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Report No.

Electroforming of Ni mold using high-aspect-ratio PMMA microstructures fabricated by proton beam writing

Tanabe, Yusuke*; Nishikawa, Hiroyuki*; Sato, Takahiro; Ishii, Yasuyuki; Kamiya, Tomihiro

We report on Ni electroforming using high-aspect-ratio PMMA microstructures by Proton Beam Writing (PBW). There are several issues to be addressed in the fabrication process of Ni molds with a high-aspect-ratio using the PMMA microstructures. First, the residual PMMA was observed on the sidewall of PMMA master block by increasing the thickness of its master block. Second, the small voids were formed in the Ni molds when the high-aspect ratio PMMA master blocks were used. These problems ware resolved using the PMMA master blocks fabricated by PBW on the condition of the higher dose exposure than ordinal one and using a seed layer of a 600-$$mu$$m thick Cu substrate evaporated on the Si substrate before spin-coating the PMMA film. The 30-$$mu$$m PMMA master block with the aspect ratio of 30 was successfully fabricated using the above procedures. Using this PMMA master block, the Ni mold with 30-$$mu$$m thick on the Cu substrate was successfully electroformed without voids from the observation of the cross section revealed by a FIB. Furthermore, a Ni mold with grids and circle patterns was also successfully fabricated using a 15-$$mu$$m thick PMMA film spin-coated on a Cu substrate. The result of the thermal imprint using the Ni mold demonstrated that the high aspect structure was transferred on a PMMA film without damages of the Ni mold even after many trials.



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