High-Aspect-Ratio Perpendicular Orientation of PS-b-PDMS Thin Films under Solvent Annealing

Abstract

A perpendicular orientation of high-aspect-ratio polystyrene-block-polydimethylsiloxane (PS-b-PDMS) cylindrical and lamellar PDMS microdomains was achieved by solvent annealing and then slowly drying thick PS-b-PDMS films. Perpendicularly oriented microdomains occurred throughout the film thickness, except at the air interface, where a layer of inplane microdomains formed due to the surface energy difference between PS and PDMS. In contrast, thermal annealing produced in-plane orientation throughout the film thickness. The solvent-annealed perpendicular orientation was observed for cylindrical morphology PS-b-PDMS of 16 and 45 kg/mol, where PDMS is the minority block, and lamellar PS-b-PDMS of 43 kg/ mol. To obtain fully perpendicular microdomain patterns, a nonselective high-powered 450 W CF 4 /O 2 reactive ion etching process was performed to remove the top layer of the films. Substrate patterning using electron beam lithography produced local registration of 17 nm period hexagonal cylinder patterns.

Pattern transfer using block copolymers

“…For thicker films (approx. 10 L 0 ), PS-b-PDMS forms mixed morphologies throughout the whole film after annealing [110]. Although cylindrical PDMS domains were aligned parallel to the substrate close to the polymer-air interface, their orientation was normal to the substrate in the middle of the film.…”

“…The control of the orientation of microdomains in PS-b-PDMS is more difficult than in PS-b-PMMA because of the large difference in the surface energies between PS and PDMS. The siliconcontaining PDMS blocks have a lower surface tension (γ PDMS ∼ 20.4 mN m −1 ) than PS blocks (γ PS ∼ 40.7 mN m −1 ) so that PDMS domains selectively segregate to the air-polymer interface during self-assembly [110]. In thin films (approx.…”

Precise Synthesis of Fluorine-containing Block Copolymers via RAFT

“…Recently, silicon-containing BCPs have received much attention due to their high etching contrast and small feature dimensions derived from their component incompatibility [2,3]. However, controlling the orientation of such materials is challenging because silicon-containing BCPs with strong segment-segment interaction generally exhibit disparate polarities and a large difference in the surface free energies between the two blocks.…”

Directed Self-assembly of Topcoat-free, Integration-friendly High-^|^chi; Block Copolymers

“…Many orientation control strategies for generating perpendicularly oriented BCP domains have been implemented with high- BCPs. For example, solvent vapor annealing has been used for orientation control of PS-b-PEO [3], PS-b-PDMS [4], PS-b-P2VP [5], PLA-b-PTMSS [6] and PMS-b-PHOST [7]. Introducing a solvent vapor chamber and kinetics of solvent vapor annealing may complicate DSA processing.…”