Team Members:

Mr. Rabih B. Zaouk
Mr. Benjamin Park

Research Summary:

1. Sub-micron Particle-Based Lithography Background:

Conventional projection lithography is limited by optical diffraction[1]. The smallest feature size achievable with conventional projection lithography techniques is approximately the length of the wavelength of the light source. With STM, electron-beam lithography, or other sequential writing schemes, smaller features can be defined, but these technologies are expensive to implement because of the serial nature of these schemes. We hope to develop a method of defining nanoscale features while retaining the ability to scale in a parallel manner. By using particles close to the substrate we are not limited by diffraction limits, (This has been demonstrated with near-field scanning optical microscopy[2]) and we hope to be able to parallelize the process.

2. Recent results:

Particle-Based Lithography is a novel lithography technique being developed by our group. The novelty lies in the use of a particle transported in a liquid solution as a transducer for the lithographic marking step. Different methods (electro osmosis[3], electrophoresis, optical trapping, Local area Melting Micro-Manipulation (LMMM)[4][5], magnetic manipulation, pressure-based movement, electrostatic manipulation, heat convective flows, acoustokinetic movement, etc.) can be used to guide the motion of a particle suspended in a liquid. The path of the particle is recorded on the underlying substrate (photosensitive SAM , polymer photoresist, silver halide, antibody layers, etcd?). In order to trace particle paths along the surface, several methods of sensitization are being investigated: Photochemical, photo electrochemical, electrochemical, biological, plasmonics[6], near-field enhanced laser irradiation[7], using various enzymes, etc...

Fig 1. (Left) an array of microelectrodes fabricated using standard photolithographic techniques surrounding a web of nanopatterns

Fig 2. (Right) a particle moving on top of a substrate and inducing a submicron wide surface change

Nanomanipulation:

A crucial element in the proposed lithography is the transport of the particle. Trapping of single microparticles using dielectrophoresis [8] followed by electro osmosis is one of the methods we are currently investigating. Preliminary experiments are being conducted as a step towards getting a good hands on comprehension of the parameters that come into play. It seems that of the electrokinetic methods available, dielectrophoresis and electroosmosis scale more favorably compared to electrophoresis.The scaling of the particles and the electrodes tend to cancel out, allowing further scaling [9]. Electrophoresis of charged molecules on a microchip platform is shown in the movie below. (It may seem slow because the video was captured in real time.) Initial experiments utilizing electroosmosis have also been conducted.

Click for real time accumulation movie

We have used pyrolysed SU-8 to create high aspect ratio carbon electrode arrays [9]. Figure 3 shows a high aspect ratio carbon electrode array used for dielectrophoretic trapping. Figure 4 shows the electrodes trapping a cluster of 9.63 micron beads.

Fig. 3. Full view and close-up of a high aspect ratio pyrolysed carbon electrode array used for dielectrophoretic trapping

Fig. 4. Cluster of 9.63 micron beads trapped in a high aspect ratio carbon electrodedielectrophoretic trap

We have found that photographic film can be used as a rapid and inexpensive tool for detecting movement and location of weak luminescent particles. Calculations show that film is 8 orders of magnitude more sensitive than conventional positive photoresist! [9]. Exposure patterns from single phosphorescent particles on Kodak TMAX p3200 professional film is shown in Figure 5. Conventional az1827, az1808 photoresist was not sensitive enough to resolve any patterns due to these particles.

Fig. 5. Exposure patterns from single phosphorescent particles (approx. 40um in diameter) on
Kodak TMAX p3200 professional film. (The exposure time was 30 seconds.)

We have been able to manipulate 2.8 µm (15% iron) and 9.62 µm polystyrene beads in the x-y plane using an array of four electrodes. Just like an etch-a-sketch¢ç toy, we were able to move the particles up, down, left, right, and diagonally (See the movie below)

References:

[1] Madou M, Fundamentals of Microfabrication 2nd edn, 2002

[2] Betzig E and Trautman J K, Single molecules observed by near-field scanning optical microscopy, Science 257 189,1992

[3] H.Morgan, N.G.Green, AC Electrokinetics: colloids and nanoparticles. Research studies press, England.

[4] K. Hirano, R. Ishii, and et al., Application of local temperature control for DNA micromanipulation, 6th Intl. Symp. On Micromachines, pp. 177-182, 1996.

[5] S. Katsura, R.Ishii, M. Nishioka, and et al., Handling of single DNA molecules by controlling the temperature, IEEE Trans. Ind. Appl, pp. 1927-1931, 1996.

[6] Pieter G. Kik et al, Metal nanoparticle arrays for near field optical lithography, SPIE Proceedings, 2002
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[7] Munzer H J, MosbacherM, Bertsch M, Zimmermann J, Leiderer P and Boneberg J, Local field enhancement effects for nanostructuring of surfaces, J. Microsc. 202 129, 2000
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[8] Muller T. Trapping of micrometer and submicrometer particles by high frequency electric fields and hydrodynamic forces. J.Phys. D: appl. Phys.340-349, 1996.

[9] Benjamin Y. Park, Rabih Zaouk, Marc Madou, Validation of lithography based on the controlled movement of light-emitting particles, Proceedings of SPIE Vol. 5374 (Emerging Lithographic Technologies VIII), 2004 (Accepted for publication)