Near-field Lithography

While e-beam lithography has demonstrated high resolution (~10 nm) it is not without its drawbacks, most notably the exceptionally high capital equipment cost. Optical tip-enhanced nano-lithography could obtain the same resolution at a small fraction of the cost.

Future generations of semiconductor circuits will require inspection of features ~30 nm. Tip enhanced imaging has been shown to be effective for determining the structure of nanometer sized structures like carbon nano-tubes. We are developing an optical inspection system for nanometer scale integrated circuits.

System under construction
The system will make use of a solid immersion lens (SIL) as shown in Fig.1. The SIL is used to increase the numerical aperture of a traditional confocal microscope as shown in Fig. 2. A metal particle is added to the face of the SIL to form a resonant enhancement tip as shown in Fig. 3. A more complete description of this system is given by Goldberg [1]

Fig. 1. Solid immersion lens configuration. In configuration (a), a hemispherical lens increase resolution by ~n. A super-SIL has a resolution increase of ~ n^2

Fig. 2. Schematic of Confocal microscope combined with a solid immersion lens.

Fig. 3. Combination of SIL with local field enhancement. (1) Incoming laser light with a mode profile that provides an electric field in its focal region perpendicular to the surface of the optical element, (2) focusing lens, (3) focused laser light, (4) optical element, (5) small structure able to locally enhance the electric field of the incoming laser light, (6) sample surface to be optically interacted with, and (7) localized optical interaction.

Reference: [1] B.B Goldberg, S.B. Ippolito, L. Novotny, Z. Liu, and M.S. Ünlü "Immersion Lens Microscopy of Photonics Nanostructures and QDs," IEEE J. Selected Topics in Quantum Electronics, 8, 1051 (2002).

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