Materials Science

Advantages of Neutrality

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Science  18 Aug 2006:
Vol. 313, Issue 5789, pp. 893
DOI: 10.1126/science.313.5789.893b

Electron beam lithography, often used to pattern the smallest features on semiconducting silicon substrates, can also modify insulating substrates. However, at typical beam energies, the insulating surface builds up negative charge that deflects the beam and so distorts the desired pattern. Several approaches have been developed to overcome this problem, but they require additional sample processing steps or complex gas-handling and vacuum equipment. Joo et al. note that at lower energies, electron beams can instead induce positive charging of insulating surfaces; therefore, a critical energy exists for which the surface will remain neutral. For 65-nm-thick poly(methyl methacrylate) films on glass, they determine a critical energy value of 1.3 keV. By tuning the incident beam to this energy, they successfully create features finer than 100 nm on this substrate. A 5-keV beam, in contrast, produces distortions that are clearly evident in scanning electron micrographs. — PDS

Nano Lett. 6, 10.1021/nl061211q (2006).

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