Photolithographic masks and nano-imprint lithography masks with calcium fluoride substrates are disclosed. A photolithographic mask has a calcium fluoride substrate having a surface, a patterned layer disposed on the surface, and a polymer layer forming a pellicle that covers the patterned layer. A mask for nano-imprint lithography has a calcium fluoride substrate with a surface and a nano-imprint lithography pattern formed on the surface. Such masks can be used in a method for reducing the effects of hydration during lithography. In the method a layer of photoresist is formed on a substrate. A mask having a substrate made of calcium fluoride with a patterned surface is disposed proximate the layer of photoresist. The photoresist is exposed to radiation that passes through the mask. The radiation is characterized by a vacuum wavelength between about 190 nm and about 450 nm. Calcium fluoride masks can also be used to reduce the effects of hydration nano-imprint lithography.