Nanostructured low-index layers are useful as the last layers of antireflective (AR) coatings because they can broaden their spectral ranges and improve the performance for oblique light incidence. Structuring of evaporated organic layers by plasma opens a route to produce inorganic interference stacks and low-index layers in the same vacuum process. The organic material uracil has been investigated as a template material for AR nanostructures. An additional plasma-treatment step was added to the manufacturing process, which decreases the organic fraction of the coating substantially. As a result, a better environmental stability and higher transmission in the ultraviolet range was achieved.