Direct-write Electron Beam Lithography: History and State of the Art
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Abstract Direct-write electron beam lithography is a patterning technique that has rapidly evolved over the last 40 years. For many years it has been possible to use electrons to pattern lines with widths as narrow as 10 rum. Recent advances in resist materials, electron sources, and system integration have further enhanced the capabilities. High-sensitivity resists provide substantial increases in the throughput without sacrificing resolution. Thermal field-emission sources improve the stability and reduce the minimum attainable spot size. Modem lithography systems integrate the electron beam column with advanced control electronics, making a system capable of nanometer-scale placement accuracy. In addition to these improvements, the technology is more accessible now than ever before, thanks to the proliferation of lithography systems consisting of modified scanning electron microscopes.
Introduction and Historical Perspective Scanning electron beam lithography uses a finely focussed beam of electrons to make changes in the surface of a material. The beam is scanned across the surface and sequentially writes a desired pattern in the surface. The term "direct-write" refers to the use of this technique for the direct patterning of devices, as opposed to mask writing. This patterning technique is capable of writing lines with widths as narrow as a few nanometers. This paper discusses some of the major historical developments of this technology, and also highlights the capabilities of modem lithography systems. In 1959, Richard Feynman gave his famous address to the American Physical Society entitled "There's Plenty of Room at the Bottom"'. In this talk, he proposed a number of challenges to the scientific community in the area of miniaturization. These propositions proved to be visionary, and made remarkably accurate predictions regarding many aspects of nanofabrication. Among these was the use of scanning cathode rays for the deposition of materials Why can not we write the entire 24 volumes of the Encyclopedia Britannicaon the head of a pin? ... How do we write small?... We can reverse the lenses of the electron microscope in order to demagnify as well as magnify... We could write with that spot like we write in a TV cathode ray oscilloscope, ... andhaving an adjustment which determines the amount of material which is going to be deposited Feymnan already realized that the direct modification of metal by scanning beams would be inefficient so he proposed a yet undiscovered electron beam resist: If it doesn't work for a metal surface, it must be possible to find some material with which to coat the originalpin so that, where the electrons bombard, a change is made which could be recognized later.
33 Mat. Res. Soc. Symp. Proc. Vol. 584 © 2000 Materials Research Society
These ideas were prophetic, considering that they were made during the early, formative years of the scanning electron microscope. However, it would not be long before research along these lines demonstrated the capabilities of electron beams as pa
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