Selective Chain Mobility Control of a Self-Assembled Gradient Block Copolymer

Ultra-high-resolution patterns have become necessary for the development of semiconductor integrated circuits, and extreme ultraviolet lithography (EUVL) is a leading candidate for the mass production of sub-10nm patterns. However, EUVL has stochastic issues that lead to the formation of defects such as bridges, broken lines, and missing holes. As a solution, directed self-assembly (DSA) of block copolymers (BCPs) can be utilized for the formation of a defect-free encapsulation layer on EUV pattern masks.<br/>To achieve sub-10 nm patterns, BCPs with high Flory-Huggins parameters (χ) are generally required for high quality pattern resolution. However, although high-χ BCPs can be obtained, it is challenging to obtain aligned patterns due to their slow self-assembly kinetics. As an alternative, gradient BCPs are advantageous for high resolution patterns due their rapid self-assembly kinetics. A gradient block consists of gradual composition change from the block junction region to the tail, which creates enough surface energy difference between the polymer blocks to energetically drive perpendicular lamellar formation. Yet, although EUV-scale patterns can be achieved with gradient BCPs, the χ values are not sufficiently high for low roughness. Therefore, a new method for the treatment of patterned BCPs is required for the improvement of pattern quality.<br/>Here, we suggest a simple and novel treatment method that selectively increases the mobility of block junction polymers of gradient BCPs using a pinpoint solvent vapor treatment system. For demonstration, we newly synthesized a styrene (S)/2,3,4,5,6-pentafluorostyrene (PFS) gradient with an Si-containing 4-(tert-butyldimethylsiloxy)-styrene (4BDSS) copolymer block (P(S-g-PFS)-b-P4BDSS) via reversible addition-fragmentation chain-transfer polymerization. PPFS and P4BDSS form the block junctions, and the key to the pinpoint solvent vapor treatment system is to selectively provide solvent vapor-induced mobility to PPFS chains in metaphase after annealing. Solvents with high swelling ratios and solubility parameters similar to those of the polymers were chosen for solely targeting PPFS. When the solvents plasticize the target polymers, it leads to the reduction of the effective glass transition temperature of PPFS whereas P4BDSS remains unaffected. While it is challenging to synthesize BCPs with high χ values, this simple pinpoint solvent vapor treatment system provides a universal method for increasing the morphology quality of various self-assembled BCP patterns. Ultimately, the pinpoint treatment method resolves the stochastic issues of EUV-scale BCP patterns, on which an encapsulation process is performed for EUV-mask formation.