Argonne National Laboratory Center for Nanoscale Materials U.S. Department of Energy

A Better Etching Technique Is Invented

Mark Holt (Argonne Center for Nanoscale Materials) examines a sample in the Hard X-Ray Nanoprobe

Deep canyons can be etched into materials at the nanoscale with a new SIS-based lithography technique

Nanoscientists at Argonne's Center for Nanoscale Materials and Energy Systems Division have discovered a new way to transfer patterns onto different materials, an innovation that combines new tricks with an old technology. One of the biggest recent questions facing materials science has involved the development of better techniques for high-resolution lithographies such as electron-beam (e-beam) lithography. E-beam lithography is used to manufacture the tiniest of structures, including microelectronics and advanced sensors; beams of electrons are part of a process that "prints" desired patterns into the substance. Transferring patterns more deeply into materials would allow scientists to craft better electronics.

To create a pattern by using e-beam lithography, researchers expose a pattern within a polymer film called a “resist” that modifies its solubility to a developer solution. Once developed, the remaining resist on the substrate acts as a protective layer against chemical etch, in particular plasma etch, that will remove unprotected areas of the substrate. Because resists have limited etch resistance, an intermediate “hard mask" typically is laid between the resist and the substrate. Ideally, the hard mask remains on the substrate long enough for the desired features to be etched and then is cleanly removed. Unfortunately, the extra layer often results in rough edges, additional cost, and other processing complications.

The new alternative technique is called sequential infiltration synthesis (SIS) and involves the controlled growth of inorganic materials within polymer films. CNM researchers have demonstrated that this process increases the etch resistance of, for example, polymethylmethacrylate resist by 37-fold and of another resist known as "ZEP-520" by more than 5-fold. These resists are among the highest resolution resists currently on the market. By increasing the etch resistance of these materials, higher resolution structures can be achieved, enabling novel applications in areas such as plasmonics, nanofluidics, single-electron transistors, and X-ray optics.

By combining SIS with block copolymers, molecules that can assemble themselves into a variety of tunable nanostructures, this technique can be extended further to create even smaller features than are possible by using e-beam lithography.

Y-C Tseng, Q. Peng, L.E. Ocola, D.A. Czaplewski, J.W. Elam, and S.B. Darling, J. Mater. Chem., 21, 11722-11725, 2011 (online)

Y-C Tseng, Q .Peng, L.E. Ocola, J.W. Elam, and S.B. Darling, J. Phys. Chem. C, DOI: 10.1021/jp205532e, July 11, 2001 (online)

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August 2011

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