Austin P. Lane

Directed Self-Assembly and Pattern Transfer of Five Nanometer Block Copolymer Lamellae

The directed self-assembly (DSA) and pattern transfer of poly(5-vinyl-1,3-benzodioxole-block-pentamethyldisilylstyrene) (PVBD-b-PDSS) is reported. Lamellae-forming PVBD-b-PDSS can form well resolved 5 nm (half-pitch) features in thin films with high etch selectivity. Reactive ion etching was used to selectively remove the PVBD block, and fingerprint patterns were subsequently transferred into an underlying chromium hard mask and carbon layer. DSA of the block copolymer (BCP) features resulted from orienting PVBD-b-PDSS on guidelines patterned by nanoimprint lithography. A density multiplication factor of 4× was achieved through a hybrid chemo-/grapho-epitaxy process. Cross-sectional scanning tunneling electron microscopy/electron energy loss spectroscopy (STEM/EELS) was used to analyze the BCP profile in the DSA samples. Wetting layers of parallel orientation were observed to form unless the bottom and top surface were neutralized with a surface treatment and top coat, respectively.

Real-time structural evolution at the interface of an organic transistor during thermal annealing

Polarization multiplexed vibrational sum frequency generation (PM-VSFG) spectroscopy has been used to monitor the interfacial structure of polymer transistor interfaces in situ during thermal annealing treatments. The evolution of the field-effect carrier mobility is tracked simultaneously with the molecular orientation and ordering of poly(3-hexylthiophene) (P3HT) macromolecules on two different surface types. It is shown that fluorocarbon functionalized silica imparts very different molecular arrangements that avoid kinetic trapping during solution casting. In contrast, bare silica surfaces produce kinetically trapped polymer configurations that can be observed by PM-VSFG to reorient with thermal annealing. The interfacial results are compared to bulk structural changes in P3HT thin films as characterized by differential scanning calorimetry and linear spectroscopies. The electrical performances of these films are more closely correlated with interfacial parameters than the bulk properties of the polymer. In contrast with the bulk measurements, the PM-VSFG studies show that molecules at the organic/dielectric interface are actually less ordered after thermal annealing processes that render them with lower carrier mobilities.

Highly Stretchable Thermoset Fibers and Nonwovens Using Thiol–ene Photopolymerization

In this report, we describe the preparation and characterization of a new class of thermoset fibers with high elongation and elastic recovery. Integrating UV-activated thiol-ene photopolymerization and electrospinning, we demonstrate an environmentally friendly single step approach to convert small monomeric precursor molecules into highly elastic fibers and nonwoven mats. The fibers were derived by in situ photopolymerization of a trifunctional vinyl ether monomer and a tetrafunctional thiol. Although thermosets often offer good chemical and thermal stability, these fibers also have a high average elongation at break of 62%. The elastomeric nature of these vinyl-ether based fibers can be partly attributed to their subambient Tg and partly to the cross-link density, monomer structure, and resulting network homogeneity. Nonwoven mats of these fibers were also stretchable and exhibited a much higher elongation at break of about 85%. These thermoset stretchable fibers could have potential applications as textile, biomedical, hot chemical filtration, and composite materials.

Block copolymers for sub-10nm directed self-assembly lithography (Conference Presentation)

Directed self-assembly (DSA) of block co-polymers (BCPs) is a next-generation lithography technique that shows promise for extending Moore’s Law into the 10 nm regime and below. The minimum size of the features that can be produced by BCPs is controlled by the interaction parameter (chi) and the degree of polymerization (N). We have developed silicon containing BCPs for sub-20 nm line-and-space lithography. These BCPs were synthesized by living anionic polymerization, thermally annealed in thin films between neutral layers to generate the requisite perpendicular orientation [1, 2]. The silicon-containing blocks provide excellent development contrast under both oxidizing and reducing reactive ion etching (RIE) conditions. The developed patterns work well as masks for transfer of the developed patterns into useful substrate materials [3]. Through optimizing the design of the block copolymers and the “hybrid” DSA process [1], we have now obtained 10 nm full pitch gratings. Recently we have studied silicon containing BCPs that incorporate a poly(2-vinylpyridine) block as a path to achieving still higher chi. For example, we have synthesized poly(4-pentamethyldisilylstyrene-block-2-vinylpyridine) (PDSS-b-P2VP) and found that this material has a chi parameter that is significantly higher than that of the BCP used for 10 nm lithography, meaning that even smaller feature sizes should be possible. Neutral top coats and cross-linked surface treatment layers were identified for PDSS-b-P2VP using the island and hole techniques that have been described previously [5]. We have succeeded in demonstrating 8 nm full pitch finger print patterns that are oriented perpendicular to the substrate. These are the smallest patterns we have managed to obtain in our system to date. 1. Blachut, G., et al. Chem. Mater (2016), 28 (24), 8951-8961. 2. Bates C. M., et al. Science (2012), 338 (6108), 775. 3. Azarnouchea, L., et al. J. Vac. Sci. Technol. B (2016) 34 (6), 061602/1-061602/10. 4. Lane A. P., et al. ACS Nano (2017), 11 (8), 7656-7665. 5. Maher, M. J., et al. Chemistry of Materials (2014), 26 (3), 1471-1479.

A progress report on DSA of high-chi silicon containing block co-polymers (Conference Presentation)

We have developed block co-polymers (BCPs) in which one of the blocks incorporates silicon and the other does not [1]. These materials provide access to BCPs with high Flory-Huggins interaction parameters (χ) and dry etch selectivity under reactive ion etching (RIE) conditions to provide Sub-20 nm patterns [2]. Recently we have investigated a hybrid chemo/grapho-epitaxy process that provides 20 nm and 10 nm full pitch patterning and we have transferred these patterns into useful substrates. This hybrid process produced 20 nm DSA with fewer defects with this material than the conventional chemo-epitaxial process. Cross-sectional scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) confirmed that the BCP features span the entire film thickness on hybrid process wafers [3]. We have now succeeded in demonstrating DSA with poly(4-methoxystyrene-block-4-trimethylsilylstyrene) (PMOST-b-PTMSS) aligned by guidelines comprised of cross linked poly(2-vinylpyridine) (Figure a). The process was demonstrated by cross-section analysis to produce features that span the entire BCP film thickness and the introduction of nitrogen into the guide line provides new evidence for the nature of the interaction between the guide lines and the BCP(Figure b). We have also reported the DSA and pattern transfer of poly(5-vinyl-1,3-benzodioxole-block-pentamethyldisilylstyrene) (PVBD-b-PDSS) at 10 nm full pitch. However, in this case, the DSA involved a trade-off between perpendicularity and dislocation defects [4]. Improved brush materials that selectively graft to an etched Cr surface rather than etched imprint resist provide oriented and aligned 5 nm line-and-space patterns that cleanly traverse the full film thickness thickness (Figure c). 1. Bates C. M., et al. Science (2012), 338 (6108), 775. 2. Azarnouchea, L., et al. J. Vac. Sci. Technol. B (2016) 34 (6), 061602/1-061602/10. 3. Blachut, G., et al. Chem. Mater (2016), 28 (24), 8951-8961. 4. Lane A. P., et al. ACS Nano (2017), 11 (8), 7656-i7665.

A method to accelerate creation of plasma etch recipes using physics and Bayesian statistics

Next generation semiconductor technologies like high density memory storage require precise 2D and 3D nanopatterns. Plasma etching processes are essential to achieving the nanoscale precision required for these structures. Current plasma process development methods rely primarily on iterative trial and error or factorial design of experiment (DOE) to define the plasma process space. Here we evaluate the efficacy of the software tool Recipe Optimization for Deposition and Etching (RODEo) against standard industry methods at determining the process parameters of a high density O2 plasma system with three case studies. In the first case study, we demonstrate that RODEo is able to predict etch rates more accurately than a regression model based on a full factorial design while using 40% fewer experiments. In the second case study, we demonstrate that RODEo performs significantly better than a full factorial DOE at identifying optimal process conditions to maximize anisotropy. In the third case study we experimentally show how RODEo maximizes etch rates while using half the experiments of a full factorial DOE method. With enhanced process predictions and more accurate maps of the process space, RODEo reduces the number of experiments required to develop and optimize plasma processes.