Templated Self-Assembly Of Block Copolymers And Nanoparticles

In modern semiconductor industries, the conventional optical lithography method gradually approaches its dimensional limitation for device design due to the restric-tion of wavelength of light. Further extension of the size of the feature structures to smaller dimensions for higher resolution becomes difficult and costly. Block copoly-mer lithography, which combines the conventional "top-down" lithography method and "bottom-up" block copolymer self-assembly procedure, has been proven to be a sim-ple and low-cost process to overcome the dimension limitation of traditional lithogra-phy method without changing the current semiconductor manufacturing process. This lithography method transfers the patterns formed by block copolymer microdomains (in the range of 5-50nm) into the functional materials through a series of continuous processes. The pattern obtained from block copolymer microdomains often requires order on large length scales as well as local small areas in practical applications. In this case, patterned template directed self-assembly of block copolymers becomes ex-tremely important and has attracted much attention in recent experiments. This disser-tation mainly focuses on the directed self-assembly behavior of block copolymers on distinct patterned templates by using the self-consistent field theory of block copoly-mers and gives some guidelines for the practical device design. We also study the block copolymer templates directed self-assembly of rod-shaped nanoparticles, and system-atically investigate the influence of aspect ratio of rod particles on the phase behavior of the hybrid system.In chapter 1, we give a brief introduction of polymers and nanoparticles. Phase be-havior of diblock copolymers in experiments and theories is provided in detail. Recent progress of template directed self-assembly of block copolymers and its application in semiconductor fields are emphasized in the following part. We also outline the recent progress of polymer/nanoparticle composite in experiments and theories, and present some recent progress on the synthesis of complex geometrical nanoparticles.In chapter 2, we mainly introduce the theoretical tools used in our dissertation. First we detail the Gaussian chain model of flexible polymer chains. Then the self-consistent field theory of diblock copolymers are provided in detail and the self-consistent field equations are derived by minimizing the free energy of diblock copoly-mers with block concentrations and the corresponding fields. By numerically solving these self-consistent field equations, we could obtain the equilibrium morphologies of diblock copolymers. Pseudo-spectral algorithm to solve the diffusion equation of di-block copolymer chain is also detailed. At last, we briefly outline the hybrid particle field theory which could explicitly consider the coordinate, size and shape of particles within copolymer templates.In chapter 3, we study a two-dimensional sparse hexagonal lattice template directed self-assembly behavior of block copolymers by using the self-consistent field theory. Our theoretical morphologies of block copolymers are consistent with recent experi-mental SEM images. Furthermore we study the square lattice template to direct the ordered block copolymer microdomains. Block copolymers form single square struc-ture or nested squares in the presence of square lattice template. The influence of posts' size and shape on the final block copolymer morphologies is also considered. Finally, some complex templates with combined lattices are designed to direct the self-assembly morphologies of block copolymers and the results reveal that these complex sparse lat-tice templates could induce the nano-structures of block copolymers with controlled order on both large areas and local small areas simultaneously.In chapter 4, we present a two-dimensional sparse rectangle lattice template to direct the equilibrium morphologies of block copolymers. The areal density of sub-strate is multiplied by a factor of 34 through the self-assembled block copolymer mi-crodomains without losing the long-range order. Local spacings of the block copoly-mer microdomains and their orientation can be modulated by template spacings. The selection of optimal templates for specific applications is summarized in the phase dia-gram based on the template spacings along x and y directions. The suggested approach provides a candidate to enhance the performance of current semiconductor devices, especially the ultrahigh-density data storage media.In chapter 5, we investigate the self-assembly behavior of AB diblock copolymers on a concentric circle template. The block copolymers form perfect ring structures within the template. The number of ring structures between two circle walls is relevant with the outer and inner radiuses of concentric circles. We present the phase diagram of ring structures by varying the radiuses of inner and outer circles. Results show that the number of perfect ring structures increases with the small inner radius in a limited range. Based on the phase diagram, we design a template constructed by two curved walls and two straight double lines together, and the block copolymers form a curved dot-line structures and the line holds the shape of curved template perfectly. The pro-cedures outlined here provide a platform to stimulate further studies on designing com-plex geometries of block copolymers for its applications in the modern semiconductor devices, especially for the integrated circuit layouts.Finally, our attention is focused on the self-assembly of rod-shaped particles into nanometer-length-scale structures within AB diblock copolymer templates. The the-oretical results obtained from the extended hybrid particle field methods can account well for a series of recent experimental findings. Furthermore, we construct the phase diagrams of the mixture with different aspect ratios of particles by changing the par-ticle concentration and the volume fraction of A block. The variation of the aspect ratio in different particle concentrations will significantly influence the effective vol-ume of A component and consequent phase behavior of nanoparticle/copolymer hybrid systems, which may account for the emergence of some unexpected phenomena of morphological transitions. The present study provides insightful guidance to control the nanometer-length-scale structures of shaped particles for potential applications as functional devices.