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Directed self-assembly gains steam

Posted: 07 Mar 2011 ?? ?Print Version ?Bookmark and Share

Keywords:DSA? defect density? EUV?

Semiconductor manufacturing has found a viable alternative technology. Directed self-assembly (DSA) is a process based on an idea that was kept hidden inside research labs until recently.

"Directed self-assembly cannot be ignored," said Christopher Bencher, member of the technical staff at Applied Materials Inc., at the SPIE Advanced Lithography conference. Bencher further suggested that DSA should be moved from the list of emerging lithography technologies to the "current" technologies list.

At SPIE, Bencher presented data on self-assembly patterning for cells with a half-pitch of less than 15nm that was collected through a joint project with IBM Research. Bencher noted that while lithographers have been enthusiastic about DSA, the biggest concern has been defect density. Bencher said his project demonstrated the use of DSA to build 12nm line/space structures across an entire 300mm wafer with a very low rate of less than 1 percent of "dislocation" defects.

Hundreds of particle defects were also measured during the project, but, according to Bencher, particle defects introduced through the use of DSA are no different than particle defects encountered during the use of any new process technology material, and will be reduced through better filtration in the fab. Bencher's project was concerned mainly with dislocation defects because, he said, this is a new type of defect inherent to DSA.

"This clearly puts us on a trajectory to make DSA feasible, with fairly good defect control," Bencher said.

In DSA, a block copolymer or polymer blend is deposited on a substrate, usually by spin coating, and subjected to an annealing process that "directs" it to form ordered structures. Researchers say DSA is compatible with conventional 193nm lithography equipment and would eliminate the need for dual exposure steps.

DSA first landed on the International Technology Roadmap for Semiconductors (ITRS) as a potential solution for leading-edge, critical layer lithography in 2007 and remained part of 2009 ITRS. The technology is also considered complementary to next-generation lithography candidates such as extreme ultraviolet (EUV) lithography and nano-imprint lithography.

But even the most enthusiastic supporters of DSA acknowledge that the technology is years away from being used in CMOS production, even in a best-case scenario. Defect density is only one of a number of technical hurdles DSA must overcome to be viable in volume production.

Yoshi Hishiro, director of R&D at materials supplier JSR Micro Inc., estimated that DSA was at least two to three years away from being used in niche CMOS production.


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