3.6 Lithography

Fabrication of devices depends on selective processes such as removal of material (etching) addition of material (deposition) and modification of material (implantation, diffusion, etc.). One need to have defined areas on the substrate exposed to these processes and the rest of the substrate must be protected also during the same processes. These selected/unselected areas make up the pattern. Pattern definition takes place in the resist which is a thin layer of polymeric material coated on the substrate. The resist is modified so that it remains in some areas and is removed in others. Lithography in the integrated circuit technology context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light.