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

Abstract

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 χ 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 L = 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.

Direct In Situ Observation of the Early‐Stage Disorder–Order Evolution of Perpendicular Lamellae in Thermally Annealed High‐χ Block Copolymer Thin Films

“…[6] SAXS analysis of thermally equilibrated bulk samples annealed at 110 °C for 24 h revealed scattering peaks located at integer ratios to the first-order Bragg scattering peak and a full-pitch domain spacing of 16.2 nm ( Figure S2, Supporting Information). The PMA-POSS volume fraction was tuned to 31 vol% for forming lamellar structures.…”

“…[5] By using perpendicular lamellar structures on high-χ BCP thin films, line and space (L/S) patterns with sub-10 nm facilitating the formation of perpendicular structures. [6,10,[27][28][29][30] Furthermore, earlier studies have focused on the self-assembly behavior of polystyrene-block-poly(methyl methacrylate) (PSb-PMMA). Despite being the industrial workhorse for BCP lithography, PS-b-PMMA has a low strength of segregation and is incapable of forming sub-10 nm features.…”

“…[6,27,30] The organic-inorganic blocks also increase the segregation strength and etch contrast between the blocks, allowing for the formation of sub-10 nm structures. The similar and low SFEs of both blocks (SFE PTFEMA, 19 °C = 24.0 mJ m −2 , SFE PMAPOSS, 19 °C = 30.4 mJ m −2 ) facilitate the formation of perpendicular lamellae on bare Si substrates without chemically modifying layers via simple thermal annealing.…”

“…[6][7][8] Typically, such BCP thin films are prepared by spin-coating a dilute BCP solution onto silicon (Si) substrates. [6][7][8] Typically, such BCP thin films are prepared by spin-coating a dilute BCP solution onto silicon (Si) substrates.…”

“…[6][7][8] Typically, such BCP thin films are prepared by spin-coating a dilute BCP solution onto silicon (Si) substrates. Furthermore, although chemical and physical guides can be used to alleviate the thin film defectivity, [6,[12][13][14][15] BCP thin films that can meet the industrial requirements of 0.01 defects cm −2 have yet to be developed.The difficulty in obtaining defect-free BCP thin films can be attributed to a lack of understanding and experimental documentation in the early-stage evolution of ordered structures and defects in perpendicular lamellar thin films. [9][10][11] Although perpendicular lamellar structures can be obtained by various annealing processes, high defectivity in the resultant thin films reduces the potential for industrial applications.…”