(573c) Synthesis and Self-Assembly of a New High-? Block Copolymer: Ptbs-b-Phema

Block copolymers (BCPs) have the ability to microphase separate into a variety of periodic morphologies (e.g. spheres, cylinders, lamellae) with a feature-to-feature spacing (pitch) ranging from 5 to 100 nm. In particular, cylindrical and lamellae morphologies are of interest to the microelectronics industry since they can be used as creating masks for nanofabrication of contact holes and line-space patterns, respectively. As the industry tackles the challenges of continuing Moore’s Law, BCPs offer an alternative route to more expensive pathways such as Extreme Ultra-Violet Light lithography (EUVL). The pitch of a BCP is dependent on both the interaction parameter (χ) and the degree of polymerization (N), with a much stronger dependence on the degree of polymerization. Therefore, in order to reach small feature sizes and pitches in the microphase block copolymer assembly, a low N and a high χ are required. Ideally a BCP will be coated on a substrate and raised above its glass transition temperature to microphase separate until a defect free state is reached. By using chemically preferential patterned underlayers, these features can undergo directed self-assembly (DSA) where by their features orient in particular directions rather than random. By removing of one of the BCP’s blocks, an etch mask of line-space or contact holes can be produced over a substrate.

Here we report on the synthesis and characterization of a new high-χ BCP, poly(4-tertbutylstyene)-b-poly(2-hydroxyethylmethacrylate) (PtBS-b-PHEMA). The χ for PtBS-b-PHEMA is expected to be large due to the hydrophobic PtBS and hydrophilic PHEMA having a high penalty for interacting with one another. High χ materials not only possess the ability to reach small pitches but they also have a high penalty of defect formation, as any defects lead to increased interaction area between the blocks and an enthalpic penalty for the system. The BCP was synthesized by anionic polymerization of a TBDMS protected hydroxyethyl methacrylate monomer in conjunction with a t-butyl styrene monomer. Small angle X-ray scattering (SAXS) of the bulk BCP shows that it is capable of phase separating into various morphologies (lamellae, cylinders, and gyroids) exhibiting pitches less than 7nm. Investigation into a neutral underlayer for thin films of PtBS-b-PHEMA was also conducted using photo-definable random copolymers with the ability to modulate their surface energy. Thin film self-assembled morphologies were produced via thermal annealing and viewed using SEM and AFM. An overview of this new block copolymer system and the associated materials required to produce DSA patterns of the material will be reviewed.