Development of Strategies to Improvement Ordering and Perpendicular Alignment of Cylinder Phase Block Copolymers Used as Templates for Bit Patterned Media

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 noise level in such media is significantly impacted by the precision of the ordering of the individual bits and by the narrowness of their size distribution. Block copolymers that phase separate on the appropriate length scale are one method of pattern generation that is receiving considerable attention. For cylinder forming block copolymer phases the ordering and degree of perpendicular alignment is largely determined by the matching of the substrate surface to the block copolymer. If the chemical properties of the substrate surface match the average for the block copolymer, then thin films of the block copolymer align perpendicularly on annealing. Although there are a number of examples where the substrate surface fortuitously matches the block copolymer, in general an orienting layer is necessary to provide the appropriate match. The most popular approach has been to synthesize a random copolymer with the same average composition as the block copolymer. In order to produce suitably thin orienting layers it has been necessary to chemically tether the random copolymer to the substrate. Previously used chemistry has not been suitable for noble metal substrates such as platinum. We have been developing an alternate approach using thiol functional groups which we anticipate will be more suitable for Pt capped substrates.