Spontaneous Lamellar Alignment in Thickness‐Modulated Block Copolymer Films

Abstract

Here, spontaneous lamellar alignment in a thickness‐modulated block copolymer film is presented as a facile, scalable, and general approach for creating a highly aligned lamellar morphology. Thickness‐modulated block copolymer films are prepared on neutral surfaces by various methods, such as solution dropping, dewetting‐induced self‐organized patterning, and thermal imprinting. Regardless of the film preparation method, the self‐assembled lamellar domains become spontaneously aligned along the thickness gradient after sufficient thermal annealing. Real‐time AFM imaging reveals that spontaneous alignment occurs through the directional growth of well‐ordered domains along the thickness gradient, which is accompanied by defect dynamics, with vertical linear defects moving from thicker parts of the film towards the thinner ones, reducing their length and thus the associated energy. The mechanism underlying this interesting self‐aligning behavior is provided by a ‘geometric anchoring’ phenomenon, originally envisioned to account for the liquid crystal alignment under a non‐flat geometry of confinement. This novel self‐aligning principle offers a valuable opportunity to control nanoscale alignment in block copolymer films by manipulating the, much larger, microscale morphology.

Wrinkle‐Directed Self‐Assembly of Block Copolymers for Aligning of Nanowire Arrays

“…DSA may be used to eliminate structural defects and register the orientation of nanodomains of chemically or topographically patterned substrates. We previously reported a unique DSA process in which BCP lamellae spontaneously oriented along the thickness gradient in thickness‐modulated BCP thin films . In the present work, sinusoidal wrinkles may enforce a thickness gradient in BCP thin films.…”

“…Lamellar nanodomains in the center of the wrinkle were principally oriented orthogonally to the wrinkle direction (blue and green area on the left and right, respectively). This spontaneous lamellar alignment according to the thickness gradient was caused by ‘geometric anchoring’, which is also observed in liquid‐crystal alignment under non‐flat geometric confinement …”

“…BCP self‐assembly on the wrinkled graphene surface generated highly ordered, defect‐free lamellar nanopatterns with 10‐nm feature sizes. Thickness‐modulated BCP films confined at the wrinkled graphene surfaces enforced geometric anchoring and promoted strict alignment of self‐assembled vertical BCP lamellae in the direction of the film thickness gradient . Further domain‐selective metallization produced highly aligned metal‐nanowire arrays with 10‐nm thickness …”

Atomic Layer Deposition Assisted Pattern Multiplication of Block Copolymer Lithography for 5 nm Scale Nanopatterning

“…Directed self‐assembly (DSA) offers the device‐oriented nanopatterns based on BCP self‐assembly and has triggered enormous attentions for semiconductor lithographic applications . To date, various BCPs with different chemical compositions are explored for DSA process .…”

“…Among them, low χ BCPs, such as polystyrene‐block‐poly(methyl methacrylate) (PS‐ b ‐PMMA), has been extensively employed due to several advantages. Well‐established surface neutralization method readily attains the vertical lamellar or cylinder nanostructures with high aspect ratio via fab‐friendly temperature annealing process . Selective etching of PMMA nanodomains provides vertical side wall profile of nanotemplates, which is greatly beneficial for subsequent pattern transfer .…”