Photolithography and X-ray lithography have been used to etch substrates, often silicon. The materials employed in multiphoton lithography are those normally used in conventional photolithography techniques. Electron beam lithography has the disadvantage of being much slower than photolithography. In some cases, the masking material is a photoresist which has been patterned using photolithography. An alternative to photolithography is nanoimprint lithography. The stamp is produced from the normal techniques of photolithography or electron-beam lithography. Photolithography and etching removes some polymer layers to uncover conductive pads on the ICs. Other processes are called photomasks and photolithography. Rockwell Science Center also developed refractive microlens technology, including gray scale photolithography. The argon fluoride laser is important in photolithography of silicon chips. They are created via photolithography or photochemical machining. These wafers are then polished to a mirror finish before going through photolithography. Luminescent provided sophisticated mathematical optimization for use in photolithography masks. Integrated circuits are made using photolithography, i.e. exposure to light. Micropatterning techniques, such as photolithography and inkjet printing belong to this category.