Exciting tin-oxo cages: light-induced chemistry for nanopatterning
This thesis is about molecular tin-oxo cage structures, which contain a core composedof twelve tin and twenty oxygen atoms. Each tin atom is attached to a hydrocarbonchain; in this work these are butyl groups. The tin-oxo cage has a 2+ charge, whichis balanced by one or two negatively charged counterions.A thin film of these tin-oxo cages can be used as a photoresist. This is a photo-sensitive film that changes solubility upon light exposure. A positive-tone photoresistbecomes more soluble in a solvent or mixture of solvents (called developer) when itis illuminated, while a negative-tone photoresist becomes less soluble. By exposing aphotoresist to a light pattern, a pattern can be written in the photoresist.It is known that light absorption on tin-oxo cages leads to photochemical reactionsin which the hydrocarbon (butyl) chains are cleaved and removed. The tin-oxo cagesthen bind to each other and form an insoluble network as the end product. Thetin-oxo cage material therefore belongs to the negative-tone photoresist class. Betterunderstanding of the photoreactions of tin-oxo cages is the main goal of the researchdescribed in this thesis.Tin-oxo cages are of special interest because they contain a large number of tinatoms, while also being soluble in organic solvents. This makes them possibly applica-ble as photoresists for Extreme Ultraviolet (EUV) light, with a patterning wavelengthof 13.5 nanometers. As a result of the ultra-short wavelength, EUV light can be usedto pattern on an even smaller scale (higherresolution). However, EUV light is ex-pensive to produce, which means that it is important to use this light efficiently. Tinatoms are good absorbers of EUV light; tin-containing materials could therefore needless EUV light to change solubility (highersensitivity).