A Novel Non-lift-off Block Copolymer Nanolithography Technique for Etch-damage Susceptible Magnetic Materials

Nanolithographic techniques based on self-assembled block copolymer templates offer exceptional potential for fabrication of large-area nanostructure arrays from a wide variety of functional materials. Despite significant progress with control of the template ordering and development of pattern transfer schemes, significant issues exist with common techniques such as lift-off and etching. Here, we demonstrate successful execution of a nanolithographic process based on climate-controlled solvent annealing of easily degradable cylinder-forming poly(styrene-$b$-lactide) block copolymer films that avoids both lift-off, and some of the most challenging aspects of etching. In particular, our overfill/planarize/etch-back scheme leads to retention of robust ferromagnetism even in 24 nm diameter dots of a material (Ni$_{80}$Fe$_{20})$ that is both magnetically soft and susceptible to etch damage. The result is a large-area array of 24 $\pm $ 1.6 nm diameter magnetic nanodots with exceptional hexagonally-close-packed long range order that retain their crystallinity and $\sim $ 70 {\%} of the bulk magnetization. Extensive diffraction, microscopy, magnetometry, and electrical measurements provide detailed characterization of the pattern formation and fidelity. Funded by NSF MRSEC.