Pattern Transfer of Sub-10 nm Features via Tin-Containing Block Copolymers

Tin-containing block copolymers were investigated as materials for nanolithographic applications. Poly(4-trimethylstannylstyrene-block-styrene) (PSnS-PS) and poly(4-trimethylstannylstyrene-block-4-methoxystyrene) (PSnS-PMOST) synthesized by reversible addition–fragmentation chain transfer polymerization form lamellar domains with periodicities ranging from 18 to 34 nm. Thin film orientation control was achieved by thermal annealing between a neutral surface treatment and a top coat. Incorporation of tin into one block facilitates pattern transfer into SiO_2 via a two-step etch process utilizing oxidative and fluorine-based etch chemistries

Directed Self-Assembly and Pattern Transfer of Five Nanometer Block Copolymer Lamellae

The directed self-assembly (DSA) and pattern transfer of poly­(5-vinyl-1,3-benzodioxole-<i>block</i>-pentamethyldisilylstyrene) (PVBD-<i>b</i>-PDSS) is reported. Lamellae-forming PVBD-<i>b</i>-PDSS can form well resolved 5 nm (half-pitch) features in thin films with high etch selectivity. Reactive ion etching was used to selectively remove the PVBD block, and fingerprint patterns were subsequently transferred into an underlying chromium hard mask and carbon layer. DSA of the block copolymer (BCP) features resulted from orienting PVBD-<i>b-</i>PDSS on guidelines patterned by nanoimprint lithography. A density multiplication factor of 4× was achieved through a hybrid chemo-/grapho-epitaxy process. Cross-sectional scanning tunneling electron microscopy/electron energy loss spectroscopy (STEM/EELS) was used to analyze the BCP profile in the DSA samples. Wetting layers of parallel orientation were observed to form unless the bottom and top surface were neutralized with a surface treatment and top coat, respectively

A Hybrid Chemo-/Grapho-Epitaxial Alignment Strategy for Defect Reduction in Sub-10 nm Directed Self-Assembly of Silicon-Containing Block Copolymers

The directed self-assembly (DSA) of a 20 nm full-pitch silicon-containing block copolymer (BCP), poly­(4-methoxystyrene-<i>b</i>-4-trimethylsilylstyrene), was performed using a process that produces shallow topography for hybrid chemo-/grapho-epitaxy. This hybrid process produced DSA with fewer defects than the analogous conventional chemo-epitaxial process, and the resulting DSA was also more tolerant of variations in process parameters. Cross-sectional scanning transmission electron microscopy (STEM) with electron energy loss spectroscopy (EELS) confirmed that BCP features spanned the entire film thickness on hybrid process wafers. Both processes were implemented on 300 mm wafers initially prepatterned by 193 nm immersion lithography, which is necessary for economic viability in high-volume manufacturing. Computational analysis of DSA extracted from top-down SEM images demonstrates the influence of process parameters on DSA, facilitating the optimization of guide stripe width, guide stripe pitch, and prepattern surface energy. This work demonstrates the ability of a hybrid process to improve the DSA quality over a conventional chemo-epitaxial process and the potential for high-volume manufacturing with high-χ, silicon-containing BCPs

Interfacial Design for Block Copolymer Thin Films

Top coat design, coating, and optimization methodologies are introduced that facilitate the synthesis, application, and identification of neutral top coats for block copolymer (BP) thin films. Polymeric top coat composition, controlled via synthesis, determines interfacial wetting characteristics. Trimethylammonium salts of top coats improve solubility and coating uniformity. A “confined” island and hole test conveniently establishes (non)­preferential wetting at the top coat/BP interface, which depends upon top coat composition. The utility of these three concepts was demonstrated with two high-χ, lamella-forming BPs, poly­(styrene-<i>block</i>-4-trimethylsilylstyrene) (PS-<i>b</i>-PTMSS) having two periodicities <i>L</i>₀ = 18 and 22 nm and poly­(styrene-<i>block</i>-methyltrimethylsilylmethacrylate) (PS-<i>b</i>-PTMSM) with <i>L</i>₀ = 15 nm. The combination of neutral top and bottom interfaces resulted in a perpendicular orientation of lamellae independent of BP film thickness (1–3 <i>L</i>₀) when thermally annealed for 60 s or less

Chronic myelogenous leukemia stem and progenitor cells demonstrate chromosomal instability related to repeated breakage-fusion-bridge cycles mediated by increased nonhomologous end joining

Chromosomal aberrations are an important consequence of genotoxic exposure and contribute to pathogenesis and progression of several malignancies. We investigated the susceptibility to chromosomal aberrations in chronic myelogenous leukemia (CML) progenitors after exposure to ionizing radiation. In normal progenitors, ionizing radiation induced both stable and unstable chromosomal lesions, but only stable aberrations persisted after multiple divisions. In contrast, radiation of chronic phase CML progenitors resulted in enhanced generation of unstable lesions that persisted after multiple divisions. CML progenitors demonstrated active cell cycle checkpoints and increased nonhomologous end joining DNA repair, suggesting that persistence of unstable aberrations was the result of continued generation of these lesions. CML progenitors demonstrated enhanced susceptibility to repeated cycles of chromosome damage, repair, and damage through a breakage-fusion-bridge mechanism. Perpetuation of breakage-fusion-bridge cycles in CML progenitors was mediated by classic nonhomologous end joining repair. These studies reveal a previously unrecognized mechanism of chromosomal instability in leukemia progenitors because of continued generation of unstable chromosomal lesions through repeated cycles of breakage and repair of such lesions