Fiber based interference lithography for large-area nanopatterning

Abstract

The research work during my MPhil study, a fiber optic interference lithography system, is concluded and presented in this thesis.

The first part of this thesis introduces the establishment of this system, which is named All-Fiber Interference Lithography (AFIL) due to its main novelty and advantages. These features benefit from fiber-optic components, instead of discrete optical components which tend to be bulky, expensive and vulnerable. As a result, the flexibility and usability of the two-beam laser interference lithography (LIL) could be greatly enhanced. A novel interference fringe stabilization technique that directly moves a piezoelectric actuated stage carrying one of the two fiber ends to compensate the relative phase shifts between two laser beams, was also realized by the hard ware circuits and software programming, so as to enable stable and long-time exposure.

The second part of this thesis presents the systematic fabrication results. Two 2-inch diameter photoresist samples were fabricated with and without relative light phase stabilization. In addition to the atomic force microscopy (AFM) characterizations at different spots on the two samples, the relative phase shifts during the exposure and the light intensity distribution profiles were considered together to simulate the contrast of the patterns at different spots. Moreover, grating and complex periodic nanostructures with pitches as small as 240 nm were fabricated in photoresist coated on silicon and glass substrates with size up to 4-inch diameter. Challenges and operation procedures to obtain high-quality nanopatterns using AFIL are also emphasized in this part.

The last part of this thesis briefly demonstrates a number of applications. The molds of novel three-level surface enhanced Raman spectroscopy (SERS) substrates were fabricated by double AFIL exposure, and followed by silver evaporation and ultraviolet nanoimprint lithography (UV-NIL) pattern transfer. The SERS signal and enhancement performance were evaluated. The AFIL photoresist nanopatterns on indium tin oxide (ITO) glass substrates could act as masks to electroplate nanostructured nickel for making high-temperature thermal nanoimprint molds. Besides, the soft lithography mold was fabricated through transferring the photoresist nanopatterns to Polydimethylsiloxane (PDMS).