Mechanistic Study of the Nanoscale Negative-Tone Pattern Transfer from DNA Nanostructures to SiO₂

Abstract

We report a mechanistic study of a DNA-mediated vapor phase HF etching of SiO 2 . The kinetics of SiO 2 etching was studied as a function of the reaction temperature, time, and partial pressures of H 2 O, HF, and 2-propanol. Our results show that DNA locally increases the etching rate of SiO 2 by promoting the adsorption of water and that the enhancement effect mostly originates from the organic components of DNA. On the basis of the mechanistic studies, we identified conditions for high-contrast (>10 nm deep), high-resolution (∼10 nm) pattern transfers to SiO 2 from DNA nanostructures as well as individual double-stranded DNA. These SiO 2 patterns were used as a hard mask for plasma etching of Si to produce even higher-contrast patterns that are comparable to those obtained by electron-beam lithography. ■ INTRODUCTIONIn recent years, research in DNA nanostructures has developed to a stage in which arbitrarily shaped and mechanically robust nanostructure can be constructed 1−8 with a theoretical precision of <5 nm at a cost as low as $6/m 2 . 9 The deposition of DNA nanostructures on the substrates has been demonstrated with precise control over their location and orientation, making them ideal templates for high-resolution, low-cost nanofabrication. 10−12 However, the pattern transfer from DNA nanostructures to inorganic substrates remains a bottleneck of this area of research. Tremendous efforts were dedicated to overcome the lack of chemical stability of DNA and the inadequate adhesion interaction between DNA and the substrate. 13 Metallization is the most widely used approach to DNAbased nanofabrication. Solution phase metallization of λ-DNA was first demonstrated by Sivan and co-workers. 14 Recently, the metallization of different metals, such as Ag, Cu, Ni, and Au, on DNA strands and DNA nanostructures has been demonstrated. 2,15−17 In addition to the deposition of metal onto the whole nanostructure, site-specific metallization was also made possible by modifying DNA nanostructure with binding sites that accept DNA-modified Au or Ag nanoparticles. 18−20 In addition to these solution phases approaches, vapor phase deposition of metals onto DNA has also been reported by the groups of Mao and Woolley. They used DNA to pattern vapor phase deposited metal, and the resulting metal film can be used as a hard mask for patterning the underlying substrate. 21−23 Our group recently showed that DNA nanostructures can modulate certain surface reactions to produce a faithful pattern transfer from the DNA nanostructures to an inorganic substrate. 24,25 In one of the studies, DNA was shown to have a local effect on the vapor phase HF etching, which resulted in direct negative-tone and positive-tone pattern transfers from DNA to SiO 2 . 24 The fact that DNA can be used to directly pattern SiO 2 carries significant technological significance because SiO 2 is one of the most important hard mask materials for semiconductor nanofabrication. 26 Although our early study established vapor phase HF etching as a promising appr...

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