Self-Assembly of Block Copolymers by Solvent Vapor Annealing, Mechanism and Lithographic Applications

SELF-ASSEMBLY OF BLOCK COPOLYMERS BYSOLVENT VAPOR ANNEALING, MECHANISM ANDLITHOGRAPHIC APPLICATIONS FEBRUARY 2014XIAODAN GUB.S., NANJING UNIVERSITYM.S., UNIVERSITY OF MASSACHUSETTS AMHERSTPh.D., UNIVERSITY OF MASSACHUSETTS AMHERSTDirected by: Professor THOMAS P. RUSSELL Block copolymers (BCP) are a unique class of polymers, which can self-assembleinto ordered microdomains with sizes from 3 nm to about 50 nm making BCPs anappealing meso-scale material. In thin films, arrays of BCP microdomains with long-range lateral order can serve as ideal templates or scaffolds for patterning nano-scalefunctional materials and synthesizing nanostructured materials with size scales that exceed the reach of photolithography. Among many annealing methods, solvent vapor annealing (SVA) is a low-cost, highly efficient way to annihilate defects in BCP thinfilms and facilitates the formation of highly ordered microdomains within minutes.Directing the self-assembly of BCPs could, in principle, lead to the formation of domains with near perfect lateral ordering. The mechanism of SVA of BCPs, however, is still ill-understood, albeit it has been widely adopted in research laboratories around the world for the past decade.In the first part of this thesis, the ordering process of BCP thin films duringannealing in neutral solvents was investigated mainly by in situ synchrotron X-rayscattering. Briefly, the solvent molecules impart mobility to the BCP and enable amarked improvement in the lateral ordering of the BCP microdomains. Both, BCPconcentration in the swollen film and the rate of solvent removal play a key role inobtaining films with well-ordered microdomains. The amount of swelling in a BCP thinfilm during SVA depends on the chemical nature of the blocks, the quality of the solvent,and the molecular weight of the BCP. A high degree of swelling still low enough toprevent solvent-induced mixing (disordering) of BCP microdomains,provides a highchain mobility, and thus results in the formation of arrays of ordered microdomains withlarge grain sizes after SVA in neutral solvents.The rate of solvent removal is another critical parameter for obtaining long-rangelateral order in BCP thin films after SVA in neutral solvents. While in the swollen stateordered structures form with exceptional order, removal of the solvent results in adeterioration of order due to the confinement imposed to a BCP in a thin film by the rigidsilicon substrate. It was found, however, that an instantaneous solvent removal can minimize disordering to preserve the order formed in the swollen state. Self-assembled BCP microdomains also serve as ideal template to pattern othermaterials with exceptional lateral resolution. In this thesis, two examples of BCPlithography was also demonstrated. A reconstruction process was used to enhance the etch contrast between two organic blocks. In one example, a BCP pattern was transferredto a silicon substrate to form high aspect ratio, 5:1, sub-10nm silicon lines or holes with high fidelity. While in a second example, I demonstrated the fabrication of silicon oxidedots with an areal density as high as 2 Tera dots per inch by BCP templates, which hasthe potential to serve as etch mask for bit pattern media applications.