Abstract
The integration of block copolymer (BCP) self-assembled nanopattern formation as an alternative lithographic tool for nanoelectronic device fabrication faces a number of challenges such as defect densities, feature size, pattern transfer, etc. Key barriers are the nanopattern process times and pattern formation on current substrate stack layers such as hard masks (e.g., silicon nitride, Si3N4). We report a rapid microwave assisted solvothermal (in toluene environments) self-assembly and directed self-assembly of a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) BCP thin films on planar and topographically patterned Si3N4 substrates. Hexagonally arranged, cylindrical structures were obtained and good pattern ordering was achieved. Factors affecting BCP self-assembly, notably anneal time and temperature, were studied and seen to have significant effects. Graphoepitaxy within the topographical structures provided long range, translational alignment of the patterns. The effect of surface topography feature size and spacing was investigated. The solvothermal microwave based technique used to provide periodic order in the BCP patterns showed significant promise and ordering was achieved in much shorter periods than more conventional thermal and solvent annealing methods. The implications of the work in terms of manufacturing technologies are discussed.
Highlights
Block copolymer (BCP) lithography [1] is a “bottom-up” process relying on microphase separation of BCP thin films [2,3,4] to form highly ordered block arrangements as a nanopattern and offers promise for the fabrication of sub-10 nm feature sizes
Graphoepitaxial methods for the directed self-assembly of the BCP proved successful with excellent alignment of the PDMS cylinders observed
The topography used here was consistent with production of low defect densities and further that the variation in channel width controls the number of cylinders within a channel
Summary
Block copolymer (BCP) lithography [1] is a “bottom-up” process relying on microphase separation of BCP thin films [2,3,4] to form highly ordered block arrangements as a nanopattern and offers promise for the fabrication of sub-10 nm feature sizes. Two issues of key interest are the time taken to induce long range order in the BCP thin films and substrate surfaces (other than simple silicon termination) which are routinely used in conventional UV-photolithography Hard masks such as silicon nitride (Si3N4) are used in substrate stacks that allow pattern transfer from low-dimension, thin polymer patterns to the substrate with high fidelity and aspect ratio [7,8,9]. We apply the use of the emerging microwave assisted solvothermal method (work in this area is in its infancy compared to more established methods of inducing self-assembly [2,3,4]) to promote self-assembly of a polystyrene-blockpolydimethylsiloxane (PS-b-PDMS) BCP at Si3N4 substrates and demonstrate the usefulness of this approach This BCP has particular relevance because of its high Flory-Huggins parameter (χ) [12]. Which allows sub-10 nm feature size scaling [13,14,15,16], whilst high etch selectivity between PS and PDMS [17] facilitates selective removal of PS to form topographical silica-like patterns [3,4,18,19,20]
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