Deep-UV microsphere projection lithography

Abstract

In this Letter, we present a single-exposure deep-UV projection lithography at 254-nm wavelength that produces nanopatterns in a scalable area with a feature size of 80 nm. In this method, a macroscopic lens projects a pixelated optical mask on a monolayer of hexagonally arranged microspheres that reside on the Fourier plane and image the mask's pattern into a photoresist film. Our macroscopic lens shrinks the size of the mask by providing an imaging magnification of ∼1.86×10(4), while enhancing the exposure power. On the other hand, microsphere lens produces a sub-diffraction limit focal point-a so-called photonic nanojet-based on the near-surface focusing effect, which ensures an excellent patterning accuracy against the presence of surface roughness. Ray-optics simulation is utilized to design the bulk optics part of the lithography system, while a wave-optics simulation is implemented to simulate the optical properties of the exposed regions beneath the microspheres. We characterize the lithography performance in terms of the proximity effect, lens aberration, and interference effect due to refractive index mismatch between photoresist and substrate.

Recent advancement on micro-/nano-spherical lens photolithography based on monolayer colloidal crystals

“…The FDTD simulation results match very well with the SEM image, as shown in Fig. 4f and g, respectively [87]. Multiple exposure SLPL technique is a modification of tilted exposure SLPL technique, to some degree, it just only create redundancy.…”

“…4c and e, respectively [88]. Recently, it was shown that tilted exposure could also be carried out in DUV projection SLPL technique by inducing the formation of a photonic nanojet with different angles of incidence [87]. The FDTD simulation results match very well with the SEM image, as shown in Fig.…”

“…In addition, the perpendicular exposure can also be done by replacing common UV light with DUV source during MCC-based SLPL. Recently, Mohseni et al reported a DUV projection SLPL technique at the wavelength of 254 nm that produces nanopillar arrays in a scalable area [87].…”

“…Mohseni et al reported highly elongated nanopillar arrays on 1 μm SiO 2 /Si substrate with a sub-80 nm feature size via SLPL technique using 254 nm wavelength DUV source, as shown in Fig. 6d [87]. In this method, the DUV source plays an important role in reducing the size of the nanojet and the SiO 2 layer serves as an anti-reflection layer to reduce the interference effect.…”

Geometric effect on photonic nanojet generated by dielectric microcylinders with non-cylindrical cross-sections

“…The photonic nanojet under the three incident wavelengths in the visible light region is also investigated. This adjustable characteristics make photonic nanojet more advantageous in the applications of detecting nano-scale structures or subsurface targets [40][41][42][43]. It is demonstrated that imaging by microcylinders has a advantage of large field-of-view compared to microspheres.…”