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Abstract

Directed Self-Assembly (DSA) is a promising strategy for quickly and cheaply manufacturing nanoscale features. DSA leverages the natural nanoscale phase separation of materials, which are guided by lithographically defined precise chemical cues. Polystyrene block polymethylmethacrylate (PS-b-PMMA) is ubiquitous for DSA, as the blocks possess equal surface free energy, and a random copolymer brush of the two blocks presents a balanced substrate surface both of which are a necessary prerequisite for achieving through film structures. In a standard process, PS guide stripes at pitches of 70-90 nm, are backfilled with a brush to direct PS-b-PMMA to form features down to ~24 nm pitch (3x density multiplication). In chapter 2, we show how metal – polymer interactions can be used in place of polymer – polymer interactions to provide the necessary chemical cues for DSA. This enables a new kind of self-aligned process in which a patterning layer is thermodynamically driven to align precisely not with a lithographically defined guide or mandrel, but instead with an existing metal – dielectric pattern on an underlying layer. Next in chapter 3, we turn to the DSA hole shrink process, where great effort has been expended to use various wet processes to selectively modify the sidewall and bottoms of lithographically defined template holes to provide the proper chemical cues. Here we demonstrate that ultraconformal initiated chemical vapor deposition (iCVD) can be used as a drop in replacement to conventional wet processes. Finally we turn towards the material itself. The repulsion between PS and PMMA, quantified by the Flory Huggins parameter χ, is too low to achieve sub 24 nm pitch features. Increasing the χ often goes hand in hand with increasing differences in surface free energy, which can be ameliorated only by additional complex processing involving top coats or solvent atmospheres. A further complication is that if the product of χ and the polymer size, N, is too high, defects become trapped. Thus for each pitch desired, there exists a range of acceptable χ. One method to sidestep these limitations is by engineering the polymer microstructure such that these fundamental relationships might be changed. Chapter 4, studies the fundamental physics underlying graft polymer architecture in thin film confinement. Here we discovered substrate interactions can shift materials from perfectly symmetric lamella to cylindrical morphologies. A second method is the use of A-b-(B-r-C) architectures. Chapter 5, outlines a high throughput process to use click chemistry to modify a common platform polystyrene block polybutadiene, to rapidly achieve multiple materials with differing χ, each of which has equal surface energies and is fully compatible with DSA flows. Second we expand to a new platform polystyrene block polyglyicdyl methacrylate which we demonstrate is suitable not just for DSA of 16 nm full pitch features, but can also serve as its own non-preferential brush enabling new self-brushing DSA processes, and can even be modified with etch resistance through the incorporation of silicon. As a result DSA is no longer material limited, and is now enabled for a near infinite diversity of chemistry, providing the potential for further optimization.

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