Modeling Chemoepitaxy of Block Copolymer Thin Films using Self-Consistent Field Theory

Abstract

Directed self-assembly (DSA) of block copolymers (BCPs) is a promising technology for advanced patterning at future technology nodes. We use Self-Consistent Field Theory (SCFT) to model directed self-assembly (DSA) of PS-PMMA block copolymers on chemically patterned surfaces (chemoepitaxy). We consider the scenario in which the surface is covered by a neutral brush, in which PS-preferential guiding lines are written. The lines have width W and the period of the line pattern is denoted as P. After the DSA process, one expects to see a lamellar pattern with period (P/n), where n is the line multiplication factor. Using SCFT, we investigate the stability of the templated lamellar pattern as a function of (P/L₀) and (W/L₀), where L₀ is the bulk lamellar period. We find that the pattern is most stable if the guiding stripe pattern has a width which is slightly larger than the equilibrium lamellar half-period, and roughly corresponds to (W/L₀) = 0.5-0.6, in agreement with earlier studies. The stability of the pattern also depends on the multiplication factor, n; as n is increased, the free energy differences between various morphologies diminish, making the formation of defects more likely. This has significant impact on the practicality of chemoepitaxy for sub-30 nm line and space applications.