6. Which developers are optimal for e-beam resists, and how do factors like developer concentration and temperature influence the result?
During development, a positive tone resist film is patterned by a removal of exposed areas, while unexposed areas are removed when negative resists are used. To achieve reproducible results, temperatures between 21 and 23 °C ± 0,5 °C for solvent developers (AR 600-50, -50, -56) and ± 0,5 °C
Developer AR 600-50 is a solvent-based developer which was especially designed for copolymer films (AR-P 617). With this developer, the sensitivity of the e-beam resist is further enhanced.
Developer AR 600-55 is also solvent-based, similar to the following AR 600-56 resist. As high speed developer, AR 600-55 is preferably used for PMMA films (AR-P 630-670), if short development times for a high process throughput are desired. Copolymer films (AR-P 617), e.g. also as two layer system PMMA/copolymer, can likewise be developed with this developer.
Developer AR 600-56 is slower than 600-55 and preferably used for PMMA films (AR-P 630-670), if high resolutions and a high contrast are desired despite prolonged development times. This developer is also suitable for copolymer films.
In contrast to novolak-based resists, the development of PMMA layers may be interrupted at any time and continued later without problems. To achieve a particularly high resolution, isopropanol or isopropanol/water developers may be used. In this case however, very high doses are required for exposure.
The aqueous-alkaline developer AR 300-40 product line comprises metal ion free developers of various concentrations. Usage of these developers minimises the possibility of metal ion contamination on the substrate surface. They exhibit excellent netting features and work, as aqueous-based solutions,without leaving any residues. The respective developers are especially adjusted for novolak-based ebeam resists of the AR-P 7000 product line. Especially developer AR 300-46 and 300-47 are recommended (some also in dilutions) for the novolak-based e-beam resists AR-P 7000. →Metal ion free developers are more sensitive to dilution variations. These developers should thus be diluted very carefully, if possible with scales and immediately prior to use in order to assure reproducible results.
Higher developer concentrations of AR 300-40 formally lead to a higher photosensitivity for positive resist developer systems, resulting in a minimum exposure intensity required, reduced development times, and a high process throughput. Possible disadvantages are however a higher dark
Low developer concentrations of AR 300-40 result in a higher contrast for positive resist films and reduce the resist removal in unexposed or only partly exposed areas even at longer development times.
The effectiveness of the developing bath for immersion development is limited by factors such as process throughput and CO2 absorption from air. The throughput is dependent on the fraction of exposed areas. CO2 absorption is also caused by frequent opening of the developer container and results in a reduced development rate.