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Harry Levinson: Lithography roadmap faces difficult challenges

Posted on: 26-Feb-2007

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Setting the stage for the SPIE Advanced Lithography event which starts in San Jose today (Feb. 26), AMD’s Harry Levinson said the lithography roadmap beyond the 50-nm half-pitch presents unprecedented challenges.
“Things are going to be very different, in ways that maybe we don’t understand yet. The lithography roadmap used to have more clarity, but now it is not easy for any of us to see that far down the road,” Levinson said at an all-day “LithoVision” event Sunday organized by Nikon Precision.
The extreme ultraviolet (EUV) scanners still face “a very long distance from the lab to the factory floor,” he said. Semiconductor manufacturers need EUV lithography in the 2012 time frame for 36-nm half-pitch designs. At the very latest, chip companies need to develop pilot lines by 2010 to test out EUV scanners, processing several hundred wafers per day. “Until we do it over and over again, with 200 to 300 wafers per day with reticle handling, we can’t understand the production challenges,” said Levinson, who has been a key figure in the lithography roadmap of the International Technology Roadmap for Semiconductors.
The EUV systems developed for pilot lines must have throughputs of 10 wafers per hour. Also, the EUV resists must be capable of sensitivities of 20 milliJoules  “at the bare minimum."
The designs must be compatible with immersion scanners, he added, implying that 193-nm immersion scanners with double patterning could serve as a backup to the EUV systems in some cases.
However, double patterning presents “severe” design rule restrictions. Designs have vertical and horizontal lines. To double pattern in both directions would involve four exposures, which Levinson said “is not cost effective.”
The lithography research community continues to consider high-index immersion lithography, but finding a bottom lens element is proving difficult. Nikon executives said 2007 will be a key decision year for the high-index research program. The lens materials now being considered suffer from intrinsic birefringence and thermal aberration problems. In order to achieve commercial success, a high-index immersion tool would need to be ready by 2011, a difficult target, they said.
Toshikawu Umatate, a Nikon general manager, said Nikon will soon introduce its S610C immersion scanner, with a numerical aperture of 1.3, capable of 43-nm lines and spaces. That system is now in “the performance tuning phase” at beta customers.
“This year is the real ramping up year for water-based immersion,” Umatate said, with scanner makers now unable to meet demand for the wet tools.
He said the company is moving “full speed ahead” on systems optimized for double patterning with immersion scanners. The S61X systems would be optimized for higher throughput and enhanced overlay, he said.
Also, Nikon will introduce its first EUV development tool, the EUV1, later this year, he said. The company will finalize its plans for the EUV2 system this year.

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