Christopher J. Ellison

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.