Double-Patterned Sidewall Directed Self-Assembly and Pattern Transfer of Sub-10 nm PTMSS‑<i>b</i>‑PMOST

The directed self-assembly (DSA) of two sub-20 nm pitch silicon-containing block copolymers (BCPs) was accomplished using a double-patterned sidewall scheme in which each lithographic prepatterned feature produced two regions for pattern registration. In doing so, the critical dimension of the lithographic prepatterns was relaxed by a factor of 2 compared to previously reported schemes for DSA. The key to enabling the double-patterned sidewall scheme is the exploitation of the oxidized sidewalls of cross-linked polystyrene formed during the pattern transfer of the resist via reactive ion etching. This results in shallow trenches with two guiding interfaces per prepatterned feature. Electron loss spectroscopy was used to study and confirm the guiding mechanism of the double-patterned sidewalls, and pattern transfer of the BCPs into a silicon substrate was achieved using reactive ion etching. The line edge roughness, width roughness, and placement error are near the target required for bit-patterned media applications, and the technique is also compatible with the needs of the semiconductor industry for high-volume manufacturing

Generating Large Thermally Stable Marangoni-Driven Topography in Polymer Films by Stabilizing the Surface Energy Gradient

Marangoni forces drive a fluid to flow in response to positional differences in surface energy. In thin polymer films, a difference in surface energy between two coincident liquid polymers could offer a useful route to manufacture topographically patterned surfaces via the Marangoni effect. Previously, we have demonstrated a photochemical method using the Marangoni effect for patterning thin polystyrene films. To generalize the approach, a theoretical model that gives the underlying physics of this process was also developed, which further revealed that low viscosities, low diffusivities, and large surface energy gradients favor rapid evolution of large film thickness variations. However, as described by the Stokes−Einstein equation or the Rouse model, low viscosity is generally correlated with high diffusivity in a single-component system. Herein, we report a strategy to decouple film viscosity and diffusivity by co-casting a high molecular weight surface energy gradient creating copolymer (low diffusivity) with a low molecular weight majority homopolymer (high diffusivity and low viscosity), which are miscible with each other. Patterned light exposure through a photomask imposes a patterned surface energy gradient between light-exposed and unexposed regions due to photochemical reactions involving only the low diffusivity component. Upon heating the film to the liquid state, the film materials (primarily the low viscosity homopolymer component) flow from the low to high surface energy regions. This strategy either eliminates or greatly slows dissipation of the prepatterned surface energy gradient while maintaining rapid feature formation, resulting in formation of ca. 500 nm high features within only 30 min of thermal annealing. Furthermore, the formed features are stable upon extended thermal annealing for up to one month. It is found that a ratio of Marangoni forces to capillary forces can provide a predictive metric that distinguishes which scenarios produce features that dissipate or persist

A Photochemical Approach to Directing Flow and Stabilizing Topography in Polymer Films

Coatings and substrates with topographically patterned features will play an important role in efficient technologies for harvesting and transmitting light energy. In order to address these applications, a methodology for prescribing height profiles in polymer films is presented here. This is accomplished by photochemcially patterning a solid-state, sensitized polymer film. After heating the film above its glass transition temperature, melt-state flow is triggered and directed by the chemical pattern. A second light exposure was applied to fully activate a heat-stable photo-crosslinking additive. The features formed here are thermochemically stable and can act as an underlayer in a multilayered film. To exemplify this capability, these films were also used to direct the macroscopic film morphology of a block copolymer overlayer

Structure, Stability, and Reorganization of 0.5 <i>L</i>₀ Topography in Block Copolymer Thin Films

The structure, stability, and reorganization of lamella-forming block copolymer thin film surface topography (“islands” and “holes”) were studied under boundary conditions driving the formation of 0.5 <i>L</i>₀ thick structures at short thermal annealing times. Self-consistent field theory predicts that the presence of one perfectly neutral surface renders 0.5 <i>L</i>₀ topography thermodynamically stable relative to 1 <i>L</i>₀ thick features, in agreement with previous experimental observations. The calculated through-film structures match cross-sectional scanning electron micrographs, collectively demonstrating the pinning of edge dislocations at the neutral surface. Remarkably, near-neutral surface compositions exhibit 0.5 <i>L</i>₀ topography metastability upon extended thermal treatment, slowly transitioning to 1 <i>L</i>₀ islands or holes as evidenced by optical and atomic force microscopy. Surface restructuring is rationalized by invoking commensurability effects imposed by slightly preferential surfaces. The results described herein clarify the impact of interfacial interactions on block copolymer self-assembly and solidify an understanding of 0.5 <i>L</i>₀ topography, which is frequently used to determine neutral surface compositions of considerable importance to contemporary technological applications

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

Directed Self-Assembly of Silicon-Containing Block Copolymer Thin Films

The directed self-assembly (DSA) of lamella-forming poly­(styrene-<i>block</i>-trimethylsilylstyrene) (PS–PTMSS, <i>L</i>₀ = 22 nm) was achieved using a combination of tailored top interfaces and lithographically defined patterned substrates. Chemo- and grapho-epitaxy, using hydrogen silsesquioxane (HSQ) based prepatterns, achieved density multiplications up to 6× and trench space subdivisions up to 7×, respectively. These results establish the compatibility of DSA techniques with a high etch contrast, Si-containing BCP that requires a top coat neutral layer to enable orientation

Photopatternable Interfaces for Block Copolymer Lithography

Directly photopatternable interfaces are introduced that facilitate two-dimensional spatial control of block copolymer (BCP) orientation in thin films. Copolymers containing an acid labile monomer were synthesized, formulated with a photoacid generator (PAG), and coated to create grafted surface treatments (GSTs). These as-cast GST films are either inherently neutral or preferential (but not both) to lamella-forming poly­(styrene-<i>block</i>-trimethylsilylstyrene) (PS-<i>b</i>-PTMSS). Subsequent contact printing and baking produced GSTs with submicron chemically patterned gratings. The catalytic reaction of the photoacid generated in the UV-exposed regions of the GSTs changed the interfacial interactions between the BCP and the GST in one of two ways: from neutral to preferential (“N2P”) <i>or</i> preferential to neutral (“P2N”). When PS-<i>b</i>-PTMSS was thermally annealed between a chemically patterned GST and a top coat, alternating regions of perpendicular and parallel BCP lamellae were formed

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

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