Gordon S. W. Craig

Towards an all-track 300 mm process for directed self-assembly

This study modifies the authors’ previously reported directed self-assembly (DSA) process of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) in order to meet the throughput and material-related requirements of a semiconductor manufacturing environment. It is demonstrated that all of the bottleneck steps in the authors’ DSA process, including the deposition of the cross-linkable mat and the deposition of the brush layer, can be done in minutes on a hot plate in an N2 atmosphere, which simulates the processing environment of a lithography track module. A 25-nm-pitch pattern resulting from a 4:1 density multiplication was demonstrated with a manufacturing-compatible organic solvent. A preliminary uniformity study on 300 mm wafers was also presented. The modified DSA process presents a viable solution to some of the anticipated throughput-related challenges to DSA commercialization and thus, brings integration of DSA within reach of the semiconductor manufacturing industry.

Pattern dimensions and feature shapes of ternary blends of block copolymer and low molecular weight homopolymers directed to assemble on chemically nanopatterned surfaces.

Ternary blends of cylinder-forming polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) and low molecular weight PS and PMMA were directed to assemble on chemically patterned surfaces with hexagonal symmetry. The chemical patterns consisted of strongly PMMA preferential spots, patterned by electron-beam lithography, in a matrix of PS. The spot-to-spot spacing of the chemical patterns (L(s)) was varied between 0.9L(0) and 1.1L(0), where L(0) is the cylinder-to-cylinder spacing of the pure block copolymer in bulk. The homopolymer volume fraction of the blends (ϕ(H)) was varied between 0 and 0.3. In addition, chemical patterns were formed with selected spots missing from the perfect hexagonal array, such that the interpolation of domains between patterned spots could be examined on patterns where the polymer/pattern feature density ranged from 1:1 to 4:1. The assemblies were analyzed with top-down SEM, from which orientational order parameter (OP(o)) values were determined. The SEM analysis was complemented by Monte Carlo simulations, which offered insights into the shapes of the assembled cylindrical domains. It was found that, in comparison to pure block copolymer, adding homopolymer increased the range of L(s) values over which assemblies with high OP(o) values could be achieved for 1:1 assemblies. However, the corresponding simulations showed that in the 1:1 assemblies the shape of the cylinders was more uniform for pure block copolymer than for blends. In the case of the 4:1 assemblies, the range of L(s) values over which assemblies with high OP(o) values could be achieved was the same for all values of ϕ(H) tested, but the domains of the pure block copolymer had a more uniform shape. Overall, the results provided insights into the blend composition to be used to meet technological requirements for directed assembly with density multiplication.

Directed assembly of asymmetric ternary block copolymer-homopolymer blends using symmetric block copolymer into checkerboard trimming chemical pattern

Here, the authors studied the directed assembly of the asymmetric ternary blends, composed of polystyrene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) and the corresponding PS and PMMA homopolymers, on a checkerboard chemical pattern which was fabricated by e-beam lithography, controlling the periodicity (LS), length (D), and spacing of the exposed lines or dashed lines in the chemical pattern. The checkerboard chemical pattern, which cannot be generated with typical self-assembled block copolymer morphologies, consists of either offset, parallel, dashed lines, or alternating lines and dashed lines, and is used in the fabrication of dynamic random access memory. The degree of perfection and domain uniformity of the assembled block copolymer thin films on the complex pattern were a function of the commensurability of the volume fraction of PS in the blend (ϕS) with the fraction of area on the pattern wet by PS (FS), as well as the volume fraction of homopolymer in the blend (ϕH). The best assembly...

Modification of a polystyrene brush layer by insertion of poly(methyl methacrylate) molecules

The ability to tune the wetting behavior of poly(styrene-block-methyl methacrylate) on a polystyrene (PS) brush by insertion of hydroxyl-terminated poly(methyl methacrylate) (PMMA-OH) was demonstrated. The brush properties before and after insertion of PMMA-OH were studied with goniometry, ellipsometry, near edge x-ray absorption fine structure spectroscopy, and scanning electron microscopy. The initial PS brush served as a barrier to the grafting of PMMA onto the substrate. The amount of PMMA that could penetrate through the PS brush barrier and graft onto the substrate depended on the initial PS brush thickness. As a result, the PS:PMMA ratio in the final composite brush, and therefore the brush wetting properties, could be carefully controlled. The final composition also depended on the grafting sequence of the brush molecules. This may offer a generalized approach for fabricating neutral brush surfaces without requiring the synthesis of specific random copolymers.

Directed Self-Assembly of Triblock Copolymer on Chemical Patterns for Sub-10-nm Nanofabrication via Solvent Annealing

Directed self-assembly (DSA) of block copolymers (BCPs) is a leading strategy to pattern at sublithographic resolution in the technology roadmap for semiconductors and is the only known solution to fabricate nanoimprint templates for the production of bit pattern media. While great progress has been made to implement block copolymer lithography with features in the range of 10-20 nm, patterning solutions below 10 nm are still not mature. Many BCP systems self-assemble at this length scale, but challenges remain in simultaneously tuning the interfacial energy atop the film to control the orientation of BCP domains, designing materials, templates, and processes for ultra-high-density DSA, and establishing a robust pattern transfer strategy. Among the various solutions to achieve domains that are perpendicular to the substrate, solvent annealing is advantageous because it is a versatile method that can be applied to a diversity of materials. Here we report a DSA process based on chemical contrast templates and solvent annealing to fabricate 8 nm features on a 16 nm pitch. To make this possible, a number of innovations were brought in concert with a common platform: (1) assembling the BCP in the phase-separated, solvated state, (2) identifying a larger process window for solvated triblock vs diblock BCPs as a function of solvent volume fraction, (3) employing templates for sub-10-nm BCP systems accessible by lithography, and (4) integrating a robust pattern transfer strategy by vapor infiltration of organometallic precursors for selective metal oxide synthesis to prepare an inorganic hard mask.

Graphoepitaxial assembly of asymmetric ternary blends of block copolymers and homopolymers

Ternary blends of cylinder-forming polystyrene-block-poly(methyl methacrylate) block copolymers and polystyrene and poly(methyl methacrylate) homopolymers were assembled in trench features of constant width. Increasing the fraction of homopolymer in the blend increased the spacing and size of block copolymer domains, which were oriented perpendicular to the substrate to form a hexagonal lattice within the trench. The number of rows of cylinders within the trench was controlled by the blend composition. Depending on the domain size and spacing, the hexagonal lattice was stretched or compressed perpendicular to the trench walls but not perturbed parallel to the walls, indicating a decoupling of the perturbation in the perpendicular and parallel directions. The row spacing was uniform across the trench as a function of position from the trench wall. The results are compared with an analytical model and with Monte Carlo simulations.

Mechanism and dynamics of block copolymer directed assembly with density multiplication on chemically patterned surfaces

In this work, we used scanning electron microscopy (SEM), in situ coherent small angle x-ray scattering (SAXS), and Monte Carlo molecular simulation to gain insights into the dynamics of block copolymer directed assembly with density multiplication on chemically patterned surfaces. During directed assembly, it was observed with SEM that poly(styrene-block-methyl methacrylate) initially formed discrete polystyrene domains that lacked long-range order at the free surface. After further annealing, the polystyrene domains gradually coalesced into linear domains that were not registered fully with the underlying chemical pattern. The linear domains could be trapped in metastable morphologies. Finally, the linear polystyrene domains formed perpendicular lamellae in full registration with the underlying chemical pattern. It was revealed with SAXS that scattering peaks characteristic of the period of the chemical pattern appeared and disappeared at the early stages of assembly. Finally, the morphological evolutio...

Exploring the manufacturability of using block copolymers as resist materials in conjunction with advanced lithographic tools

The authors discuss studies of the capabilities and advantages of using self-assembling block copolymers in the lithographic process. Directing the assembly of these materials on lithographically defined chemically nanopatterned surfaces offers the potential to improve the dimensional control of features at the nanoscale while retaining essential attributes of the lithographic process, such as registration, patterning of regular fabric architectures, and a high degree of pattern perfection.

Shape control and density multiplication of cylinder-forming ternary block copolymer-homopolymer blend thin films on chemical patterns

The effect of the chemical pattern spot size, the spacing on the size, and the shape of the cylindrical domains in thin films of a ternary block copolymer/homopolymer/homopolymer blend was investigated over a range of homopolymer volume fractions. Cylinder-forming ternary blends were composed of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), and the corresponding PS and PMMA homopolymers were directed to assemble on chemical patterns that had density multiplication ratios ranging from 1:1 to 4:1. By increasing the homopolymer fraction in the blends, the dimensions of the domains were expanded. When the size of the spots on the chemical pattern was not matched with the size of the domain of the blend in the bulk, the dimensions of the domains at the free surface of the assembled films differed from those at the interface with the chemical pattern.

Directed assembly of block copolymers on lithographically defined surfaces

An outline of research on the directed assembly of block copolymer films to meet the needs of advanced lithographic systems, as defined by the International Technology Roadmap for Semiconductors, is presented. These requirements include pattern perfection, control of placement of features, the ability to generate patterns corresponding to regular fabric architectures, control of feature shapes and dimensions, scaling to below 10 nm, and pattern transfer. Accomplishments toward these requirements have been achieved by self-assembly with solvent annealing and by directed assembly on topographical or chemical patterns. Looking forward, these requirements must be met simultaneously, and examples are provided that show simultaneous achievement of many of these requirements. In addition, research focusing on specific implementation opportunities, such as directed assembly in 193 nm immersion lithography, is briefly discussed.