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Nanolitho effort harnesses self-assembly

Posted: 08 Aug 2003 ?? ?Print Version ?Bookmark and Share

Keywords:nanoscale? silicon substrate? nanoscale chip?

Nanoscale patterning of silicon substrates with regular, repeatable, atomically perfect application-specific templates could enable manufacturable nanoscale chips within the decade, according to scientists at the University of Wisconsin's Materials Research Science and Engineering Center.

The work "has the potential to become an inexpensive and routine step for semiconductor manufacturers," said team leader Paul Nealey. "Now we hope that semiconductor manufacturers will adopt our techniques to build real nanoscale chips."

Despite breakthroughs in nanoscale components, from single-electron transistors to quantum dots, techniques for casting them into chips are still uncertain. The Achilles' heel, the Wisconsin group says, is irregularity.

The lab, one of the National Science Foundation's 27 Research Science and Engineering Centers (MRSECs), aimed to show that curing the irregularity would lead to manufacturability. "We have shown that our technique can achieve dimensions of tens of nanometers," said Nealey, whose work was done in cooperation with the Semiconductor Research Corp., a consortium that includes AMD, IBM, Intel and Motorola.

"In storage alone, our work could someday result in a computer with 4,000 Gbytes of memory," said Wisconsin-MRSEC director Juan de Pablo.

The team used block co-polymers that "self-assemble like snowflakes," according to their report, enabling nanoscale patterns to form only in designated areas on a chip. In effect, the technique applies a nanoscale mask to the substrate in a manner similar to conventional lithography.

Future silicon substrates could not only host arrays of identical molecular-size components, but could also take advantage of conducting polymers to someday interconnect those components with nanoscale wiring. "All that we've done in this study is to create a pattern, show that the polymer follows the pattern and show that the final result is completely free of defects, which is very hard to do at these small sizes," said Nealey.

Block co-polymers are matching pairs of compounds with two or more long polymer chains linked at the ends. Normally they would self-assemble into useless clumps, rings, cylinders or broad spirals. By chemically altering the surface of a conventional silicon wafer, the researchers were able to use extreme-ultraviolet light to lay down straight, parallel lines of alternating chemicals as close as 20nm apart.

By washing with a solution of the block co-polymer (two polymers, one attracted to one kind of line and the other to the alternate type of line), the team was able to mask out parallel lines. "Our technique delivers registration and overlay - two critical requirements that have been missing from other attempts at nanoscale lithography," said Nealey. "This kind of hybrid technology can integrate self-assembling materials, such as block co-polymers, into existing manufacturing processes, such as lithography, and deliver molecular-level control."

The group next hopes to crisscross lines to create nanoscale domains for ultradense memory arrays of, for instance, quantum dots.

- R. Colin Johnson

EE Times

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