Hyo Seon Suh

The directed self-assembly (DSA) process, which integrates self-assembling block copolymer (BCP) films with lithographically pre-defined templates, has been extensively researched as an alternative patterning technique to enhance the resolution beyond the limitation of current technology. This approach, already demonstrated with experiments at the laboratory scale, has now started to move to the line in the commercial manufacturing process. In spite of the significant progress to date in DSA technology, there are still several challenges remaining.

The more well-established BCP DSA process was developed around the principle of thermal annealing, which is the most reliable pathway to induce the self-assembly of block copolymers. Unfortunately, this method only works for the special case where the surface energies of each block are similar at the annealing temperature so both blocks are exposed on the free surface during assembly. Poly(styrene-b-methyl methacrylate), or PS-b-PMMA, meets this criterion but is restricted in its use because the smallest feature size realized by PS-b-PMMA is known as the neighborhood of 20 nm.

Seeking block copolymer systems other than PS-b-PMMA is therefore one of the key issues in further reducing the feature size down to the sub-10 nm scale. However, most other block copolymers exhibit a sizeable difference in surface energy between the blocks, especially for those materials with the properties allowing for formation of smaller features. In this case, the block with the lower surface energy tends to segregate to the free surface of films and precludes the assembly of the desired through-film perpendicularly oriented structures. Dr. Suh is actively investigating many different techniques to identify feasible solutions for realization of sub-10 nm scale features, based on his knowledge of polymer physics and interfaces.