Fine Tuning of Lithographic Masks through Thin Films of PS-b-PMMA with Different Molar Mass by Rapid Thermal Processing

The self-assembly of asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) block copolymer based nanoporous thin films over a broad range of molar mass (M-n) between 39 kg.mol(-1) and 205 kg.mol(-1) is obtained by means of a simple thermal treatment. In the case of standard thermal treatments, the self-assembly process of block copolymers is hindered at small M-n by thermodynamic limitations and by a large kinetic barrier at high M-n. We demonstrate that a fine tuning of the annealing parameters, performed by a Rapid Thermal Processing (RTP) machine, permits us to overcome those limitations. Cylindrical features are obtained by varying M-n and properly changing the corresponding annealing temperature, while keeping constant the annealing time (900 s), the film thickness (similar to 30 nm), and the PS fraction (similar to 0.7). The morphology, the characteristic dimensions (i.e., the pore diameter d and the pore-to-pore distance L-0), and the order parameter (i.e., the lattice correlation length xi) of the samples are analyzed by scanning electron microscopy and grazing-incidence small-angle X-ray scattering, obtaining values of d ranging between 12 and 30 nm and L-0 ranging between 24 and 73 nm. The dependence of L-0 as a 0.67 power law of the number of segments places these systems inside the strong segregation limit regime. The experimental results evidence the capability to tailor the self-assembly processes of block copolymers over a wide range of molecular weights by a simple thermal process, fully compatible with the stringent constraints of lithographic applications and industrial manufacturing.