Swift nanopattern formation of PS-b-PMMA and PS-b-PDMS block copolymer films using a microwave assisted technique.

Microphase separation of block copolymer (BCPs) thin films has high potential as a surface patterning technique. However, the process times (during thermal or solvent anneal) can be inordinately long, and for it to be introduced into manufacturing, there is a need to reduce these times from hours to minutes. We report here BCP self-assembly on two different systems, polystyrene-b-polymethylmethacrylate (PS-b-PMMA) (lamellar- and cylinder-forming) and polystyrene-b-polydimethylsiloxane (PS-b-PDMS) (cylinder-forming) by microwave irradiation to achieve ordering in short times. Unlike previous reports of microwave assisted microphase segregation, the microwave annealing method reported here was undertaken without addition of solvents. Factors such as the anneal time and temperature, BCP film thickness, substrate surface type, etc. were investigated for their effect of the ordering behavior. The microwave technique was found to be compatible with graphoepitaxy, and in the case of the PS-b-PDMS system, long-range translational alignment of the BCP domains was observed within the topographic patterns. To demonstrate the usefulness of the method, the BCP nanopatterns were turned into an 'on-chip' resist by an initial plasma etch and these were used to transfer the pattern into the substrate.

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.

Polymer nanostructures in sub-micron lithographically defined channels: film-thickness effects on structural alignment of a small feature size polystyrene-polyisoprene-polystyrene block copolymer.

The use of phase separation in block copolymer systems to generate regular nanopatterns at surfaces may be an alternative to advanced photolithography. Here, substrates with photolithographically defined rectangular channels (of depth 60 nm and widths 166-433 nm) are used to direct nanoscale phase separation of a polystyrene--polyisoprene--polystyrene (PS-PI-PS) block copolymer into aligned periodic superstructures. This nanoscale phase separation results in the rapid formation of parallel and narrow polystyrene (PS) cylinders orientated in a 2D hexagonal arrangement within a polyisoprene (PI) matrix for the polymer composition used here. The PS-PI-PS system is shown to be extremely amenable to simple processing methods allowing precise and homogeneous coating of the substrates. Effects of polymer film thickness are investigated in depth, given that polymer film thickness plays an essential role in the orientation/architecture of the structure formed. It was observed that control of film thickness can determine the orientation of cylinders (parallel or vertical) with respect to the substrate surface. In films where the PS cylinders are aligned parallel to the substrate surface careful control of the processing parameters facilitates the fabrication of regular multi-layer systems ( layers of cylinders) within the channel. The directional effect imposed by the channels is not limited to polymer nanostructures within the channels as long-range order and alignment can be observed at film thicknesses that extend above the channels and onto the outer surface of the substrate. However, as thickness increases, this 'directing' effect conferring alignment is lost.