News in Brief Lithography // New Stamping Process to Pattern Biomolecules © Based on Material by UCLA, USA
Researchers at UCLA (US) have turned the conventional “soft lithography” process on its head: Instead of using a stamp to transfer molecules onto bare surfaces, they have used chemically treated stamps to remove molecules already in place on gold substrates, essentially peeling away select molecules through chemical bonds to create precise patterns measuring just a few molecules across. The new process, called Chemical Lift-off Lithography (CLL), results in higher-resolution patterning and avoids the blurring problems of earlier techniques. The stamp used in the new process is molded by using a “master” made with more sophisticated and expensive tools than those used in making rubber stamps for offices and children, but the stamps can be used over and over again. Between each use, they are simply reactivated by an oxygen plasma.
The chemical bonds formed at the stamp-substrate interface are sufficiently strong to remove not only molecules in the monolayers but also one layer of gold atoms from the substrate. This observation settled a long-running discussion over whether, for such monolayers, gold-gold bonds break more easily than molecule-gold bonds – they do, the researchers found. The research team was able to fabricate a variety of high-resolution patterned features, and stamps were cleaned and reused many times with little feature deterioration. The remaining monolayer, they found, can act as a resist for etching exposed gold features. The backfilling of new molecules into the lifted-off areas enabled patterned protein capture, and sharp 40nm chemical patterns were achieved.
Wei-Ssu Liao, Sarawut Cheunkar, Huan H. Cao, Heidi R. Bednar, Paul S. Weiss, and Anne M. Andrews: Subtractive Patterning via Chemical Lift-Off Lithography, In: Science, Vol. 337, No. 6101, September 21, 2012, Pages 1517- 1521, DOI: 10.1126/science.1221774: http://dx.doi.org/10.1126/science.1221774