Integration of Metallic Nanostructures in Fluidic Channels for Fluorescence and Raman Enhancement by Nanoimprint Lithography and Lift-off on Compositional Resist Stack

Abstract

We present and demonstrate a novel fabrication method to integrate metallic nanostructures into fluidic systems, using nanoimprint lithography and lift-off on a compositional resist stack, which consists of multi-layers of SiO(2) and polymer patterned from different fabrication steps. The lift-off of the stack allows the final nano-features precisely aligned in the proper locations inside fluidic channels. The method provides high-throughput low-cost patterning and compatibility with various fluidic channel designs, and will be useful for fluorescence and Raman scattering enhancement in nano-fluidic systems.

Fig. 1. Schematics of NIL patterning of Au nano-dots in fluidic channels

(a) Fused silica substrate coated with bottom stack of SiO₂/ARC; (b) Micro-fluidic channels defined by photolithography; (c) Micro-channels patterned in bottom SiO₂/ARC layers and fused silica, with photoresist stripped; (d) Middle stack of SiO₂/ARC coated on the substrate; (e) Second photolithography to define the nano-feature patterning window for Au nano-dots; (f) Nanofeature patterning window transferred to middle stack SiO₂/ARC by RIE; (g) Imprint resist coated and planarized on the substrate; (h) Nano-holes patterned in imprint resist by a nano-pillar mold and covered with a Cr mask. (i) Au nano-dots patterned in fluidic channels by evaporation and liftoff.

Fig. 2. Optical images of fabricated micro-channels and nano-feature patterning windows

(a) Micro-channels fabricated in bottom SiO₂/ARC stack and fused silica. (b) Nano-feature windows in middle SiO₂/ARC stack.

Fig. 3. Planarization and nanoimprint on non-flat substrate patterned with fluidic channels

a–b, Optical images of imprinted patterns on: (a) non-planarized substrate, and (b) planarized substrate. c–e, AFM images showing the surface morphologies of: (c) patterned substrate with SiO₂/ARC stacks; (d) planarized substrate with imprint resist, and (e) nano-holes imprinted on planarized substrate.

Fig. 4. Imprint on fluidic channel substrate with a nano-pillar mold

a–b, SEM images of a mold with 60 nm wide nano-pillars: (a) 45° side view, and (b) top view. c–e, SEM images of imprinted patterns in resist on fused silica micro-channel substrate: (c) 45° side view to show the micro-channels and nano-feature patterning window, (d) top view to show the nano-holes, and (e) Cross-sectional view to show the resist, SiO₂/ARC stacks, and fluidic channel in fused silica, with a light blue light indicating the thin bottom SiO₂ layer.

Fig. 5. Fabricated 60 nm diameter Au nano-dots aligned in fluidic channels

a–b, SEM images, (c) optical image of Au nano-dots after liftoff, and (d) optical image of Au nano-dots integrated in a fluidic device.

Fig. 6. SEM images of precisely aligned 115 nm wide fused silica nano-pillars in fluidic channels

(a) high-magnification image of rectangular nano-pillars, and (b) nano-pillar regions selectively patterned in channels and aligned to the channel edge.