High-resolution guiding patterns for the directed self-assembly of block copolymers

Abstract

The presented thesis entitled “High-resolution guiding patterns for the directed self-assembly of block copolymers” investigates strategies to introduce long-range order into block copolymer thin films for nanopatterning applications. Structures defined by top-down lithography that enable the introduction of long-range order into an otherwise disordered thin film of block copolymers are referred to as guiding patterns. This thesis explores and develops different techniques that enable the fabrication of guiding patterns with a particular focus on methods capable of providing high-resolution and high-accuracy, because they are at the prospect of playing a crucial role in the directed self-assembly of very low-pitch block copolymer materials. We demonstrate the directed self-assembly of an 11.7 nm full-pitch PS-b-PMMA block copolymer with guiding patterns fabricated by means of five different top-down lithography techniques. One strategy to fabricate guiding patterns consists in the generation of topographic structures, which is referred to as graphoepitaxy. In this case, we have used extreme-ultraviolet interference lithography to fabricate trenches with nanometer precision to study the self-assembly behavior of block copolymers under nanoconfinement with high accuracy. This system has allowed us to develop a free energy model to predict for which guiding pattern dimensions the defect-free directed self-assembly can be expected. Moreover, we have used electron beam lithography for the fabrication of sub-10 nm wide topographical guiding patterns and study the directed self-assembly of block copolymers in structures with feature sizes close to the material’s half-pitch. Another strategy to fabricate guiding pattern consists of chemical surface modification to create areas that are selectively affine to one of the blocks. We have presented a novel approach based on thermal scanning probe lithography and adjust the patterning conditions for the fabrication of chemical guiding patterns with 10 nm line width. Due to the absence of the proximity and diffraction effects, thermal scanning probe lithography is ideal for the fabrication of dense high-resolution chemical patterns. As a third strategy to align block copolymers, we use grain boundaries in block copolymer thin films as order-inducing surfaces. A surface modification is used to trap a grain of vertically oriented block copolymers between two grains of horizontally oriented block copolymer domains in a controlled manner. We call the developed technique “grain-boundary induced alignment”. To demonstrate its working principle we employ mechanical AFM and electron beam direct writing, and show the ordering of block copolymers on length scales of various hundreds of nanometers. The presented thesis is complemented with the development of a probe-based imaging technique to study the thermal conductivity of polymer materials with sub-10 nm lateral resolution. The dissipation of heat into a sample is determined at each measurement point by means of an electrical circuit that is integrated into the cantilever. We study the thermal conductivity of PS-b-PMMA block copolymers with different pitches and different orientations. This technique represents an advance in the investigation of polymeric surfaces due to its high resolution and good material sensitivity.