Real-time and in situ observation of structural evolution of giant block copolymer thin film under solvent vapor annealing by atomic force microscopy.

An instrumentation technique for real-time, in situ and real space observation of microphase separation was proposed for ultra-high molecular weight block copolymer thin films (1010 kg mol-1, domain spacing of 180 nm) under high solvent vapor swelling conditions. This is made possible by a combination of a homebuilt chamber which is capable of supplying sufficient amount of vapor, and force-distance curve measurements which gives real-time swollen film thickness and allow active feedback for controlling the degree of swelling. We succeeded in monitoring the domain coarsening of perpendicular lamellar structures in polystyrene-block-poly(methyl methacrylate) thin films for eight hours via tapping mode imaging. During the annealing process, the thickness reached a maximum of 8.5 times that of the original film. The series of temporal real space topographic images obtained via this method allowed us to study, for the first time, the growth exponent of the correlation length under solvent vapor annealing.

Dynamic Ordering in High-χ Block Copolymer Lamellae Based on Cross-Sectional Orientational Alignment.

Further development of next-generation block copolymer (BCP) lithography processes is contingent on comprehensive studies of the ordering dynamics of high-χ BCPs that can form sub-10 nm features on thin films. However, quantitative analyses of the degree of ordering on the surface and cross sections of thin films have been difficult to execute. To tackle this challenge, we employ a perpendicular lamella-forming high-χ BCP, poly(polyhedral oligomeric silsesquixone-block-2,2,2-trifluoroethyl methacrylate) (PMAPOSS-b-PTFEMA), and reveal that the high-χ PMAPOSS-b-PTFEMA requires three times the activation energy (Ea) compared to that of poly(styrene-block-methyl methacrylate) (PS-b-PMMA) for defect annihilation, at Ea = 2600 ± 420 kJ mol-1, and a transition from a fast ordering regime with a growth exponent of Φ = 0.30 at lower orientational order parameters (ψ2 < 0.36) to a slow ordering regime with Φ < 0.05 at ψ2 > 0.36, where well-aligned lamellae restrict defect annihilations to enthalpically unfavorable glide mechanisms that require BCP intermixing.

Perpendicular Orientation Control without Interfacial Treatment of RAFT-Synthesized High-χ Block Copolymer Thin Films with Sub-10 nm Features Prepared via Thermal Annealing.

In this study, a series of perpendicular lamellae-forming poly(polyhedral oligomeric silsesquioxane methacrylate-block-2,2,2-trifluoroethyl methacrylate)s (PMAPOSS-b-PTFEMAs) was developed based on the bottom-up concept of creating a simple yet effective material by tailoring the chemical properties and molecular composition of the material. The use of silicon (Si)-containing hybrid high-χ block copolymers (BCPs) provides easy access to sub-10 nm feature sizes. However, as the surface free energies (SFEs) of Si-containing polymers are typically vastly lower than organic polymers, this tends to result in the selective segregation of the inorganic block onto the air interface and increased difficulty in controlling the BCP orientation in thin films. Therefore, by balancing the SFEs between the organic and inorganic blocks through the use of poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) on the organic block, a polymer with an SFE similar to Si-containing polymers, orientation control of the BCP domains in thin films becomes much simpler. Herein, perpendicularly oriented BCP thin films with a χeff value of 0.45 were fabricated using simple spin-coating and thermal annealing processes under ambient conditions. The thin films displayed a minimum domain size of L0 = 11 nm, as observed via atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, directed self-assembly (DSA) of the BCP on a topographically prepatterned substrate using the grapho-epitaxy method was used to successfully obtain perpendicularly oriented lamellae with a half pitch size of ca. 8 nm.