原创 EUV lithography still a work in progress

As has been the case for the past several years, apprehension over the development of extreme ultraviolet (EUV) lithography was one of the oft-repeated themes at this year's Semicon West fab tool tradeshow in San Francisco, United States.

"EUV is the highest priority for our industry," said Luc Van den Hove, president and CEO of European microelectronics research institute Imec, in a panel discussion at the event.
In May, Dutch lithography vendor ASML finalized a deal to acquire lithography source vendor Cymer for about $2.6 billion. The deal is largely considered an attempt by ASML to take a firmer hand in the development of an EUV source. Cymer is one of three developers trying to create a source that would be powerful enough to support commercial production throughput of an EUV lithography tool.

In February, at the SPIE Advanced Lithography Conference, ASML showed data indicating that it had raised the maximum power on its power source to 55 watts. Ryan Young, a spokesman for ASML, said this week that 55 watts would be enough to support EUV tool throughput of about 43 wafers per hour.

More significant, according to Young, is that ASML has shown the power source can support a maximum power of 50 watts for long periods of time.

Young also noted that the development work is being done on ASML's pre-production EUV machine, the NXE:3100. When ASML transfers the source to its NXE:3300 EUV tool, which has a larger drive laser, the 50 watts will become 80 watts, enough to support throughput of more than 60 wafers per hour.

Young added that improving source power—while the most significant stumbling block to putting EUV in production—is only one place where ASML needs to make progress. ASML will continue working on improving the raw power of the source, but also focus on other needed improvements in the power source around availability and dose control.

ASML's latest goal is to be able to support a throughput of about 70 wafers per hour sometime in 2014. According to Young, that's roughly the throughput threshold that most customers say would make it worthwhile to adopt EUV. "But every customer's process is different," he added.

Chipmakers would ideally prefer EUV tools with a throughput of 100 to 150 wafers per hour to make production cost effective. Some say a tool throughput of 60 to 80 wafers per hour would be a sufficient starting point.

The original plan was for EUV to be in production years ago, but development hiccups have pushed out the technology multiple times. ASML has six pre-production EUV development tools currently in the field.

Intel—which last year acquired a 15 per cent stake in ASML and ponied up additional funds specifically for the development of EUV in a deal worth a total of $4.1 billion—has been hoping to deploy EUV lithography at the 10 nm node in the second half of 2015. Intel also said it would be prepared to extend optical immersion lithography to that node in the event that EUV is not ready. Samsung and TSMC have entered into similar deals with ASML.

Ludo Deferm, executive vice president of business development at Imec, said this week that extending optical immersion to that node may not be economically feasible. Because extending optical immersion to 10 nm could require three or more exposures—and thus three or more photomasks for critical layers—the costs involved would increase exponentially.

But Deferm told us Imec is confident that EUV will eventually be put in production. "We are confident that it will come," he said. "I don't have a crystal ball, either. We can't predict the future."

Dylan McGrath
EE Times