SANTA CLARA, Calif.—Much to the chagrin of many backers of extreme ultraviolet (EUV) lithography, the technology's continually slipping target date for insertion into volume production has enabled several other intriguing lithography technologies to hang around the next-generation lithography race, which not long ago was considered all but over.
Most in the lithographer community still expect EUV to overcome remaining technical hurdles and take over for 193-nm optical lithography as the mainstream lithography technology, even if much later than originally hoped. But EUV's stumbles have left the door open for technologies such as nano-imprint lithography, e-beam direct write and the hot newcomer, directed self-assembly (DSA) lithography. Proponents of each believe they could still yet play a role in future chip production, even if EUV assumes the mantle of mainstream production lithography.
"I'm convinced there is a role for several different technologies," said Moshe Preil, manager of emerging lithography and tools, during a panel discussion at the SPIE Advanced Lithography Conference here Tuesday (Feb. 14). "It isn't one size fits all. A lot of it depends on how many wafers you are producing and what device type."
Preil and other panelists see the possibility of some or all of these technologies being used in production as part of a multi-technology strategy. E-beam direct write, for example, could find a role in creating prototype chips, thus saving the cost of building photomasks for products being considered for development. Nano-imprint, which promises superior resolution and no limitations on the types of shapes that can be imaged, could be implemented in memory chip production in the next 18 months, according to S.V. Sreenivasan, chief technology officer at Molecular Imprints Inc., which provides nano-imprint lithography systems.
"I can see at least two or three technologies being used at the same time," Preil said.
But all of the technologies still have significant development challenges to overcome. For e-beam direct write—which has always been enticing to chip makers because of the promise of eliminating the need for buying photomasks—the knock has always been throughput. Papers at SPIE are reporting promising results with multi-beam systems. Earlier this week, French research institute CEA-Leti has said that 22-nm lines and spaces have been created using direct-write e-beam lithography technology and that the demonstrated resolution meets the requirements for both 14- and 10-nm logic processing nodes. Mapper Lithography BV, which supplied the pre-alpha tool that CEA-Leti has been using since 2009 and which also announced the extension of a collaborative R&D program with the French research institute for an additional three years, said it would complete its Matrix pre-production platform this year, with initial throughput of 1 wafer per hour, scalable to 10 wafers per hour.
After many years of hoping that e-beam direct write technology will come to fruition, many in the industry remain skeptical of reported progress. "I'm no closer to believing that [e-beam] direct write is actually going to land," said Franklin Kalk, chief technology officer at Toppan Photomasks Inc.
Questions about nano-imprint lithography generally center around defect density. Sreenivasan said recent developments have made a lot of progress in that area.
Perhaps, regarding as the viewpoint of mass-production, the approach to improve the common DOF of the different characteristics of pattern,ex. iso- vs. dense- ,or line vs. space, is more practical and economic than that to put all resource to enhance the resolution.
The dream of e-beam direct write has been around as long as x-ray lithography, and just as successful. The e-beam problems of throughput, data management and error correction simply cannot be solved in time, or economically. EUV, or, more correctly, soft x-ray projection lithography, continues to suffer from very x-ray like problems of decades ago. The only technology with the potential to complement optical lithography is imprint, which essentially is optical lithography: it uses an I-line source, I-line resists, and quartz based photomasks. Defects are a more manageable challenge than those facing EBDW and SXPL (EUV), particularly in memory. Lithography will bifurcate into solutions for logic and solutions for memory.
E-beam is more mature than optical for sure. But electrons, primary, photo-, or secondary, are prone to random disturbance. And they go into the substrate. So the interest in DSA, though it seems sensitive to the guiding pattern size.
Truly a shame that more 'professionals' don't look more seriously at e-beam lithography themselves, and not take the word of people in the photomask industry, who would directly be threatened if mask-less lithography came into popularity. E-beam litho has demonstrated nano-level capability for more than 20 years, with comparative overlay capability equaling the best aligners out there. Yes, throughput is an issue, but at 1/6 (or less) the cost of an good immersion stepper, you can buy several!!! Truth is that even the finest nano-imprint tool or EUV stepper will require masks, and they will only be available via e-beam lithography (as well as being ridiculously expensive and short lived). Direct write is a viable technology - today!
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