Directed self assembly of block copolymers using chemical patterns with sidewall guiding lines, backfilled with random copolymer brushes.

Recently, alignment of block copolymer domains has been achieved using a topographically patterned substrate with a sidewall preferential to one of the blocks. This strategy has been suggested as an option to overcome the patterning resolution challenges facing chemoepitaxy strategies, which utilize chemical stripes with a width of about half the period of block copolymer to orient the equilibrium morphologies. In this work, single chain in mean field simulation methodology was used to study the self assembly of symmetric block copolymers on topographically patterned substrates with sidewall interactions. Random copolymer brushes grafted to the background region (space between patterns) were modeled explicitly. The effects of changes in pattern width, film thicknesses and strength of sidewall interaction on the resulting morphologies were examined and the conditions which led to perpendicular morphologies required for lithographic applications were identified. A number of density multiplication schemes were studied in order to gauge the efficiency with which the sidewall pattern can guide the self assembly of block copolymers. The results indicate that such a patterning technique can potentially utilize pattern widths of the order of one-two times the period of block copolymer and still be able to guide ordering of the block copolymer domains up to 8X density multiplication.

The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO2 electroreduction.

This communication examines the effect of the surface morphology of polycrystalline copper on electroreduction of CO(2). We find that a copper nanoparticle covered electrode shows better selectivity towards hydrocarbons compared with the two other studied surfaces, an electropolished copper electrode and an argon sputtered copper electrode. Density functional theory calculations provide insight into the surface morphology effect.

Pattern Transfer of Sub-10 nm Features via Tin-Containing Block Copolymers.

Tin-containing block copolymers were investigated as materials for nanolithographic applications. Poly(4-trimethylstannylstyrene-block-styrene) (PSnS-PS) and poly(4-trimethylstannylstyrene-block-4-methoxystyrene) (PSnS-PMOST) synthesized by reversible addition-fragmentation chain transfer polymerization form lamellar domains with periodicities ranging from 18 to 34 nm. Thin film orientation control was achieved by thermal annealing between a neutral surface treatment and a top coat. Incorporation of tin into one block facilitates pattern transfer into SiO2 via a two-step etch process utilizing oxidative and fluorine-based etch chemistries.

Directed self-assembly of silicon-containing block copolymer thin films.

The directed self-assembly (DSA) of lamella-forming poly(styrene-block-trimethylsilylstyrene) (PS-PTMSS, L0=22 nm) was achieved using a combination of tailored top interfaces and lithographically defined patterned substrates. Chemo- and grapho-epitaxy, using hydrogen silsesquioxane (HSQ) based prepatterns, achieved density multiplications up to 6× and trench space subdivisions up to 7×, respectively. These results establish the compatibility of DSA techniques with a high etch contrast, Si-containing BCP that requires a top coat neutral layer to enable orientation.

Photopatternable Interfaces for Block Copolymer Lithography.

Directly photopatternable interfaces are introduced that facilitate two-dimensional spatial control of block copolymer (BCP) orientation in thin films. Copolymers containing an acid labile monomer were synthesized, formulated with a photoacid generator (PAG), and coated to create grafted surface treatments (GSTs). These as-cast GST films are either inherently neutral or preferential (but not both) to lamella-forming poly(styrene-block-trimethylsilylstyrene) (PS-b-PTMSS). Subsequent contact printing and baking produced GSTs with submicron chemically patterned gratings. The catalytic reaction of the photoacid generated in the UV-exposed regions of the GSTs changed the interfacial interactions between the BCP and the GST in one of two ways: from neutral to preferential ("N2P") or preferential to neutral ("P2N"). When PS-b-PTMSS was thermally annealed between a chemically patterned GST and a top coat, alternating regions of perpendicular and parallel BCP lamellae were formed.

Polarity-switching top coats enable orientation of sub-10-nm block copolymer domains.

Block copolymers (BCPs) must necessarily have high interaction parameters (χ), a fundamental measure of block incompatibility, to self-assemble into sub-10-nanometer features. Unfortunately, a high χ often results from blocks that have disparate interfacial energies, which makes the formation of useful thin-film domain orientations challenging. To mitigate interfacial forces, polymers composed of maleic anhydride and two other components have been designed as top coats that can be spin-coated from basic aqueous solution in the ring-opened, acid salt form. When baked, the anhydride reforms and switches polarity to create a neutral layer enabling BCP feature alignment not possible by thermal annealing alone. Top coats were applied to the lamella-forming block copolymers poly(styrene-block-trimethylsilylstyrene-block-styrene) and poly(trimethylsilylstyrene-block-lactide), which were thermally annealed to produce perpendicular features with linewidths of 15 and 9 nanometers, respectively.