Huiman Kang

Directed Self-Assembly of Block Copolymers for Nanolithography: Fabrication of Isolated Features and Essential Integrated Circuit Geometries

Self-assembling block copolymers are of interest for nanomanufacturing due to the ability to realize sub-100 nm dimensions, thermodynamic control over the size and uniformity and density of features, and inexpensive processing. The insertion point of these materials in the production of integrated circuits, however, is often conceptualized in the short term for niche applications using the dense periodic arrays of spots or lines that characterize bulk block copolymer morphologies, or in the long term for device layouts completely redesigned into periodic arrays. Here we show that the domain structure of block copolymers in thin films can be directed to assemble into nearly the complete set of essential dense and isolated patterns as currently defined by the semiconductor industry. These results suggest that block copolymer materials, with their intrinsically advantageous self-assembling properties, may be amenable for broad application in advanced lithography, including device layouts used in existing nanomanufacturing processes.

Placement Control of Nanomaterial Arrays on the Surface-Reconstructed Block Copolymer Thin Films

We present a control strategy for the facile placement of densely packed nanomaterial arrays (i.e., nanoparticles and nanorods) on surface reconstructed polystyrene-block-poly(methyl methacrylate) thin film patterns. The surface reconstruction of perpendicularly oriented block copolymer thin films, which were produced by a treatment with selective solvent vapors for both blocks, created the topographical nanopatterns with enough height contrast for nanoparticle deposition without the need for additional selective etching of a single block domain. The deposition method of nanomaterials was also optimized, and densely packed one- and two-dimensional nanomaterials arrays in the grooves of the block copolymer film patterns were fabricated efficiently. Then, we demonstrated that height contrast of the surface reconstructed block copolymer films could be reversed by electron beam irradiation resulting in nanomaterial arrays placed at the mesa phase of the nanopatterns. On the basis of this nanomaterial placement control strategy, dual nanomaterial arrays on a single block copolymer pattern were also realized.

Graphoepitaxial assembly of symmetric block copolymers on weakly preferential substrates.

www.MaterialsViews.com C O M M U Graphoepitaxial Assembly of Symmetric Block Copolymers on Weakly Preferential Substrates N IC A By Eungnak Han , Huiman Kang , Chi-Chun Liu , Paul F. Nealey , and Padma Gopalan * IO N Self-assembly of block copolymers (BCPs) has emerged as a simple and robust “bottom-up” method for fabricating dense and periodic nanostructures as they microphase separate into nanoscale domains. [ 1–5 ] In general, microphase separation of BCPs in thin fi lms on unpatterned surfaces leads to the formation of randomly oriented grains. This low degree of lateral ordering in thin fi lms has led to the use of chemically [ 6–10 ]

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...

Control of the critical dimensions and line edge roughness with pre-organized block copolymer pixelated photoresists

Sphere-forming polystyrene-block-poly(t-butyl acrylate) (PS-b-PtBA) diblock copolymer with catalytic amounts of photo-acid generator (PAG) formulated a pixelated photoresist. In thin films with single-sphere thickness, hexagonal arrays of spheres (∼20 nm diameter on a 40 nm pitch) of PS within a matrix of PAG segregated in PtBA was obtained through solvent annealing. Upon exposure and post-exposure baking, the soluble PtBA matrix was converted to insoluble poly(acrylic acid), such that a negative pattern could be formed in the chlorobenzene developer. The concept of pixelation was demonstrated by exposing line and space patterns with increasing widths. In contrast to the width of the exposure fields that increased monotonically, the widths of the pixelated resist structures after development were quantized with respect to an integer number of rows of spheres. Furthermore, line edge roughness could be correlated with the size of each pixel (diameter of spherical domain).

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.