Application of Cylinder Forming Block Copolymers as Templates for Formation of Bit Patterned and Graded Media
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1032-I05-04
Application of Cylinder Forming Block Copolymers as Templates for Formation of Bit Patterned and Graded Media Vishal Warke1,2, Martin Gerard Bakker1,2, Kunlun Hong3, Jimmy Mays3, and Phillip Britt3 1 Center for Materials for Information Technologies, The University of Alabama, Tuscaloosa, AL, 35487-0209 2 Chemistry, The University of Alabama, Tuscaloosa, AL, 35487-0336 3 Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, TN, 37831 ABSTRACT Bit patterned media, including media fabricated with a gradient in composition, is being developed as a potential path to higher information storage density. The formation of metal nanopillars with 20-30 nm repeat spacing and precisely controlled magnetic properties presents a significant challenge to current fabrication methods. We have been developing cylinder forming block copolymer phases as a method to generate the desired patterns coupled with the processing steps necessary to transfer the pattern into magnetic material. This involves spin coating of the polymer on an appropriate orienting layer, annealing to allow the pattern to form by selforganization of the block copolymer, solvent processing to remove the minority domain, electrodeposition to form a hard mask, followed by ion-milling to transfer the pattern to the magnetic material. We have demonstrated each step in this process and will report on the quality of the patterns achieved. INTRODUCTION Thin films of block copolymers have been used by researchers for the fabrication of nanostructures[1-7]. Block copolymers containing immiscible blocks phase separate in order to minimize the interaction between the immiscible blocks. Block copolymer phase separation is different than phase separation occurring in polymer blends. The polymeric segments in the block copolymers are chemically bonded together, hence only microphase separation occurs. Block copolymers can produce different structures of dimensions from tens of nanometers to hundreds of nanometers. The properties of the block copolymer govern the nature of the generated structures. The shape of the nanostructures generated is governed by the chemical composition (f), degree of polymerization (N) and the interaction between the polymer segments. The interaction between the segments is given by a parameter called “Flory-Huggins parameter (χ).” Higher value of χ indicates higher incompatibility between the polymer segments. The degree of polymerization of the block copolymer also decides the size of the structures generated and the polydispersity index decides the uniformity in the size of the structures[8, 9]. Leibler [10] explained the phase behavior of the block copolymer using χ,N and f. Leibler’s phase diagram of block copolymers showed disordered, hexagonal, BCC and lamellar phases. The gyroid phase was later added by Matsen [11]. Block copolymers need the proper spatial orientation to be used as templates for nanofabrication. Thermodynamically, parallel orientation of the blocks is more favorable.
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