Self-Brushing Block Copolymers for Defect Self-Healing in Directed Self-Assembly

We report the use of a block copolymer (BCP) self-brushing mechanism for surface modification of Si substrates to heal defects in patterns generated for directed self-assembly (DSA). Our model system uses a lamellae-forming BCP consisting of a polystyrene block (PS) and a poly(glycidyl methacrylate) block (PG) that is modified via thiol “click” chemistry with nonpolar and polar thiols (BSH and CSH, respectively) to create a random copolymer (PG(B-r-C)). The ratio of B and C is tuned so that the two blocks of the PS-b-PG(B-r-C) BCP have equal surface energy, wherein the repeat units of the PG(B-r-C) block possess hydroxyl moieties that can irreversibly graft to Si substrates. We show on unpatterned substrates that the self-brushing mechanism can occur on pristine Si substrates as well as substrates previously modified with a penetrable polymer brush. On chemically patterned substrates for DSA with 3x density multiplication, we observe self-healing of defects in aligned polymer patterns through sequential rounds of polymer film deposition. Upon annealing, a BCP monolayer grafts to the substrate and retains the phase separation of the original polymer film, generating a 1:1 chemical guiding pattern. The 1:1 chemical guiding pattern enables healing of defects in films as thick as 60 nm or 3 times the pitch of the BCP. Our system for pattern rectification does not rely on additives to the polymer film, such as end-functionalized homopolymers, and therefore can more easily scale down to lithographically relevant sub-10 nm dimensions.