Effects of Silica Sources on Nanoporous Organosilicate Films Templated with Tetraalkylammonium Cations
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Effects of Silica Sources on Nanoporous Organosilicate Films Templated with Tetraalkylammonium Cations Salvador Eslava,12+ Jone Urrutia,1 Abheesh N. Busawon,3 Mikhail R. Baklanov,1 Francesca Iacopi,2 Karen Maex,4 Christine E. A. Kirschhock,2 and Johan A. Martens2 1
IMEC, Kapeldreef 75, 3001 Leuven, Belgium. 2Centrum voor Oppervlaktechemie en Katalyse, Katholieke Universiteit Leuven, Kasteelpark Arenberg 23, 3001 Leuven, Belgium. 3Imperial College London, London, SW7 2AZ, UK. 4Department of Electrical Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 10, 3001 Leuven, Belgium.+SE’s current address: Chemistry Dept., Univ. of Cambridge, Lensfield Road CB2 1EW, UK ([email protected]). ABSTRACT Nanoporous organosilicate films have been recently prepared using tetraalkylammonium cations in acid and basic media, outperforming other materials. Resulting films using basic medium were called zeolite-inspired low-k dielectrics. Here we study the dependence of the properties of these films on the used silica sources: methyltrimethoxy silane (MTMS) and tetraethyl orthosilicate (TEOS). A set of experiments varying the MTMS:TEOS ratio were prepared in acid medium and characterized. A textural, physico-chemical, mechanical, and electrical characterization of this series of experiments is presented. INTRODUCTION Applications of nanoporous organosilicates include different fields such as lasers, biotechnology, molecular separations, and low-k dielectrics in integrated circuits.[1] For some of these applications, film deposition is required. The pore network and the matrix composition are crucially important for the final film properties.[2] To obtain a porous network, several studies have been carried out involving the use of sacrificial molecules called porogens.[1-4] Recently, we have shown that tetraalkylammonium bromides (TAABr) of different alkyl chain length outperform other porogen molecules in terms of porosity results.[5] This was demonstrated by using TAABr molecules as porogens in the spin coating of organosilicate sols prepared from an equimolar quantity of tetraethyl orthosilicate (TEOS) and methyltrimethoxysilane (MTMS) in acid conditions. The alkyl chain length of the TAABr and the porogen concentration defined the final pore network. Other properties such as hydrophobicity, elastic modulus, and dielectric constant were shown to be dependent on the pore network nanocasted by the TAABr molecules. Alternatively, organosilicate films could also be prepared in basic conditions using aqueous tetraalkylammonium hydroxides (TAAOH), giving rise to zeolite-inspired low-k (ZLK) dielectrics.[6] The comparison of obtained films with other materials such as spin-on zeolite films evidenced the advantages of these approaches.[5,6] In this work, we contribute to the study on the organosilicate films nanocasted with TAABr porogens. We study the dependence of the final film properties on the proportion of MTMS relative to TEOS. A series of experiments varying the MTMS:TEOS ratio and keeping rest of variables w
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