Solid-immersion Lloyd's mirror as a testbed for plasmon-enhanced ultrahigh numerical aperture lithography

Evanescent-wave imaging is demonstrated using solid-immersion Lloyd's mirror interference lithography at lambda = 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. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3624516]