Fabrication and characterization of novel nanostructures based on block copolymer lithography

Abstract

Microphase-separation of block copolymers into periodic nanoscale structures has drawn considerable attention as a method for pattern generation in nanolithography. One of the main challenges is to create complex nanostructures other than closed-packed nanodots or nanoholes with hexagonal symmetry, or parallel nanolines based on block copolymer lithography. In this thesis, we demonstrate two approaches to generate novel structures such as ellipsoids, rings or square array of dots: diblock copolymers templating and triblock terpolymers. Without templating, diblock copolymer can only form spheres, cylinders, or lamellae typically. Triblock terpolymers, on the other hand, can form a larger number of morphologies even without using any template. The use of triblock terpolymers allows the formation of more complex pattern geometries compared to their diblock counterparts. Moreover, since most features in this thesis are made from an organometallic block, they have a high etch contrast and etch resistance compared to triblock terpolymers in which all three blocks contains organic segments, making them useful for pattern transfer. Rings are useful in the magnetic applications, quantum devices, and biosensors. Square symmetry array, which is not found in diblock copolymers, has applications in via formation, magnetic patterned media, and other applications. Besides, we examine the magnetic behavior of the antidot arrays of Co and pseudo-spin-valve structures with periodicity of 26 nm and 40 nm.

(cont.) As the inter-hole spacing is decreased, both experiment and simulation results show that the coercivity and switching field distribution is reduced, unlike the behavior seen in films with micron- sized holes. In the multilayer, unlike the continuous film, the NiFe reverses at positive fields due to the strong magnetostatic interactions between the Co and NiFe layers present near the holes. Finally, arrays of high-aspect-ratio single crystal silicon nanowires (SiNWs) have also been fabricate by combining block copolymer lithography and metal assisted etching. These SiNWs may be useful in the application of field-effect biosensors and lithium batteries.