Directed Self-Assembly

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1. Sub-10 nm Lithography


Since 1960s, the number of transistors in an integrated circuit has roughly doubled every two years, showing exponential growth in the capabilities of electronic devices. This tendency has been sustained over the past several decades on the basis of continuous advancements in manufacturing technologies including optical lithography. However, photolithography is reaching a physical limit in resolution and thus, alternative technologies such as extreme ultraviolet (EUV) lithography, nanoimprint lithography, interference lithography and directed self-assembly (DSA) are rapidly emerging.

DSA of block copolymers (BCPs) has recently attracted much attention as a promising candidate for the next-generation lithography due to its capacity to provide excellent resolution and scalability. The self-assembly of BCPs, two mutually incompatible polymer chains connected via covalent bonding, can create sub-10 nm periodic patterns with different geometries such as dots, lines, holes, and rings, while even more complex features such as bends, T-junctions, and jogs have already been demonstrated. Based on these promising results, our research efforts have focused on resolving remaining challenges for DSA such as control over defects, resolution, and throughput for next-generation lithography with sub-10 nm resolution.


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 2. Warm Solvent Annealing (WSA)


We reported warm solvent annealing of poly(vinylpyridine-b-dimethylsiloxane) with gigantic χ parameter (1.8 at room temperature) to realize high throughput and superior pattern quality. Due to the gigantic χ parameter, we could achieve thermodynamically low defect density as well as low line edge roughness. Furthermore, by adopting the warm solvent annealing, we demonstrated rapid pattern generation of gigantic-χ due to thermal activation effect during polymer diffusion process.


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  3. Warm Spin Casting (WSC)


We introduce ″in situ nanolithography″ using the warm spin-casting (WSC)-induced self-assembly of high-χ BCPs, enabling the removal of the subsequent annealing process. This concept and realization of in situ DSA pattern formation is synergically assisted by both the residual solvent during spin-casting and the thermal activation. WSC achieves one-step BCP film casting and pattern ordering, which is based on (1) a BCP with a sufficiently large thermodynamic driving force for phase separation and (2) optimized thermal activation during the WSC process in order to provide sufficient chain mobility for self-assembly. We demonstrate that WSC can successfully generate well-aligned cylindrical BCP patterns with a sub-10 nm line width within a spinning time of 30 sec.



  4. Immersion-Induced Self-Assembly (ISA)


The directed self-assembly (DSA) of block copolymers (BCPs) is expected to complement conventional optical lithography due to its excellent pattern resolution and costeffectiveness. Recent studies have shown that BCPs with a large Flory-Huggins interaction parameter (χ) are critical for a reduction of the thermodynamic defect density as well as an increase in pattern density. However, due to their slower self-assembly kinetics, high-χ BCPs typically necessitate solvent vapor annealing, which requires complex facilities and procedures compared to simple thermal annealing. Therefore, our group suggest an immersion-triggered directed self-assembly (iDSA) process and demonstrate the combined advantages of excellent simplicity, productivity, large-area capability, and tunability. We show that the vapor-free, simple immersion of high-χ BCPs in a composition-optimized mixture of nonswelling and swelling solvents can induce the ultrafast (5 min) formation of nanoscale patterns with a pattern size ranging from 8-18 nm. Moreover, iDSA enables the reversible formation of seven different nanostructures from one sphere-forming BCP, demonstrating the outstanding controllability of this self-assembly route.

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The vapor-free immersion treatment (iDSA) in a solvent mixture composed of swelling and nonswelling solvents can successfully facilitate the self-assembly of BCPs for fast and convenient pattern formation in the sub-20 nm regime. The careful control of solvent composition and other parameters provided well-aligned line and dot patterns with dimensions in the range of 8-18 nm. The outstanding simplicity of iDSA stems from the fact that swelling solvent molecules are directly injected from the liquid source into BCP films without the need to generate vapors. Because of the obvious advantages of outstanding simplicity and effectiveness, we expect that the iDSA process has the potential to replace the conventional solvent-vapor-based annealing method.




■ Jong Min Kim, Yong Joo Kim, Woon-Ik Park, Yoon Hyung Hur, Jae Won Jeong, Dong Min Sim, Kwang-Min Baek, Jung Hye Lee, Mi-Jeong Kim, and Yeon Sik Jung*, “Eliminating the Trade-Off between the Throughput and Pattern Quality of Sub-15 nm Directed Self-Assembly via Warm Solvent Annealing”Advanced Functional Materials, 2015, 25, 2, 306-315   [PDF file]

■ Woon Ik Park, Jong Min Kim, Jae Won Jeong, and Yeon Sik Jung*, ”Deep-Nanoscale Pattern Engineering by Immersion-Induced Self-Assembly”, ACS Nano, 2014, 8, 10, 10009-18 [PDF file]

■ Caroline A. Ross*, Karl K. Berggren, Joy Y. Cheng, Yeon Sik Jung,* and Jae-Byum Chan, “Three-Dimensional Nanofabrication by Block Copolymer Self-Assembly”Advanced Materials, 2014, 26, 25, 4386–4396 [PDF file]

■ Woon Ik Park, YongJoo Kim, Jae Won Jeong, Kyungho Kim, Jung-Keun Yoo, Yoon Hyung Hur, Jong Min Kim, Edwin L. Thomas, Alfredo Alexander-Katz & Yeon Sik Jung*, “Host-Guest Self-assembly in Block Copolymer Blends”Scientific Reports, 2013, 3, 3190 [PDF file]