PROCEEDINGS ARTICLE | September 2, 2009
Proc. SPIE. 7395, Plasmonics: Nanoimaging, Nanofabrication, and their Applications V
KEYWORDS: Surface plasmons, Polymethylmethacrylate, Interfaces, Silver, Atomic force microscopy, Photoresist materials, Photomasks, Aluminum, Reactive ion etching, Semiconducting wafers
We report on experimental realization of the Fang Ag superlens structure [1] suitable for further processing and
integration in bio-chips by replacing PMMA with a highly chemical resistant cyclo-olefin copolymer, mr-I T85 (Micro
Resist Technology, Berlin, Germany). The superlens was able to resolve 80 nm half-pitch gratings when operating at a
free space wavelength of 365 nm.
Fang et al. used PMMA since it enables the presence of surface plasmons at the PMMA/Ag interface at 365 nm and
because it planarizes the quartz/chrome mask. If the superlens is to be integrated into a device where further processing
is needed involving various organic polar solvents, PMMA cannot be used. We propose to use mr-I T85, which is highly
chemically resistant to acids and polar solvents.
Our superlens stack consists of a quartz/chrome grating mask, a 40 nm layer of mr-I T85, 35 nm Ag, and finally 70 nm
of the negative photoresist mr-UVL 6000 (Micro Resist). A 50 nm layer of aluminium on top of the quartz/chrome mask
reflected all light that did not penetrate through the mask openings thereby reducing waveguiding in the top resist layer.
The exposures took place in a UV-aligner at 365 nm corresponding to the excitation wavelength of the surface plasmons
at the mr-I T85/Ag interface. Supporting COMSOL simulations illustrate the field intensity distribution inside the resist
as well as the presence of surface plasmons at the mr-I T85/Ag boundary. AFM scans of the exposed structure revealed
80 nm gratings.
