Nanopatterning via Solvent Vapor Annealing of Block Copolymer Thin Films

The self-assembly of block copolymers to generate nanopatterns is of great interest as an inexpensive approach to sub-20 nm lithography. Compared to thermal annealing, solvent vapor annealing has several intriguing advantages with respect to the annealing of thin films of block copolymers, particularly for polymers with high interaction parameters, x and high molecular weights. In this methods paper, we describe a controlled solvent vapor flow annealing system with integrated in situ microscopy and laser reflectometry, as well as a feedback loop that automatically controls the solvent vapor flow rate, based upon real-time calculations of the difference between thickness set point and the observed film thickness. The feedback loop enables precise control of swelling and deswelling of the polymer thin film, the degree of swelling at the dwell period, and preprogrammed complex multistep annealing profiles. The in situ microscope provides critical insight into the morphological evolution of the block copolymer thin films over a broad area of the sample, revealing information about terraced phases, on the scale of tens and hundreds of micrometers, during the annealing process. This device could be a powerful tool for understanding and optimizing solvent annealing by providing multiple sources of in situ information, at both the micro- and nanoscales.