No abstract

This Perspective addresses the current state of block copolymer lithography and identifies key challenges and opportunities within the field. Significant strides in experimental and theoretical thin film research have nucleated the transition of block copolymers “from lab to fab”, but outstanding questions remain about the optimal materials, processes, and analytical techniques for first-generation devices and beyond. Particular attention herein is focused on advances and issues related to thermal annealing. Block copolymers are poised to change the traditional lithographic resolution enhancement paradigm from “top-down” to “bottom-up”.

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.

A new resist system is described which undergoes spontaneous relief image formation. The resist is formulated from end capped poly(phthaladehyde), PPA, and a cationic photoinitiator such as a diaryliodonium or triarylsulfonium metal halide. The extreme sensitivity of the resist is the result of designing for chemical amplification. The desired amplification results from the fact that photolysis of the sensitizer generates acid which catalyzes main chain cleavage of the polyaldehyde. The uncapped polymer is thermodynamically unstable with respect to reversion to monomer at room temperature so a single acid catalyzed scission results in complete depolymerization to volatile monomer. A single radiochemical event is thereby amplified in the sense that it produces an enormous number of subsequent chemical transformations. PPA/onium salt resist films are so sensitive that exposure to low doses of e‐beam, X‐ray or ultraviolet radiation results in complete self development without post‐exposure processing of any kind. The exposed area simply vaporizes.