MESOSCALE MODELING OF DIRECTED SELF-ASSEMBLIES OF BLOCK COPOLYMERS FOR NANOLITHOGRAPHY
Pinge, Shubham Dattaram
Over the past decade, with the ever-increasing demand for miniaturization of micro-electronic devices, directed self-assembly (DSA) of block copolymers (BCPs) has attracted the interest of both academia and industry as a promising ‘bottom-up’ technique to develop defect free nanolithographic patterns. DSA is not restricted by inherent diffraction-based limitations of conventional photo-lithography and has a much lower cost of ownership compared to the competing alternatives. Two of the most prominent DSA techniques used to orient BCPs include graphoepitaxy which uses surface topography to direct the BCPs and chemoepitaxy, that employs enthalpic interactions of a patterned substrate to form ordered structures out of thin films. This work first explores graphoepitxial BCP self-assembly to form ordered cubically packed cylindrical arrays using topographical pillars. Using a coarse-grained molecular dynamics (CGMD) framework, simulations are carried out on an asymmetric BCP confined between two flat plates at two different plate dimensions: least confinement and highest confinement. The least and highest radial separation between adjacent pillars are kept the same as the flat plate separations. A direct correlation was observed in the number of continuous micro-domains of the maximum and minimum confinement dimensions in the pillars template with the least and highest flat plate separations trials. With the optimum chain length employed, the surfaces with affinity to the minor phase can direct the BCP self-assembly to form ordered arrays of minor phase cylinders. Design plots were thus generated at various BCP volume fractions to find the optimum BCP molecular weights. Secondly, we study chemoepitaxial DSA with Liu-Nealey flow to form lamellae patterns with symmetric BCPs with a CGMD framework. Defect-free lamellae are formed for the two substrate geometries after which the system is quenched below the glass transition. The defect free lamellae are then etched using either a wet or a dry etching schematic. Depending on the type of etching, parameters like solvent type (wet) or selectivity (dry) are studied for their effect on resist morphology. Subsequently, a three-dimensional edge detection is performed on the resist domains (PS) to evaluate the edge roughness on three process stages: anneal, pre-etch and post-dry/wet etch. The simulations results are also compared with top view and cross-sectional SEM images. Efforts to mitigate roughness and defectivity by employing additives, using BCP blends of different molecular weights or replacing a fraction of the BCPs with equivalent homopolymers is also studied. Some commons defects and their possible annihilation using suitable dry-etches is then discussed. Lastly, efforts to model the materials and processes for the next-generation lithographic techniques is studied. These include preliminary results for oligomers for self-assembled monolayer nanopatterns and chemically amplified resists for extreme ultraviolet lithography.
Nanotechnology; Chemical engineering; Block-Copolymers; Directed-Self Assembly; Lithography
Joo, Yong L.
Wiesner, Ulrich B.; Daniel, Susan
Ph.D., Chemical Engineering
Doctor of Philosophy
Attribution-NonCommercial-ShareAlike 2.0 Generic
dissertation or thesis
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