Investigation of diblock copolymer thin film morphology for nanolithography

The morphologies and ordering in thin polystyrene-polybutadiene (PS-PB) diblock copolymer films are studied on bare silicon and silicon nitride substrates, and also on polymethylmethacrylate (PMMA) coated substrates. The PS-PB copolymers are synthesized to form, in bulk, PB cylinders or spheres in a PS matrix. In thin films, prepared by spin-coating, it is observed that the morphology and ordering of the microdomains are affected by strong wetting constraints and a reduced chain mobility on the substrate. The thinnest self-assembled layer of the copolymer films shows no in-plane microphase separation on both types of substrates. In the case of spherical PS-PB diblock copolymer films, it is observed thatthe ordering of the microdomains is improved in the films on the PMMA substrates, compared to those on the bare substrates. A successful transfer of the microdomain patterns to silicon nitride substrates by a reactive ion etching technique is also demonstrated.