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Jongyoon Han and H. G. Craighead
School of Applied and Engineering Physics, Cornell University, Ithaca, NY
Self assembled monolayers (SAM) have been drawing a lot of attention because of its potential use as an ultra-thin resist layer for high resolution electron beam lithography.[1] So far, we demonstrated the ability to pattern nanometer scale features on various substrates by electron beam exposure. We could produce features as small as 5nm on OTS (octadecyltrichlorosilane) monolayer.[2] Now we are testing a new lithography technique that can benefit from ultra-thin resist layers. We have demonstrated that metastable noble gas atom beam(Ar* or He*) can modify and pattern the surface of monolayer. We are also in process of characterizing critical dose and testing effective pattern transfer methods. This work is a ongoing collaboration with Rice university and National Institute of Standard and Technology (NIST).
We have tested the possibility of using neutral metastable atom beam to expose and modify self-assembled monolayer(SAM) film. Metastable neutral atoms of noble gas like Ar* or He* have internal excitation energy of tens of eV, and this energy can be released when these atoms collide with ultra-thin resist layer like SAM. The advantages of using metastable atom, instead of electron or light, are that (1) since they are heavy and have small de Broglie wavelength, they doesn't suffer from diffraction compared to UV lithography, (2) and metastable atoms only interact with the top surface of resist layer, which eliminate scattering problem (proximity effect) of conventional electron beam lithography. (3) After they release their internal excitation energy, they are inert gas atoms and don't have additional effect. It is recently demonstrated that metastable atom can be patterned by a physical proximity mask or laser light.[3]
For an exposure test, OTS(octadecyltrichlorosilane) monolayer on native oxide of Si wafer was prepared here at Cornell University. Detailed information about preparation procedure can be found elsewhere.[1] Then the sample was sent to the Rice University for metastable Ar* atom beam exposure. A proximity exposure mask(grid pattern) was used to compare exposed and unexposed region. Typical dose of metastable Ar* atoms were calculated to be 10^15 ~ 10^16 Ar*/cm2. After the exposure, OTS monolayer loses its hydrophobicity, and the surface characteristic changes. Exposed sample was characterized by atomic force microscopy(AFM) at National Institute of Standard and Technology(NIST) and x-ray photoelectron spectroscopy(XPS) at Cornell University.
For recent publications on this project, press here.
References
[1] M. J. Lercel, Ph.D. Thesis, Cornell University (1996)
[2] M. J. Lercel, H. G. Craighead, A. N. Parikh, K. Seshadri, and D. L. Allara, Appl. Phys. Lett. 68, 1022 (1996)
[3] K. K. Berggren, A. Bard, J. L. Wilbur, J. D. Gillaspy, A. G. Helg, J. J. McClelland, S. L. Rolston, W. D. Phillips, M. Prentiss, and G. M. Whitesides, Science 269, 1255 (1995)
Last modified July 7, 1998