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Sematech reports progress on EUV litho for 22nm

Posted: 14 Aug 2008 ?? ?Print Version ?Bookmark and Share

Keywords:22nm? EUV lithography? extreme ultraviolet?

Sematech has disclosed a way of using extreme ultraviolet (EUV) lithography to define silicon devices with a half-pitch resolution as small as 22nm. The chip research consortium says the work shows the promise of EUV to serve a future 22nm semiconductor node. Sematech is also close to defining features smaller than 20nm.

Engineers have been racing to develop ways to create devices for a 22nm semiconductor technology, just two generations beyond the 45nm process, which Leading chipmakers, such as Intel Corp., are using for their microprocessors today. As recently as last month's Semicon West conference, speculation was rising that EUV would not be ready for the 22nm node, fueling work on extending a double-patterning lithography being developed for the 32nm node.

Sematech announced Aug. 12 it has worked with major resist suppliers to demonstrate a chemically-amplified EUV resist platform that supports 22nm half-pitch resolution. The group said it is "close to resolving" sub-20nm half-pitch features.

"Enabling 22nm half-pitch resist goes a long way towards enabling the technology as a whole," said Stefan Wurm, program manager for EUV at Sematech in an email exchange.

"These results mark a cornerstone in the development of EUV lithography," said John Warlaumont, VP of advanced technology at Sematech, in a prepared statement. "They represent the first real 22nm resist data, building confidence for EUV as a viable technology for 22nm half-pitch lithography," he added.

Overcome EUV litho challenge
The Sematech results showed an acceptable photospeed (at 15mJ/cm?), but line width roughness at 5- to 6nm was higher than specified in the International Technology Roadmap for Semiconductors (ITRS), the industry's chip roadmap. Sematech expects that resist post processing and etch processes are likely to bring down roughness down to a value that is acceptable for early adopters in DRAM and flash memory chips.

The trade-off between resist resolution, line width roughness and photospeed is one of the key challenges that need to be overcome to enable EUV lithography, said Wurm.

"This achievement [of a 22nm demo] was deemed to be impossible by leading resist experts only a few years ago," said Chawon Koh, an EUV resist process engineer leading the joint evaluation of resist platforms between Sematech and resist suppliers.

Koh attributed the advance in part to the use of micro-exposure tools at located at the University at Albany's College of Nanoscale Science and Engineering and at University of California at Berkeley. The new tools helped researchers at Sematech's EUV Resist Test Center in Albany, demonstrate a 35nm half-pitch resolution barrier in 2006 and a 26- to 28nm half-pitch devices more recently.

Meeting the deadline
The EUV resist work is just one piece of the puzzlealbeit an important oneneeded to deliver a fully 22nm process node. Due to delays in delivering all the parts of the complex technology, some developers have raised concerns EUV lithography may not be fully ready for commercial use until a 16nm node, forcing engineers to extend methods currently planned for the 32nm process.

The ITRS roadmap targets volume manufacturing of 22nm half pitch technology by 2016, although some chip makers are likely to start using the technology sooner. To take resists from the development phase to manufacturing "takes a long time" especially if new resist platforms are required, Wurm said in the email exchange.

Outside EUV, Sematech has programs in extensions to existing 193nm immersion lithography. The group is also evaluating or monitoring alternative technologies such as nanoimprint and maskless lithography, he said.

"The focus of Sematech's EUV resist development program is to engineer platforms to realize 22nm high pitch introduction and provide a fundamental understanding of EUV resist exposure mechanisms to develop new platforms," said Wurm in the Sematech press statement. "We believe this two-pronged approach will drive resist development to the highest level and support EUV introduction."

- Rick Merritt
EE Times

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