Lingshu Wan

Directed self-assembly (DSA) of block copolymers (BCP) on lithographically-defined nanopatterned surfaces enhances and augments the resolution and patterning properties of traditional lithographic resists and process flows. In DSA, the period of the chemical pre-pattern (Ls) is typically an integral multiple of the natural period of the BCP (Lo). Although great advances in controlled/living polymerization techniques have been made in recent years, it is still difficult to synthesize BCPs with a given period of nanometer precision. Furthermore, other strategies to formulate BCP materials to target a specific Lo may prove in the long-run to provide more reproducible results in manufacturing. Blending BCP with homopolymers is a simple and effective method to adjust the periods and regulate the volume fractions of the two blocks. Dr. Wan is investigating the DSA of ternary blends of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and its corresponding homopolymers.

The use of topcoats in directing the self-assembly of high-χ (Flory-Huggins interaction parameter) BCPs is very promising and has attracted considerable interest in fabricating sub-10-nm size films. These films can form perpendicular structures via thermal annealing only when the top surface is under a neutral condition, which can be achieved using topcoats. However, the present knowledge of BCP DSA is based on systems without topcoats. Dr. Wan is also working on comparing the dynamics of self-assembly of PS-b-PMMA with and without topcoats.