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

Sub-5 nm Anisotropic Pattern Transfer via Colloidal Lithography of a Self-Assembled GdF3 Nanocrystal Monolayer

Patterning materials with nanoscale features opens many research opportunities ranging from fundamental science to technological applications. However, current nanofabrication methods are ill-suited for sub-5 nm patterning and pattern transfer. We demonstrate the use of colloidal lithography to transfer an anisotropic pattern of discrete features into substrates with a critical dimension below 5 nm. The assembly of monodisperse, anisotropic nanocrystals (NCs) with a rhombic-plate morphology spaced by dendrimer ligands results in a well-ordered monolayer that serves as a 2D anisotropic hard mask pattern. This pattern is transferred into the underlying substrate using dry etching followed by removal of the NC mask. We exemplify this approach by fabricating an array of pillars with a rhombic cross-section and edge-to-edge spacing of 4.4 ± 1.1 nm. The fabrication approach enables broader access to patterning materials at the deep nanoscale by implementing innovative processes into well-established fabrication methods while minimizing process complexity.

High-Fidelity, Sub-5 nm Patterns from High-χ Block Copolymer Films with Vapor-Deposited Ultrathin, Cross-Linked Surface-Modification Layers

Despite their capability, sub-10 nm periodic nano-patterns formed by strongly segregating block copolymer (BCP) thin films cannot be easily oriented perpendicular to the substrate due to the huge surface energy differences of the constituent blocks. To produce perpendicular nano-patterns, the interfacial energies of both the substrate and free interfaces should be controlled precisely to induce non-preferential wetting. Unfortunately, high-performance surface modification layers are challenging to design, and different kinds of surface modification methods must be devised respectively for each neutral layer and top coat. Furthermore, conventional approaches, largely based on spin-coating processes, are highly prone to defect formation and may readily cause dewetting at sub-10 nm thickness. To date, these obstacles have hampered the development of high-fidelity, sub-5 nm BCP patterns. Herein, an all-vapor phase deposition approach initiated chemical vapor deposition is demonstrated to form 9-nm-thick, uniform neutral bottom layer and top coat with exquisite control of composition and thickness. These layers are employed in BCP films to produce perpendicular cylinders with a diameter of ≈4 nm that propagate throughout a BCP thickness of up to ≈60 nm, corresponding to five natural domain spacings of the BCP. Such a robust approach will serve as an advancement for the reliable generation of sub-10 nm nano-patterns.

Thermal Approaches to Perpendicular Block Copolymer Microdomains in Thin Films: A Review and Appraisal

Block copolymer thin films are highly versatile and accessible materials capable of producing nanofeatures in the size regime of a few to hundreds of nanometers by a simple spin-coating-and-anneal process. Unfortunately, this simple protocol usually leads to parallel microdomains, which limits the applicability of such nanofeatures. A great deal of effort has been put into achieving perpendicular microdomains, but those that incorporate thermal annealing are arguably the most practical and reproducible in the lab and industry. This review discusses the recent ongoing efforts on various thermal approaches to achieving perpendicular microdomains in order to provide the readers with a toolbox to work with.

Characterizing the Interface Scaling of High χ Block Copolymers near the Order-Disorder Transition

Advancements in the directed self-assembly of block copolymers (BCPs) have prompted the development of new materials with larger effective interaction parameters (χ_e). This enables BCP systems with phase separation at increasingly small degrees of polymerization (N). Very often these systems reside near the order-disorder transition and fit between the weak and strong segregation limits where the behavior of BCP systems is not as thoroughly understood. Utilizing resonant soft X-ray reflectivity (RSoXR) enables both the BCP pitch (L₀) and interface width (w_M) to be determined simultaneously, through a direct characterization of the composition profile of BCP lamellae oriented parallel to a substrate. A series of high χ_e BCPs with χ_e ranging from ≈0.04 to 0.25 and χ_eN from 19 to 70 have been investigated. The L₀/w_m ratio serves as an important metric for the feasibility of a material for nanopatterning applications; the results of the RSoXR measurement are used to establish a relationship between χ_e and L₀/w_m. The results of this analysis are correlated with experimentally established limits for the functionality of BCPs in nanopatterning applications. These results also provide guidance for the magnitude of χ_e needed to achieve small interface width for samples with sub-10 nm L₀.

Straightforward Integration Flow of a Silicon-Containing Block Copolymer for Line-Space Patterning

A promising alternative for the next-generation lithography is based on the directed self-assembly of block copolymers (BCPs) used as a bottom-up tool for the definition of nanometric features. Herein, a straightforward integration flow for line-space patterning is reported for a silicon BCP system, that is, poly(1,1-dimethylsilacyclobutane)-b-poly(styrene) (PDMSB-b-PS), able to define sub 15 nm features. Both in-plane cylindrical (L₀ = 20.7 nm) and out-of-plane lamellar structures (L₀ = 23.2 nm) formed through a rapid thermal annealing-10 min at 180 °C-were successfully integrated using graphoepitaxy to provide a long-range ordering of the BCP structure without the use of underlayers or top coats. Subsequent deep transfer into the silicon substrate using the hardened oxidized PDMSB domains as a mask is demonstrated. Combining a rapid self-assembly behavior, straightforward integration, and an excellent etching contrast, PDMSB-b-PS may become a material of choice for the next-generation lithography.

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-block-pentamethyldisilylstyrene) (PVBD-b-PDSS) is reported. Lamellae-forming PVBD-b-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-b-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.

Isomeric Effect Enabled Thermally Driven Self-Assembly of Hydroxystyrene-Based Block Copolymers

We demonstrate through isomeric effect the modulation of thermal properties of poly(hydroxystyrene) (PHS)-based block copolymers (BCPs). A minimal structural change of substituting 3HS for 4HS in the BCP results in a drastic decrease in T_g, which in turn enables the thin film assembly of the BCP via thermal annealing. We synthesized a series of poly(3-hydroxystyrene-b-tert-butylstyrene) [P(3HS-b-tBuSt)] and poly(4-hydroxystyrene-b-tert-butylstyrene) [P(4HS-b-tBuSt)] BCPs by sequential anionic polymerization of protected 3HS/4HS monomer and tBuSt followed by deprotection. Measured T_g of P(3HS) was ∼20-30 °C lower than P(4HS) of comparable molecular weights. As a result, thermally driven self-assembly of P(3HS-b-tBuSt) BCPs in both bulk and thin film is demonstrated. For P(4HS-b-tBuSt) thermal annealing in thin-film at high temperatures results in poorly developed morphology due to cross-linking reaction of the 4HS block. The smallest periodicity observed for P(3HS-b-tBuSt) was 8.8 nm in lamellar and 11.5 nm in cylindrical morphologies. The functionality of the 3HS block was exploited to incorporate vapor phase metal oxide precursors to generate sub-10 nm alumina nanowires.