Graphoepitaxy of Self-Assembled Block Copolymers on Two-Dimensional Periodic Patterned Templates

Abstract

Self-assembling materials are the building blocks of bottom-up nanofabrication processes, but they need to be templated to impose long-range order and eliminate defects. In this work, the self-assembly of a thin film of a spherical-morphology block copolymer is templated using an array of nanoscale topographical elements that act as surrogates for the minority domains of the block copolymer. The orientation and periodicity of the resulting array of spherical microdomains are governed by the commensurability between the block copolymer period and the template period and is accurately described by a free-energy model. This method, which forms high-spatial-frequency arrays using a lower-spatial-frequency template, will be useful in nanolithography applications such as the formation of high-density microelectronic structures.

A Path to Ultranarrow Patterns Using Self-Assembled Lithography

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Templated self-assembly of block copolymer thin films can generate periodic arrays of microdomains within a sparse template, or complex patterns using 1:1 templates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . However, arbitrary pattern generation directed by sparse templates remains elusive.

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“…Figure 1a schematically illustrates the templating process. A rectangular array of posts with heights of $35 nm and diameters of $10 nm was fabricated on the substrate by means of EBL exposure of hydrogen silsesquioxane (HSQ) resist 3,28 . The HSQ posts and native oxide on the silicon wafers were chemically functionalized with a brush layer of PDMS to ensure that the posts had an affinity for the PDMS block of the block copolymer and to improve annealing kinetics.…”

“…As a result, both chemical and topographical substrate features have been used to template or guide block copolymer self-assembly, imposing long-range order and generating microdomain geometries not observed in untemplated films [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] . These templates are often defined using electronbeam lithography (EBL) [3][4][5]7,8,11 , because of its ability to pattern small features of arbitrary geometry. However, the serial nature of EBL makes it clearly advantageous to minimize the density of the EBL-written features required to template a given arrangement of block copolymer microdomains.…”

“…Most work on the templated self-assembly of block copolymers for nanolithography has focused on the generation of periodic patterns of parallel lines, close-packed dots or concentric rings, using shallow trenches 1,6,9,10,[12][13][14]22,24,26 , sparse post arrays 3 or chemical templates with a periodicity either similar to that of the BCP 2,7,8,15 or a factor two, three or four times larger [3][4][5] . Nealey and colleagues have shown that non-regular features such as lamellae with bends 2,11 or square-packed dots 15 could be formed using a chemical pattern of the same density as the desired block copolymer pattern.…”

“…The HSQ posts and native oxide on the silicon wafers were chemically functionalized with a brush layer of PDMS to ensure that the posts had an affinity for the PDMS block of the block copolymer and to improve annealing kinetics. Thin PDMS layers formed at the air and substrate interfaces 3,[25][26][27] .…”