Photoresists (also photo coatings) are primarily used in micro electronics and micro system technologies for the production of µm- and sub-µm structures. These resists are generally deposited by spin coating in a range between 250
Photoresists are light-sensitive, they are affected by light exposure and high temperatures, and age-related changes occur during storage. Resists are therefore filled in light-protected amber glass bottles,
During storage, red azo dyes develop due to a thermal chemical reaction of the light-sensitive component with the novolak, causing a darkening of the resist. Even small amounts of the dye lead to darkening,
If new and clean substrates (wafers) are used, a bake at approximately 200 °C for several minutes is sufficient for drying, but the substrates have to be processed quickly afterwards.
Adhesion between coating and substrates is a very sensitive feature. Smallest changes of the cleaning procedures or the process parameters can have a fatal impact on the adhesive strength.
Prior to the coating procedure, resists have to be adjusted to the temperature of the (preferably air-conditioned) working area. If the resist is too cold, air moisture may precipitate on the resist.
Bubbles after spin deposition are in most cases air bubbles, e.g. if the resist bottle was agitated or moved around, or if the resist was diluted prior to the coating step. Coating procedures performed immediately after bottle opening,
Just recently coated resist films still contain a substantial amount of residual solvent, depending on the respective film thickness. The subsequent bake step at 90 – 100 °C is performed in order to dry the resist films,
The exposure is performed using masks in suitable exposure systems such as e.g. steppers (i-, g-line), mask aligners or contact exposure systems in the appropriate spectral working range.
During development, a positive tone resist film is structured by a removal of exposed areas, while unexposed areas are removed when negative resists are used. To achieve reproducible results,