Direct Self-Assembly for Non-Periodic Designs

Previously we investigated a directed self-assembly (DSA) process for fabricating a non-periodic pattern (i.e., wide line) lying in between the periodic line/space patterns. A symmetric poly(styrene-block-methyl methacrylate) (PS-b-PMMA) was employed here, which formed a lamella morphology with the natural period (L0) of 30 nm. Unlike the conventional DSA process, we used ArF resist patterns as the chemical guides, and generated a horizontal lamella on the non-periodic guide pattern as an etch template for fabricating the wide line. Our preliminary results showed that controlling the morphological defects around the boundary between the periodic and non-periodic regions would be crucial for this DSA flow. In this paper, we report on how the width of the non-periodic pattern, W, would affect on the overall self-assembled morphology of PS-b-PMMA on the pre-patterned surface. The experimental results showed that a transition from the perpendicular to horizontal lamella on the non-periodic pattern occurred at W=2.50 L0. It was also revealed from our simulations that at W=1.50 L0, the perpendicular PS-rich domain was not attached to the guide surface; it might be taken off after the removal of PMMA. For W>3.5 L0, the wide line was transferred to the underlying silicon (Si) substrate, but some large defects were observed in the non-periodic region, possibly due to some residues of the neutral materials on top of the ArF guide pattern.