Advanced lithography for nanofabrication Page: 3 of 8
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ADVANCED LITHOGRAPHY FOR NANOFABRICATION
Frank Hui and Gyula Eres
Oak Ridge National Laboratory, P.O. Box 2008
Solid State Division, Bldg. 31 50, MS 6056, Oak Ridge, TN 37831-6056
ABSTRACT
A novel method for generating lateral features by patterning the naturally forming surface
hydride layer on Si is described. Because of the relatively strong chemical bonding between
silicon and hydrogen, the hydride layer acts as a robust passivation layer with essentially zero
surface mobility at ordinary temperatures. A focused electron beam from a scanning electron
microscope was used for patterning. Upon losing the hydrogen passivation the silicon surface
sites become highly reactive. Ideally, the lifetime of such a pattern in a clean environment should
be infinite. Deliberate exposure of the entire wafer to a suitable gas phase precursor results in
selective area film growth on the depassivated pattern. Linewidths and feature sizes of silicon
dioxide on silicon below 100nm were achieved upon exposure to air. The silicon dioxide is robust
and allows effective pattern transfer by anisotropic wet-chemical etching. In this paper, the
mechanism of hydrogen desorption and subsequent pattern formation, and the factors that govern
the ultimate pattern resolution will be discussed.
INTRODUCTION
Electron beam lithography (EBL), X-ray, ion beam, and focused ion-beam (FIB) lithography
are some of the candidates for the next generation microfabrication processes (sub 100nm feature
size) beyond optical lithography. However, none of the above processes satisfy the requirements
for both high yield and high resolution. EBL and FIB have high ultimate resolution but suffer from
slow speed, while the other methods support high yield processes but provide limited resolution.
In terms of high resolution, STM lithography is capable to produce the smallest structures.
Linewidths down to I nm have been demonstrated on hydrogen passivated silicon surfaces [1].
However, because of the extremely slow writing speed and the narrow field of view, it is unlikely
that STM patterning will become useful for high volume device fabrication. In addition, the STM
fabricated ultrahigh resolution patterns were found to be too frail to survive the subsequent pattern
transfer steps [2]. EBL is attractive for novel patterning methods because other than STM, it
provides the highest resolution among all patterning tools and has a well established track record in
device fabrication for research purposes [3].
In this paper, we report results concerning a novel resistless e-beam lithography process that
involves electron beam induced patterning without the use of organic polymer resist such as
PMMA. The patterning medium is the surface hydride layer on silicon. The function of the
electron beam is to chemically alter the passivated surface of the substrate. The exposed patterns
are'transferred by subsequent processing. In this work, we employed anisotropic wet chemical
etching of the substrate. The advantages of resistless EBL are total elimination of all the toxic
chemicals associated with the resist processes and a higher ultimate resolution resulting from the
absence of line broadening by electron scattering processes in the resist. In this report we describe
the linewidth dependence on the electron beam energy, the electron exposure dose, and the
substrate thickness.
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Hui, F. & Eres, G. Advanced lithography for nanofabrication, article, June 1, 1997; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc711460/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.