry has always shied away from. And there are certainly alternatives — perhaps the most promising of which is 193 nm immersion lithography with some sort of double patterning scheme. Combine that with extremely high numerical apertures (NAs) helped along by high-index fluids and other materials, and CMOS scaling may have already seen its final wavelength introduction.

Not surprisingly, folks in the nanoimprint camp still do not speak highly of EUV. At SEMICON West 2007, representatives of imprint toolmaker Molecular Imprints detailed many of the difficulties EUV is facing. The meeting was arranged by John Doering, who said he left ASML for Molecular Imprints specifically because of ASML's dogged focus on EUV lithography, and the unwillingness to spend any time or money exploring what he saw as the more sensible nanoimprint approach. Mark Melliar-Smith, CEO of Molecular Imprints, wondered aloud why chipmakers would want to use a technology that wasn't likely to take them very far. "I don't think EUV can get down to 10 nm," he said.

But even apparent EUV proponents have been frustrated with the lack of workable EUV solutions lately. Speaking with Semiconductor International News Editor David Lammers at SEMICON West 2007, Ludo Deferm, vice president of business development at IMEC, said the discharge-produced plasma (DPP) source used on the EUV alpha demo tool at IMEC results in a scanner throughput of only 0.2 wph. "Already, our lithography program partners are asking us to speed things up, but we are limited by the source," Deferm said. "Fortunately, we also have an interferometer-based EUV system that we can also use for resist development, but we need the alpha scanner for masks and other types of EUV development."

ASML now plans to replace the Philips DPP sources of its alpha tools with Cymer's laser-produced plasma (LPP) source for high-volume manufacturing. In a statement announcing ASML's choice of Cymer as its next EUV source supplier, ASML's van den Brink was quoted as saying, "We are confident that Cymer will help us make production-worthy EUV lithography a reality, clearing the way for semiconductor manufacturers to image ever-smaller features on chips."

EUV technology certainly seems to be making some headway lately. Cymer has made great advances in source power and debris mitigation, reaching 50 W with its LPP source and collector lifetimes of about a year (see "Cymer Advances EUV Source to ASML HVM Acceptance "). Europe recently completed its More Moore program, listing several achievements it made in EUV developments.

Yet the industry as a whole seems to lack the confidence that anyone will ever be able to economically make use of EUV lithography. But the political (or whatever) push remains, and uncountable millions of dollars continue to be poured into the technology, while quite likely more feasible, cheaper and less painful solutions lie just outside the industry's reach because there are simply no dollars left to be thrown their way.