Sub-10 nm Nanofabrication via Nanoimprint Directed Self-Assembly of Block Copolymers

Abstract

Directed self-assembly (DSA) of block copolymers (BCPs), either by selective wetting of surface chemical prepatterns or by graphoepitaxial alignment with surface topography, has ushered in a new era for high-resolution nanopatterning. These pioneering approaches, while effective, require expensive and time-consuming lithographic patterning of each substrate to direct the assembly. To overcome this shortcoming, nanoimprint molds--attainable via low-cost optical lithography--were investigated for their potential to be reusable and efficiently template the assembly of block copolymers (BCPs) while under complete confinement. Nanoimprint directed self-assembly conveniently avoids repetitive and expensive chemical or topographical prepatterning of substrates. To demonstrate this technique for high-resolution nanofabrication, we aligned sub-10 nm resolution nanopatterns using a cylinder-forming, organic-inorganic hybrid block copolymer, polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Nanopatterns derived from oxidized PDMS microdomains were successfully transferred into the underlying substrate using plasma etching. In the development phase of this procedure, we investigated the role of mold treatments and pattern geometries as DSA of BCPs are driven by interfacial chemistry and physics. In the optimized route, silicon molds treated with PDMS surface brushes promoted rapid BCP alignment and reliable mold release while appropriate mold geometries provided a single layer of cylinders and negligible residual layers as required for pattern transfer. Molds thus produced were reusable to the same efficacy between nanoimprints. We also demonstrated that shear flow during the nanoimprint process enhanced the alignment of the BCP near open edges, which may be engineered in future schemes to control the BCP microdomain alignment kinetics during DSA.

From Self-Assembled Monolayers to Coatings: Advances in the Synthesis and Nanobio Applications of Polymer Brushes

“…A typical example of this grafting method is a thermally activated reaction of the hydroxyl group at the chain end with the silanol group on the surface of the native oxide of the silicon wafer (Figure 2a) to form an ether bond [2,41]. Guo et al showed that a chain density (0-0.61 chains/nm 2 ) for low Mw polystyrene (PS) brush on a silicon substrate can be achieved by varying annealing temperature (110 to 150 °C) and time (s to days) [39] (Figure 2b).…”

Monitoring Thermally Induced Cylindrical Microphase Separation of Polystyrene-<i>block</i>-poly(methyl methacrylate) by Atomic Force Microscopy

“…The surface morphologies of annealed films were observed in dynamic force mode using an atomic force microscope (SII S-image) and cantilevers (Olympus OMCL-AC200TS-R3). PS-OH with Mn = 3,200 g mol -1 was purchased from Polymer Source Inc. to prepare silicon substrates modified with PS-OH [7]. A toluene solution containing 1.0 wt% PS-OH was spincoated onto a bare silicon substrate at 3,000 rpm for 30 seconds.…”

“…Directed self-assembly (DSA) using thin films of block copolymers (BCPs) is one of promising lithographic processes to miniaturize electronic components less than 20 nm, because BCPs self-assemble into periodic nanostructures at large areas [1][2][3][4][5][6][7]. The relationships between chemical and topological guiding pattern and assembled BCP morphology have been investigated [8][9][10].…”

Nanopatterns Produced by Directed Self-Assembly in Block Copolymer Thin Films

“…Graphoepitaxy alone can also unidirectionally align line patterns and organize spherical domains. Use of faceted surfaces [95] and 1D groove templates [52], due to entropic effects, as well as nanoimprint lithography [96,97] (NIL), due to surface effects on the vertical groove walls, are efficient techniques to orient BCP nanostructures without requiring macromolecule-scale prior patterning. In the case of reconstructed sapphire surfaces, the atomic crystalline ordering of the substrate can be transferred, over multiple length scales, to the block copolymer microdomains, via facets regular pattern.…”