Direct patterning of oxides: From nanoimprint lithography to self-assembly of block copolymers

Abstract

Oxides are a very important class of materials and their nanostructures have potential for widespread applications. As the dimensions of devices shrink, their fabrication process becomes challenging particularly when sub-100 nm feature sizes over large area are desired. Nanoimprint Lithography (NIL) and self-assembly of block copolymers are two potential candidates for next generation nanolithography. Currently, direct patterning of oxides using NIL is performed using either the sol?gel or methacrylate route. The sol-gel method offers resists with long shelf life, but with high surface energy and contains considerable amount of solvent that affects the quality of imprinting. On the other hand, the methacrylate route, limited to certain oxides, produces polymerizable resists with low surface energy, but suffers from shorter shelf life of precursors. By combining the benignant elements of both these routes, a universal method of direct thermal and UV NIL of oxides using precursors produced by reacting an alkoxide with a polymerizable chelating agent such as 2-(methacryloyloxy)ethyl acetoacetate (MAEAA) is demonstrated. MAEAA possesses ?-ketoester and methacrylate groups ? the former results in the formation of environmentally stable, chelated alkoxide with longer shelf-life whilst the latter provides a reactive methacrylate group for in situ copolymerization with a cross-linker during imprinting. Polymerization leads to trapping of cations, lowering of surface energy, strengthening of imprints, enabling easy and clean demolding over large patterned area with ~100% yield. Heat-treatment of imprints gave amorphous/crystalline oxide patterns. This method synergistically utilizes the advantages of the sol-gel and methacrylate routes and at the same time mitigates the disadvantages associated with these methods. This symbiotic alliance between the two diverse routes has enabled the demonstration of successful imprinting of numerous oxides such as Al2O3, Ga2O3, In2O3, Y2O3, B2O3, TiO2, SnO2, ZrO2, GeO2, HfO2, Nb2O5, Ta2O5, V2O5, and WO3. Moreover, this large area direct patterning simplifies steps involved in patterning of oxides, making it a prospective technique for industrial applications.

Self-assembly of block copolymer (BCP) thin films produces array of microdomains with limited long-range order that limit their application for nanolithography. Here, by combining thermal and solvent vapor annealing processes for BCP self-assembly a method called thermo-solvent annealing is introduced to improve the long-range order for a given processing time. Well-ordered microdomains of oxidized-PDMS or SiOx were produced with order better than thermal or solvent annealing alone.