Aaron Hand

Maskless E-Beam: Worth Another Look?
June 5, 2008

It’s interesting to hear the same person who made such a push for immersion now making a similar case for electron-beam direct-write (EBDW) lithography. Given his success with immersion, not to mention his considerable experience in the industry, it’s hard not to listen to what TSMC’s Burn Lin now has to say about maskless technologies, especially when he says himself that he has been an “optical bigot” most of his life.

And he makes some awfully good arguments: the ability to cluster tools to give a chipmaker just the amount of throughput it needs or can afford; a much smaller footprint than EUV; and the clincher: cost. There’s the potential for a multiple e-beam tool to have about the same cost as an immersion scanner, Lin contends, both in terms of cost of ownership (CoO) and wall power (bunking initial conceptions that e-beam would be a power-hungry solution). To make his cost argument, Lin presented a chart comparing various lithography possibilities.

To compare these costs, Lin detailed some assumptions: Water immersion tools will cost 40 million euros ($62.58M), with ¥800 million ($7.64M) for the track; and EUV tools will cost 50 million euros ($78.23M), plus ¥700 million ($6.69M) for a 100 wph track, and ¥300 million ($2.87M) for a 20 wph track. The final column shows what a 20 wph e-beam system would have to cost in order to compete with each technology. The $3.75M cost is unrealistic, so does not stand a chance against single-exposure water immersion. But competition with double-patterning water immersion and 100 wph EUV is feasible, and with 20 wph EUV is easy.

Maskless lithography has been talked about for years, in a variety of forms. Its leading downfall has been throughput, but research has continued relatively quietly nonetheless because it offers some real resolution advantages, particularly for contact layers. In fact, one of the most critical factors affecting maskless adoption at this point, according to Lin, is that it has been around too long, and people have already formed their conceptions. “One has to change their concepts and look at the potential of a multiple e-beam system,” he said. This is not the old e-beam, he added later. “This is a new era for e-beam.”

Besides Lin’s presentation, several other promising presentations were made at the Litho Forum updating attendees on maskless e-beam progress, including talks from Mapper Lithography (Delft, Netherlands), Multibeam Systems (Santa Clara, Calif.), IMS Nanofabrication (Vienna, Austria) and CEA-Leti (Grenoble, France). (By the way, Mapper shows a great movie showcasing its technology.)

During the panel discussion that wrapped up the Litho Forum talks, Freescale’s Will Conley added, “I very much support Burn and the maskless team. I think in the low-power device community, this kind of a solution is quite nice. And we, along with similar companies to Freescale, we have a lot of products that are very low runners, and we may build 50 wafers per mask set, or maybe 100 wafers per mask set, or something like that. And it’s expensive for us to do it, but it’s part of our business model, and we do make money. And if this kind of technology exists for us, it’s possible it could even expand that kind of a business, and provide more revenue for us in that area. So there’s a lot of companies I think that can benefit from it.”

However, when Conley posed a question — “Would those companies participate in funding it?” — he got no immediate reply, and the topic moved on. But he did get a response, perhaps, in the form of Litho Forum survey results. In the survey conducted at the close of the two-day conference, one open-ended question attendees were asked was which alternative technologies should be pursued more aggressively to achieve ITRS goals. The clear winner was maskless, with runners up including nanoimprint, interference, 3-D integration and directed self-assembly.

Couched another way, when attendees were asked which technologies warrant reconsideration, based on information presented at the Litho Forum, 21% of the respondents said that maskless was one to reconsider. The only technology ranking higher was EUV, with 29%.

You can view the full results of the Litho Forum surveys in a 20-minute webcast produced by Semiconductor International and presented by Litho Forum program chair Bernie Roman.

One company making news recently for its use of e-beam direct write (EBDW) technology is e-Shuttle Inc. (Kawasaki, Japan), a joint venture started up by Fujitsu Ltd. and Advantest Corp. to provide prototyping services for leading-edge ICs. E-Shuttle is now delivering 65 nm logic ICs manufactured with the maskless technology, lauded as the first full-scale application of EBDW.

Presenting last week at EIPBN (International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication) in Portland, Ore., Shinji Sugatani, e-Shuttle’s general manager, showed the available markets for maskless lithography, provided a given throughput. Although at 0.5 wph it’s difficult to define a market beyond R&D applications, a throughput of 0.5-3 wph enables LSI prototyping with a market size for EBDW tools of ~¥10 billion ($94.32M), and throughput of 3-30 wph enables small-volume or mid-size production of ASICs and/or MOS logic, for example, with a tool market size of ¥30-200 billion ($282.94M-$1.89B). If, with a multi-column system, throughput could reach 30-100 wph, Sugatani could foresee maskless technology unseating EUV at mass production levels, reaching a tool market size of ¥1 trillion ($9.44B). That is not the level of production e-Shuttle aims to achieve, however, since mass production is handled by parent company Fujitsu.

So, suffice it to say that throughput is a major consideration in improving the chances for maskless e-beam, and it will require innovation, Sugatani said. As Chris Mack quipped during the Q&A after Lin’s presentation, maskless is the only technology that makes EUV throughput seem high. According to Lin, though, clustering multiple e-beam tools together looks like a good bet.

Posted by Aaron Hand on June 5, 2008 | Comments (5)