Carbon-based dielectric materials for semiconductor structure fabrication, and the resulting structures, are described. In an example, method of patterning a layer for a semiconductor structure includes forming a plurality of trenches in a dielectric layer above a semiconductor layer above a substrate to form a patterned dielectric layer. The method also includes filling the plurality of trenches with an adamantane-based carbon hardmask material. The method also includes removing the patterned dielectric layer selective to the adamantane-based carbon hardmask material. The method also includes using the adamantane-based carbon hardmask material to pattern the semiconductor layer.