Associate Professor Paul Nealey (27K JPG)

In the time it takes to read this sentence, your fingernail will have grown one nanometer. That's one-billionth of a meter and it represents the scale at which electronics must be built if the march toward miniaturization is to continue.

Reporting in the June 3 issue of the journal Science, an international team of researchers shows how control over materials on this tiny scale can be extended to create complex patterns important in the production of nano-electronics.

About two years ago, a team led by University of Wisconsin-Madison Chemical and Biological Engineering Professor Paul Nealey demonstrated a lithographic technique for creating patterns in the chemistry of polymeric materials used as templates for nanomanufacturing. They deposited a film of block copolymers on a chemically patterned surface such that the molecules arranged themselves to replicate the underlying pattern without imperfections.

That technique works well for creating templates that are neatly ordered in periodic arrays, explains Nealey, who directs the NSF-funded Nanoscale Science and Engineering Center. "But one of the challenges of nanofabrication is integrating these self-assembling materials, that naturally form periodic structures, into existing manufacturing strategies. Engineers create microelectronics under free-form design principles. Not everything fits neatly into an array. This new technique directs the assembly of blends of block copolymers and homopolymers on chemically nanopatterned substrates. The result is the creation of structures with non-regular geometries. We've now potentially harnessed the fine control over structure dimensions, afforded by self-assembling materials, to allow for the production of complex nano-electronic devices."

That kind of control is critical if computer architects are to continue advancing by Moore's Law. In 1965, Gordon Moore noted the exponential growth in the number of transistors per integrated circuit and predicted the trend would continue. It has. About every 18 months, the number of transistors in computer chips doubles. By decreasing the size of these components and, consequently, fitting more of them onto a single chip, computer speed and power improves. But before long, existing technology will run out of room.

Current manufacturing processes employing chemically amplified lithography techniques achieve dimensions as small as 50 to 70 nanometers, but that technology might not be extendable as feature dimensions shrink below 30 nanometers.

By merging the latest principles of lithography and self-assembly block-copolymer techniques, researchers at UW-Madison and the Paul Scherrer Institute in Switzerland developed a hybrid approach that maximizes the benefits and minimizes the limitations of each approach to nanomanufacturing.

"These new self-assembly materials used in conjunction with the most advanced exposure tools may enable the extension of current manufacturing practices to dimensions of 10 nanometers and less," says Chemical and Biological Engineering graduate student and co-author Mark Stoykovich.

The team includes Nealey, Stoykovich, graduate student Erik Edwards, former postdoctoral researcher Sang Ouk Kim, UW-Madison Chemical and Biological Engineering Professor Juan de Pablo, UW Physics Associate Professor Marcus Mueller, and Harun Solak of the Paul Scherrer Institute in Switzerland. The group conducted its work at the Center for NanoTechnology at UW-Madison's Synchrotron Radiation Center. It was funded in part by Semiconductor Research Corporation and the National Science Foundation's Nanoscale Science and Engineering Center.

Photolithography (shown in the left column) utilizes a number of processing steps to fabricate a topographic pattern in a photoresist material. However, traditional materials and processes will not be suitable for achieving sub-50 nm dimensions. The directed self-assembly process (shown in the right column) uses a lithographically defined template in an ultrathin imaging layer to order self-assembling materials such as block copolymers. Self-assembling materials are able to achieve smoother and more well-defined patterns at sub-50 nm dimensions than can be produced by traditional lithography. The steps required for patterning by directed assembly are similar to those already developed for photolithography; therefore, self-assembling materials may be readily inserted into current nanomanufacturing processes. (29K JPG) A, Schematic of the directed self-assembly process used to orient block copolymers. A thin film (~45 nm) of block copolymer is deposited on a patterned chemical surface and annealed such that the block copolymer phase separates into ordered domains. B, The phase segregated block copolymer forms disordered “fingerprint” features on an unpatterned surface (left image) and ordered features such as 45° and 135° bends on patterned chemical surfaces (middle and right images). (22K JPG) The directed assembly process can transform a disordered “fingerprint” pattern of block copolymer (image on left) into highly ordered stripes or bends (images on right). These well-aligned geometries are commonly utilized in the nanofabrication of integrated circuits and microelectronic devices. (28K JPG) A, Experimental results of the directed assembly of a block copolymer blend into perfect 90° bends. B, Computer simulations of block copolymer blends on chemical surface patterns show that well-defined domains are formed in both the straight and corner regions. C, The homopolymer in the blend aggregates in the corners of the bends as shown by the red spots, and facilitates the formation of these non-regular geometries. Molecular-level simulations provide a powerful tool for predicting the ability of block copolymer materials to self-assemble into complex patterns. (20K JPG) The directed assembly of block copolymer blends into perfect 90° bends is observed experimentally (image on left) and predicted by computer simulations (image on right). (33K JPG) Large arrays of bent lines can be formed with perfection by the directed self-assembly process. (47K JPG)

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Copyright 2005 The Board of Regents of the University of Wisconsin System Date last modified: Thursday, 02-Jun-2005 13:00:00 CDT Date created: 02-Jun-2005 Content By: perspective@engr.wisc.edu Thank you for visiting!