Materials for Microlithography

Fine lithographic patterns are produced when radiation (photons, electrons, ions, or neutral particles) interacts with a material, and produces physical or chemical changes (or both) in that material selectively, as required to replicate the desired pattern. The type and energy of radiation is important to characterize the process, the amount of radiation (exposure) generally must be controlled, and the resulting removal of material by physical or chemical means must also be controlled. Photons generally interact with materials somewhat differently than electrons, which are again different than ions, as momentum of the incoming radiation increases from photon to electron to ion. The incoming radiation excites electrons in the material, and these generally produce the chemical changes "developed" by dry or wet chemical processes in many forms of lithography. The volume of material exposed by the incoming radiation depends on how it penetrates the material being exposed, how it is scattered by