In the last year our Solid Immersion Lloyd's Mirror Interference Lithography (SILMIL) system has proved to be a
successful tool for evanescent interferometric lithography (EIL). The initial goal was to use SILMIL in conjunction with
the surface plasmon polariton (SPP) surface states at the resist-metal interface. Through this resonance, we aimed to
counter the decay of evanescent images created using EIL. By analyzing the theory in greater detail we were able to
develop a better understanding of the resonance phenomena. In this paper, details of the design of SILMIL and how one
may utilize it to produce ultra-high numerical apertures (NAs) are given, as well as an introduction to the resonance
phenomena and the mechanism behind it. We introduce a new method that requires a gain medium (one that has a
negative loss) to achieve significant enhancements, and present an effective gain medium by using a high-index
dielectric on low-index media. We present results at λ = 405 nm using such an effective gain medium and also provide a
feasible design example at the lithography standard λ = 193 nm.
Evanescent-wave imaging is demonstrated using solid-immersion Lloyd's mirror interference lithography at λ = 325 nm to produce 44-nm half-pitch structures (numerical aperture, NA = 1.85). At such an ultrahigh NA the image depth is severely compromised due to the evanescent nature of the exposure, and the use of reflections from plasmonic underlayers is discussed as a possible solution. Simulations and modeling show that image depths in excess of 100 nm should be possible with such a system, using silver as the plasmonic material. The concept is scalable to 193 nm illumination using aluminium as the plasmonic reflector, and simulation results are shown for 26-nm half-pitch imaging into a 37-nm thick resist layer using this scheme.
Evanescent-wave imaging is demonstrated using solid-immersion Lloyd's-mirror interference lithography (SILMIL) at
λ = 325 nm to produce 44-nm half-pitch structures (numerical aperture, NA = 1.85). At such an ultra-high NA the image
depth is severely compromised due to the evanescent nature of the exposure, and the use of reflections from plasmonic
under-layers is discussed as a possible solution. Simulations and modelling show that image depths in excess of 100 nm
should be possible with such a system, using silver as the plasmonic material. The concept is scalable to 193 nm
illumination using aluminium as the plasmonic reflector, and simulation results are shown for 26-nm half-pitch imaging
into a 37-nm thick resist layer using this scheme.
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