Nanoscale Patterning Via Block Copolymers

An advance in formulating block copolymers (BCPs) may help electronics manufacturers exploit BCP films for making ever smaller circuit features via photolithography (Nano Lett. 2015, DOI: 10.1021/acs.nanolett.5b04602). BCPs can spontaneously form patterns with nanosized features on surfaces. But controlling those patterns is challenging. A BCP with a low χ value, a measure of the blocks’ tendency to segregate, generally cannot form patterns with features smaller than 10 nm. High-χ BCPs can form sub-10-nm features. But the difference in surface energy between the blocks of a high-χ BCP typically causes the blocks to stack parallel to the surface, which buries the pattern, making it useless. For lithographic patterning, the blocks must line up perpendicular to the surface. Dow Chemical’s Phillip D. Hustad and coworkers have shown that using a small amount of a second BCP can solve the alignment problem. One of that BCP’s blocks balances the surface tension that drives the main BCP’s blocks to lie down on the surface, causing them instead to align vertically. The other block keeps the second BCP anchored firmly on top of the main BCP, ensuring that its blocks remain aligned vertically.