Chips that put themselves together ........

Nano Patterning
IBM brings closer to reality chips that put themselves together

By Gary Stix

OLD AND NEW: Conventional lithography exposes a photoresist to ultraviolet light. An etchant then removes the exposed part of the photoresist. Self-assembly patterning occurs when a diblock copolymer is heated, thereby separating the two polymers in the material into defined areas before the PMMA is etched away. The template of cyclindrical holes is transferred into the silicon dioxide before the holes are filled with nanocrystalline silicon used to store data (steps not shown).
Self-assembly has become a critical implement in the toolbox of nanotechnologists. Scientists and engineers who explore the nano realm posit that the same types of forces that construct a snowflake--the natural attractions and repulsions that prompt molecules to form intricate patterns--can build useful structures--say, medical implants or components in electronic chips. So far much of the work related to self-assembling nanostructures has been nothing more than demonstrations in university laboratories. To go beyond being a scientific curiosity, these nanotech materials and techniques will have to get from benchtop to a $2-billion semiconductor fabrication facility.
Four years ago two members of the technical staff at the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., began to contemplate how they might transform the vision of self-assembly into a practical reality. The collaborators, Charles Black and Kathryn Guarini, knew that the grand academic ambitions of making an entire set of chip circuits from self-assembly had to be set aside. Instead the best way to begin, they thought, might be to replace a single manufacturing step. "The idea was that if we could ease the burden in any of the hundreds of steps to make a chip, we should take advantage of that," Black says.

They first had to select what type of molecules might self-construct without disrupting routine silicon manufacturing practices. Polymers were an obvious choice. They make up the "resist" used in photolithography--the material that, once exposed to ultraviolet or shorter-wavelength light, is washed away to form a circuit pattern. During the first two years of their quest, the duo spent time learning about polymers and the optimal temperatures and thicknesses at which they would self-assemble. They built on the work of Craig J. Hawker of the IBM Almaden Research Center in San Jose, Calif., and that of former IBMer Thomas P. Russell, a polymer scientist at the University of Massachusetts at Amherst. Both had done research on how polymers self-assemble on silicon. With this knowledge


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