Mechanism and dynamics of block copolymer directed assembly with density multiplication on chemically patterned surfaces

Abstract

In this work, we used scanning electron microscopy ͑SEM͒, in situ coherent small angle x-ray scattering ͑SAXS͒, and Monte Carlo molecular simulation to gain insights into the dynamics of block copolymer directed assembly with density multiplication on chemically patterned surfaces. During directed assembly, it was observed with SEM that poly͑styrene-block-methyl methacrylate͒ initially formed discrete polystyrene domains that lacked long-range order at the free surface. After further annealing, the polystyrene domains gradually coalesced into linear domains that were not registered fully with the underlying chemical pattern. The linear domains could be trapped in metastable morphologies. Finally, the linear polystyrene domains formed perpendicular lamellae in full registration with the underlying chemical pattern. It was revealed with SAXS that scattering peaks characteristic of the period of the chemical pattern appeared and disappeared at the early stages of assembly. Finally, the morphological evolution of directed assembly of block copolymer on chemically patterned surfaces was modeled by molecular simulations.

Engineering the Kinetics of Directed Self-Assembly of Block Copolymers toward Fast and Defect-Free Assembly

“…Many of the transient states that occur during DSA, especially in the early stages of annealing, involve complicated 3D structures that cannot be fully observed with top-down metrology. Previous studies have used X-ray scattering to probe the 3D evolution of structures. , However, X-ray techniques can only capture the averaged structure, and it is very difficult to reconstruct fully the complicated and irregular shapes that exist in transient states. Recently, STEM tomography has been demonstrated as a powerful technique for probing 3D BCP structures, and it is especially suitable for visualizing complex and nonuniform 3D morphologies. ,, We used STEM tomography to study the initial structure immediately following phase separation within 12 s of annealing at 190 °C (Figure a) as well as the stitch morphology formed after 3 min of annealing (Figure b).…”

Fabrication of chevron patterns for patterned media with block copolymer directed assembly

“…We refer to the horizontal direction as the "downtrack" direction. [28][29][30] These defects are propagated away from the transition areas, resulting in some loss of usable area. 1(b), the periodic lines of the chevrons have a constant slope k ¼ (n 2 À 1) 1/2 , with n ¼ 11, and a period L 0 ¼ 27 nm, which is the same as the period of the horizontal lines that define the tracks.…”

Improved block copolymer domain dispersity on chemical patterns via homopolymer-blending and molecular transfer printing

“…It is shown that density multiplication requires longer annealing times to reach equilibrium than directed assembly on one-to-one chemical patterns. [40,55,56] The MTP patterns eliminate the need for density multiplication and shorten the time for directed assembly.…”

“…It is shown that block copolymer directed assembly with density multiplication can partially heal the defects in the underlying chemical patterns, [28] and the resulting block copolymer nanostructures are often complex and three dimensional (3D). [34][35][36][37][38] To achieve defect-free density multiplication, it is required that (i) the thermodynamic energy of the defect-free structures is lower than that of metastable structures, otherwise the block copolymers can be kinetically trapped in metastable states [35,36,[39][40][41] and (ii) the width and the wetting properties of the patterned stripes are controlled to an optimal condition to avoid the formation of complex 3D structures. [33][34][35][36][42][43][44][45] Based on the previous experiments and simulations, the thermodynamic energies of defective and defect-free nanostructures from lamellae-forming block copolymers do not differ significantly from each other, [35,36,39,40] and block copolymers can form complex structures depending on the boundary conditions.…”