The use of a cascade is recommended for optimum performance of the developer and for the highest cleanliness during immersion development. The development often takes place in only one container. Exposed resist areas are completely dissolved, remain in the developer and thus also consume the developer successively. If the developed wafers usually present in one carrier are rinsed with DI water, the solids of the contaminated developer residues may precipitate and slightly pollute the wafer surface. Even though effect can be prevented by intense rinsing with water, a cascade should be used to be on the safe side.
For this purpose, two or even three developer containers are placed in a row. In the first container, wafers are fully developed. After completion of the development, the wafers are immersed briefly in the fresh developer of the second container (5 seconds). The process can then be completed with a third bath. The subsequent rinse is carried out in DI water. Contaminations are excluded with this development regime.
If the developer is consumed in the first bath (see “Developer ageing”), it is replaced by a second container, and, if necessary, the third container is used to replace the second one. By this process, the developer is optimally exploited and the highest cleanliness is obtained.