Chemorheology of Sol-Gel Silica for the Patterning of High Aspect Ratio Structures by Nanoimprint

Among the existing methods, nanoimprint lithography (NIL) emerges as a simple route for surface patterning at the submicrometer scale over large areas. Thanks to their tunable properties, sot gel materials form an alternative class of resist for NIL. However, there is only little understanding of the rheological properties responsible for their good imprint ability. On the basis of previous works on thermal curing of thermosets, this article establishes a framework which can be used to tune the imprint conditions and to apprehend the rheological properties of complex hybrids materials. Using a combination of dynamic mechanical analysis (DMA) and scratch tests, we were able to model the thermorheological behavior of methyltriethoxysilane (MTES) gel films during isothermal treatments in a time temperature-transformations (TTT) diagram. Infrared spectroscopy study of the gel demonstrates the existence, for the same elaboration chemistry, of a condensation threshold independent of the temperature above which the material vitrifies: this reveals the closed relationship between the rheology and the chemical microstructure of the gel. We also discussed the strong influence of the elaboration chemistry on initial microstructure and therefore on vitrification.