Barbara Kosmala

Orientation and Alignment Control of Microphase-Separated PS-b-PDMS Substrate Patterns via Polymer Brush Chemistry

Block copolymer (BCP) microphase separation at substrate surfaces might enable the generation of substrate features in a scalable, bottom-up fashion, provided that the pattern structure, orientation, and alignment can be strictly controlled. The PS-b-PDMS (polystyrene-b-polydimethylsiloxane) system is attractive because it can form small features and the two blocks can be readily differentiated during pattern transfer. However, PS-b-PDMS offers a considerable challenge, because of the chemical differences in the blocks, which leads to poor surface wetting, poor pattern orientation control, and structural instabilities. These challenges are considerably greater when line patterns must be created, and this is the focus of the current work. Here, we report controlled pattern formation in cylinder-forming PS-b-PDMS by anchoring different types of hydroxyl-terminated homopolymer and random copolymer brushes on planar and topographically patterned silicon substrates for the fabrication of nanoscale templates. It is demonstrated that non-PDMS-OH-containing brushes may be used, which offers an advantage for substrate feature formation. To demonstrate the three-dimensional (3-D) film structure and show the potential of this system toward applications such as structure generation, the PDMS patterns were transferred to the underlying substrate to fabricate nanoscale features with a feature size of ~14 nm.

Polystyrene-Polymethylmethacrylate Block Copolymers for Lithographically Assisted Bottom-Up Assembly of Nanostructures

Polystyrene-polymethylmethacrylate (PS-PMMA) block copolymers are well known to exhibit microphase separation to form a series of regular structures with local periodic arrangements of the blocks. By developing films of PS-PMMA within topographically patterned silicon (100) substrates (with photolithographically defined rectangular channels of depth 60 nm and widths 166 – 433 nm) these irregular arrangements form highly periodic structures where the features are parallel to the side walls of the channels. However, the use of silicon substrates leads to problems in processing of these films. PS-PMMA does not wet the surface, and this results in island formation on flat substrates. On channel etched substrates this phenomena ensures that the thickness of the films is irregular and poorly defined alignment is seen. Detailed considerations of this polymer system suggest that feature sizes below 25 nm are not realisable. The results suggest other copolymer systems should be studied.