Fabrication of sub-50 nm critical feature for magnetic recording device using electron-beam lithography

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We report an electron-beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio (AR) for the nanofabrication of magnetic thin-film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we coated a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat PMGI layer was easily and more quickly dissolved than the top resist layer, so it completely cleared the trench during the develop process. In addition, a vertical sidewall at the bottom of the narrow trench was achieved by controlling the processing conditions, e.g., bake temperature and thickness of the dissolution layer. All of these allowed us to facilitate plating the narrow trench with a high magnetic moment material. In this work, narrow trenches were electroplated with both 1.0 T NiFe and 1.8 T CoNiFe alloys. We demonstrated the capability of fabricating narrow electrodeposited magnetic write top pole structures with a critical dimension (CD) of 30 nm in a 0.24 μm resist (AR=8:1) and a CD of 22 nm in a 0.11 μm resist (AR=5:1).