Tuning the strength of chemical patterns for directed self-assembly of block copolymers

Directed self-assembly (DSA) of block copolymers (BCP) via chemo-epitaxy is a potential lithographic solution to patterns of dense features. The LiNe (Liu-Nealey) flow was used to fabricate the chemical pattern, which guides the BCP due to the different wetting behavior of the materials. Fine control of both the chemical pattern chemistry and geometry are important for DSA of BCP. Furthermore, wetting behavior considerations for DSA extend beyond pattern design and include the surrounding region. BCP DSA would be easier to integrate into device design if the patterned region were isolated with a featureless region (horizontal lamellar BCP assembly) rather than undirected BCP fingerprint structures. This paper addresses two processing steps found to be modifying the guide material. For one, the backfill brush grafts to the cross-linked polystyrene (XPS), albeit at a lower rate than the brush grafts to the exposed substrate. Undersaturating the backfill brush only moderately improves the XPS wetting behavior, but also negatively impacts the background region of the chemical pattern. Replacing the brush grafting functionality so that the brush grafts at lower annealing conditions also did not avoid the side reaction between the brush and the XPS. The other step modifying the XPS is the trim etch. Replacing the trim etch process was effective at generating a chemical pattern that can orient the BCP horizontally on a stripe 11 L-0 wide passing through a field of chemical pattern.