Ankit Vora

Development of polycarbonate-containing block copolymers for thin film self-assembly applications

Access to well-defined materials is one of the key requirements for successful implementation of block copolymer-based lithography for advanced semiconductor nodes. We report on the development of polystyrene-b-polytrimethylene carbonate (PS-b-PTMC) block copolymer (BCP) using organocatalytic ring opening polymerization of trimethylene carbonate (TMC) from hydroxyl-functional polystyrene macroinitiator as a materials candidate for directed self-assembly applications. The impact of organocatalyst choice and the extent of TMC conversion on the quality of PS-b-PTMC BCP were studied using gel permeation chromatography and nuclear magnetic resonance (NMR) spectroscopy techniques. As a direct method to identify PTMC homopolymer content in the resulting BCPs, a new NMR-based technique was developed. Finally, the influence of BCP purity on the thin film morphology was studied using atomic force microscopy and grazing incidence small angle X-ray scattering techniques. Our results indicate that the PTMC homopolymer impurity negatively impacts the thin film morphology, which is extremely important for lithographic applications.

Cross-linkable multi-stimuli responsive hydrogel inks for direct-write 3D printing

Triple stimuli-responsive ABA triblock copolymer hydrogels composed of poly(allyl glycidyl ether)-stat-poly(alkyl glycidyl ether)-block-poly(ethylene glycol)-block-poly(allyl glycidyl ether)-stat-poly(alkyl glycidyl ether) were synthesized using controlled ring-opening polymerization of glycidyl ethers. These polymers form triple stimuli-responsive hydrogels that respond to temperature, pressure (shear-thinning), and UV light. The stimuli-responsive behaviors of the gels were dependent upon the composition and the molecular weight of the ‘A’ blocks of the triblock copolymers. The hydrogels were analyzed rheometrically to characterize their stimuli-responsive properties. The optimized compositions were 3D printed using a direct-write 3D printer to afford robust 3D objects. We anticipate these materials creating new opportunities in the biomedical and biotechnological fields, by enabling the simple and rapid fabrication of 3D hydrogels.

Surface Assembly Configurations and Packing Preferences of Fibrinogen Mediated by the Periodicity and Alignment Control of Block Copolymer Nanodomains.

The ability to control the specific adsorption and packing behaviors of biomedically important proteins by effectively guiding their preferred surface adsorption configuration and packing orientation on polymeric surfaces may have utility in many applications such as biomaterials, medical implants, and tissue engineering. Herein, we investigate the distinct adhesion configurations of fibrinogen (Fg) proteins and the different organization behaviors between single Fg molecules that are mediated by the changes in the periodicity and alignment of chemically alternating nanodomains in thin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). Specifically, the adsorption characteristics of individual Fg molecules were unambiguously resolved on four different PS-b-PMMA templates of dsa PS-b-PMMA, sm PS-b-PMMA, com PS-b-PMMA, and PS-r-PMMA. By direct visualization through high resolution imaging, the distinct adsorption and packing configurations of both isolated and interacting Fg molecules were determined as a function of the BCP template-specific nanodomain periodicity, domain alignment (random versus fully aligned), and protein concentration. The three dominant Fg adsorption configurations, SP∥, SP⊥, and TP, were observed and their occurrence ratios were ascertained on each PS-b-PMMA template. During surface packing, the orientation of the protein backbone was largely governed by the periodicity and alignment of the underlying PS-b-PMMA nanodomains whose specific direction was explicitly resolved relative to the polymeric nanodomain axis. The use of PS-b-PMMA with a periodicity much smaller than (and comparable to) the length of Fg led to a Fg scaffold with the protein backbone aligned parallel (and perpendicular) to the nanodomain major axis. In addition, we have successfully created fully Fg-decorated BCP constructs analogous to two-dimensional Fg crystals in which aligned protein molecules are arranged either side-on or end-on, depending on the BCP template. Our results demonstrate that the geometry and orientation of the protein can be effectively guided during Fg self-assembly by controlling the physical dimensions and orientations of the underlying BCP templates. Finally, the biofunctionality of the BCP surface-bound Fg was assessed and the Fg/BCP construct was successfully used in the Ca-P nanoparticle nucleation/growth and microglia cell activation.

High chi block copolymer DSA to improve pattern quality for FinFET device fabrication

Directed self-assembly (DSA) with block-copolymers (BCP) is a promising lithography extension technique to scale below 30nm pitch with 193i lithography. Continued scaling toward 20nm pitch or below will require material system improvements from PS-b-PMMA. Pattern quality for DSA features, such as line edge roughness (LER), line width roughness (LWR), size uniformity, and placement, is key to DSA manufacturability. In this work, we demonstrate finFET devices fabricated with DSA-patterned fins and compare several BCP systems for continued pitch scaling. Organic-organic high chi BCPs at 24nm and 21nm pitches show improved low to mid-frequency LER/LWR after pattern transfer.

Directed self-assembly of topcoat-free, integration-friendly high- x block copolymers

To extend scaling beyond poly(styrene-b-methyl methacrylate) (PS-b-PMMA) for directed self-assembly (DSA), high quality organic high-x block copolymers (HC series) were developed and applied to implementation of sub-10 nm L/S DSA. Lamellae-forming block copolymers (BCPs) of the HC series showed the ability to form vertically oriented polymer domains conveniently with the in-house PS-r-PMMA underlayers (AZEMBLY EXP NLD series) without the use of an additional topcoat. The orientation control was achieved with low bake temperatures (≤200 °C) and short bake times (≤5 min). Also, these process-friendly materials are compatible with existing 193i-based graphoepitaxy and chemoepitaxy DSA schemes. In addition, it is notable that 8.5 nm organic lamellae domains were amenable to pattern development by simple dry etch techniques. These successful demonstrations of high-x L/S DSA on 193i-defined guiding patterns and pattern development can offer a feasible route to access sub-10 nm node patterning technology.

Contrast enhanced diffusion NMR: quantifying impurities in block copolymers for DSA

Block-copolymers (BCPs) offer the potential to meet the demands of next generation lithographic materials as they can self-assemble into scalable and tailorable nanometer scale patterns. In order for these materials to find wide spread adoption many challenges remain, including reproducible thin film morphology, for which the purity of block copolymers is critical. One of the sources of impurities are reaction conditions used to synthesize block copolymers that may result in the formation of homopolymer as a side product, which can impact the quality and the morphology of self-assembled features. Detection and characterization of these homopolymer impurities can be challenging by traditional methods of polymer characterization. We will discuss an alternate NMR-based method for the detection of homopolymer impurities in block copolymers – contrast enhanced diffusion ordered spectroscopy (CEDOSY). This experimental technique measures the diffusion coefficient of polymeric materials in the solution allowing for the ‘virtual’ or spectroscopic separation of BCPs that contain homopolymer impurities. Furthermore, the contrast between the diffusion coefficient of mixtures containing BCPs and homopolymer impurities can be enhanced by taking advantage of the chemical mismatch of the two blocks to effectively increase the size of the BCP (and diffusion coefficient) through the formation of micelles using a cosolvent, while the size and diffusion coefficient of homopolymer impurities remain unchanged. This enables the spectroscopic separation of even small amounts of homopolymer impurities that are similar in size to BCPs. Herein, we present the results using the CEDOSY technique with both first generation BCP system, poly(styrene)-b-poly(methyl methacrylate), as well as a second generation high-χ system.