ABSTRACT
Photolithography is the photographic technique to transfer replica of a master pattern into a substrate of a different material. High etch resistance is an essential parameter for effective pattern transfer. Etch resistance of a photoresist (PR) depends on the ratio of the unsaturated atomic components of the PR polymer structures; this unsaturation offers the optimal level of etch resistance. In negative PRs, the monomers undergo cross-linking and polymerize upon exposure to light, and the exposed parts become insoluble in the developer, usually in an organic solvent. Both positive and negative resists are used in microfabrication process depending on the requirement. A mask for optical lithography consists of a transparent plate called blank, covered with a patterned film of opaque material. In a latest optical-mask-making process, a computer tape is used to drive an optical pen that directly writes the pattern on the reticle mask. Computer-generated patterns are used as very large scale integration masks.
