Faster with fluorine

Etch-resistant nanoscale features can be patterned on a surface at high speeds using an atomic force microscope tip immersed in a fluorocarbon solvent

Credit: © 2007 Wiley

The tip of a scanning probe microscope can be used to pattern nanosized features on surfaces in a variety of different ways. For example, simple physical contact can be used to scratch a substrate or, alternatively, a chemical substance can be transferred to selected areas of a surface from the probe tip. Another method relies on the localized decomposition of an organic solvent — and deposition of the resulting material — when an electric field is generated between the tip and a substrate immersed in such a medium.

With this latter approach, Jean Fréchet and co-workers¹ at the University of California, Berkeley and Lawrence Berkeley National Laboratory in the USA have now patterned sub-50-nm features onto silicon substrates at speeds of up to centimetres per second. An atomic force microscope tip is traced above a silicon surface immersed in a fluorocarbon solvent (perfluorooctane). A large electric field (approximately 10⁹ V m^-1) generated between the tip and substrate causes the solvent to decompose into highly reactive fragments that crosslink with one another to form deposits of an amorphous film comprising carbon and fluorine.

The deposited material is resistant to dry etchants such as SF₆ plasma, which could be used to transfer the patterns into the underlying silicon substrate. Significantly, this lithographic process can pattern areas much faster than electron-beam lithography, or even similar methods that use non-fluorinated solvents.