Resist evaluation for Ni mold fabrication and proton beam writing

In our experiments, we use different photoresists for proton beam writing and mold fabrication. We have fabricated Ni mold with structures down to 500 nm. We first use a fine focused proton beam to expose different photoresists, Polymethyl Methacrylate (PMMA), AR-P 3250 and ma-N 2410. After development and nickel sulfamate electroplating, the structures were faithfully transferred from the photoresists to Ni molds.

Graphical abstractFig. 1 A schematic overview of the process steps in Ni mold fabrication using PBW, (a) Coating the Si wafer with Cr and Au as seed layer for electroplating, (b) Resist coating, (c) PBW using 1 MeV protons, (d) Resist development, (e) Ti coating as a second seed layer for Ni electroplating, (f) Ni electroplating and (g) Mold release. We fabricated integral Ni molds featuring nano-pillars in Ni with PMMA and PBW. The Ni pillars have smooth sidewalls and have 3 aspect ratio which is challenging to achieve in integral Ni molds used for nano-imprinting technique. In addition, we have demonstrated the suitability of PBW in AR-P 3250 and ma-N 2410. Structures down to 500 nm in width were well fabricated in 4 μm and 1 μm thick resists respectively. AR-P 3250 resist is special since it requires a flood UV exposure after PBW to guarantee resist removal during development. Optimized balance between proton dose and UV exposure results in well defined resist structures with smooth and vertical sidewalls. The PBW patterned resist structures were successfully transferred to Ni using electroplating and all the resists can be easily removed from the Ni replica after plating, which enables the fabrication of a high quality Ni mold with high aspect ratio and highly vertical and smooth sidewalls.Figure optionsDownload full-size imageDownload as PowerPoint slide