Simple solutions of NaOH, or KOH could also be used, but because of the possibility of mobile ion contamination in MOS devices, metal ion free developers are often used. These are usually TMAH, tetra-methyl ammonium hydroxide. Some developers also contain surfactants to improve wetting properties. Each developer used has a different dilution, and some require longer development times than others. Developers are generally matched to a type of photo resist. Though they may be interchangeable to some extent, changing the type of developer used in a process will usually change the exposure time necessary to resolve the pattern. Plasma etching with oxygen (Ashing) is also effective for removing organic polymer debris.

Hard bake:

Hard bake is carried out ~110-150°C to stabilize and harden the developed photo resist. This hardening of PR is required for the subsequent aggressive processes such as Ion implantation or Plasma etching. This bake removes the remaining solvent and traces of developing solution. As a result the possible solvent burst effects during the subsequent vacuum processing are eliminated. Post bake introduces some stress in the resist and it may slightly reduce the resist thickness also. With sufficient time and/or temperature, the resist will undergo plastic flow. Longer or hotter post bake makes the resist removal harder. In some processes like metal lift-off patterning, where soft photo resist is used the hard bake is not needed.