Registration: Can you repeatability align one layer to another and is ~1/3 of resolution.

Throughput : Can these be done in a cost effective time. (50-100 wafers an hour, down to 1 chip per hour).

Photoresists generally consist of 3 parts; the resin, the solvent and photoactive component. The Resin is a "plastic like" or "glue-like" compound that is solid in it is undiluted state. The solvent is for dissolving the resin, allowing the resin to be applied in a liquid state. The Photoactive Compound (PAC) acts to inhibit or promote the dissolution of the resin in the developer. PAC inhibits dissolution in positive resists before light exposure. After exposure the PAC promotes dissolution of the resin.

Positive Photo Resists are most commonly used in the IC industry and they are superior to Negative Photo Resists because they do not swell during development, they are capable of finer resolution and reasonably resistant to plasma processing operations. The negative photo resist has high sensitivity but low contrast; it adheres well to substrate and has good mechanical properties and resistance to chemicals and plasma etching. Since the negative resist swells during the development, the minimum feature size is limited to 2um. NPR is difficult to remove and its developers are usually less eco-friendly organic solvents.