text: Photolithography and X-ray lithography have been used to etch substrates, often silicon. A resist, or photosensitive material, is coated onto a substrate. A mask is applied above the resist that often consists of gold or other compounds that absorb X-rays. The region exposed to light either becomes soluble in a photoresist developer (e.g. radical species) or insoluble in a photoresist developer (e.g. crosslinked species), ultimately resulting in a patterned surface. X-ray sources are beneficial over UV-visible light sources as the shorter wavelengths enable production of smaller features.