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 et.al. 
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.
 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).