Nanotechnologies for Nanoparticles and Wires

Yang-Kyu Choi1 and Ji Zhu
(Professor Jeffrey Bokor)

The fabrication of nanoscale patterns below 10 nm has been a goal of many researchers for potential applications such as sensors, soft X-ray optical device components, electronic circuit elements, or catalysts. Electron beam lithography is the most commonly used technique for nanometer pattern generation. However, the generation of secondary electrons during electron bombardment makes it difficult to achieve sub-10 nm patterning. Electron beam lithography is also a sequential pattern producing technique and is very time-consuming compared to photolithography-based processes that produce the whole pattern at once using a mask. This is also the case for other scanning probe based lithography techniques. In this work two sub-lithographic patterning technologies, spacer lithography and nanosphere lithography, will be studied. Spacer lithography using a sacrificial layer and a chemical vapor deposition (CVD) spacer layer was demonstrated [1,2]. Sacrificial layers (to support the spacers) were initially defined by conventional lithography and plasma etching. Then, another thin CVD layer that would be spacers was deposited and etched back. After removal of sacrificial structures, these spacers were transferred to a substrate with anisotropic plasma etch. Thus, minimum-sized features were defined not by photoresist but by sidewall spacers deposited by CVD. One of the benefits in the spacer lithography is that it doubles the pattern density achievable by lithography. If this spacer lithography is used n times in succession, 2n lines can generated from a single lithographically defined line. With nanoimprint technology, Pt nanowires and Pt nanoparticles can be fabricated by the spacer lithogrpahy for catalysts and nanowires composed of other materials can be used for chemical and biosensors. Nanopshere lithography uses a monolayer of nanobeads, which are coated by a spinning process [3]. Well-ordered nanogaps can be formed by these adjacent nanobeads. Combining the nanosphere lithography with a metal lift-off process, nanosize metal particles can be patterned, which can be used as catalysts for carbon nanotube growth and as an etch stopper to make nanopillars. The packed nanobeads can also be served as an etch stopper to make nanoholes.

[1]
Y.-K. Choi, T.-J. King, and C. Hu, "A Spacer Patterning Technology for Nanoscale CMOS," IEEE Trans. Electron Devices, 2002.
[2]
Y.-K. Choi, T.-J. King, and C. Hu, "Spacer FinFET: Nanoscale Double-Gate CMOS Technology for the Terabit Era," Solid-State Electronics, Vol. 46, 2002.
[3]
J. C. Hulteen, D. A. Treichel, M. T. Smith, M. L. Duval, T. R. Jensen, and R. P. Van Duyne, "Nanosphere Lithography: Size-Tunable Silver Nanoparticles and Surface Cluster Arrays," J. Physical Chemistry B, Vol. 103, 1999.
1Postdoctoral Researcher

Send mail to the author : (ykchoi@eecs.berkeley.edu)


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