Editing Electron-beam lithography (section)

==New frontiers==
To get around the secondary electron generation, it will be imperative to use low-energy electrons as the primary radiation to expose resist. Ideally, these electrons should have energies on the order of not much more than several [[electronvolt|eV]] in order to expose the resist without generating any secondary electrons, since they will not have sufficient excess energy. Such exposure has been demonstrated using a [[scanning tunneling microscope]] as the electron beam source.<ref name="marrian">{{cite journal|title=Electron-beam lithography with the scanning tunneling microscope|first=C.R.K. |last=Marrian|journal=Journal of Vacuum Science and Technology|issue=B|volume=10|year=1992|pages=2877–81|doi=10.1116/1.585978|bibcode = 1992JVSTB..10.2877M |url=https://zenodo.org/record/1236102}}</ref> The data suggest that electrons with energies as low as 12&nbsp;eV can penetrate 50&nbsp;nm thick polymer resist. The drawback to using low energy electrons is that it is hard to prevent spreading of the electron beam in the resist.<ref name="mayer">{{cite journal|title=Field emission characteristics of the scanning tunneling microscope for nanolithography|first=T.M. |last=Mayer|journal=Journal of Vacuum Science and Technology|issue=B|volume=14|year=1996|pages=2438–44|doi=10.1116/1.588751|bibcode = 1996JVSTB..14.2438M|display-authors=1|author2=<Please add first missing authors to populate metadata.> |url=https://zenodo.org/record/1236104}}</ref> Low energy electron optical systems are also hard to design for high resolution.<ref name="hordon">{{cite journal|title=Limits of low-energy electron optics|first=L.S. |last=Hordon|journal=Journal of Vacuum Science and Technology|issue=B|volume=11|year=1993|pages=2299–2303|doi=10.1116/1.586894|bibcode = 1993JVSTB..11.2299H|display-authors=1|author2=<Please add first missing authors to populate metadata.> }}</ref> Coulomb inter-electron repulsion always becomes more severe for lower electron energy.

[[Image:PMMA Linewidth vs SPL Dose.PNG|right|thumb|300 px| '''Scanning probe lithography.''' A scanning probe can be used for low-energy electron beam lithography, offering sub-100&nbsp;nm resolution, determined by the dose of low-energy electrons.]]

Another alternative in electron-beam lithography is to use extremely high electron energies (at least 100&nbsp;keV) to essentially "drill" or sputter the material. This phenomenon has been observed frequently in [[transmission electron microscopy]].<ref name="egerton">{{cite journal|title=Radiation damage in the TEM and SEM|author=Egerton, R. F.|journal=Micron|volume=35|year=2004|pages=399–409|doi=10.1016/j.micron.2004.02.003|pmid=15120123|issue=6|display-authors=etal}}</ref> However, this is a very inefficient process, due to the inefficient transfer of momentum from the electron beam to the material. As a result, it is a slow process, requiring much longer exposure times than conventional electron beam lithography. Also high energy beams always bring up the concern of substrate damage.

[[Interference lithography]] using electron beams is another possible path for patterning arrays with nanometer-scale periods. A key advantage of using electrons over photons in [[interferometry]] is the much shorter wavelength for the same energy.

Despite the various intricacies and subtleties of electron beam lithography at different energies, it remains the most practical way to concentrate the most energy into the smallest area.

There has been significant interest in the development of multiple electron beam approaches to lithography in order to increase throughput. This work has been supported by [[SEMATECH]] and start-up companies such as [[Multibeam Corporation]],<ref>[http://www.multibeamcorp.com Multibeam Corporation]. Multibeamcorp.com (2011-03-04). Retrieved on 2011-08-27.</ref> Mapper<ref>[http://www.mapperlithography.com Mapper Lithography] {{Webarchive|url=https://web.archive.org/web/20161220140103/http://www.mapperlithography.com/ |date=2016-12-20 }}. Mapper Lithography (2010-01-18). Retrieved on 2011-08-27.</ref> and IMS.<ref>[http://www.ims.co.at IMS Nanofabrications]. IMS Nanofabrication(2011-12-07). Retrieved on 2019-02-28.</ref> IMS Nanofabrication has commercialized the multibeam-maskwriter and started a rollout in 2016.<ref>[https://www.ims.co.at/products/ IMS Nanofabrications]. IMS Nanofabrication(2011-12-07). Retrieved on 2019-02-28.</ref>