4. Development

4. development

Development

During development, positive resist films are structured by dissolution of exposed areas, while unexposed areas are removed if negative resists are developed. For reproducible results, temperatures between 21 and 23 °C with a temperature constancy of Δ 1 °C should be maintained for solvent-based developers (AR 600-50, -55, -56), and Δ 0.5°C for aqueous-alkaline developers (AR 300-26, -35, -40). One exception is the CSAR 62, since this resist can also be developed with specific developers at lower temperatures< 0 °C.

The solvent-based developer AR 600-50 was specifically designed for copolymer films (AR-P 617) and enhances the sensitivity of this e-beam resist even further. The developer AR 600-55 is, just like AR 600-56, also solventbased and is preferred as fast developer for PMMA films (e.g. AR-P 630 - 670 series), if short development times are required to achieve e.g. a fast production throughput. Copolymer films (AR-P 617) can also be developed either alone or in a two component system PMMA/copolymer with this developer.

Development AR 600-56 develops more slowly than AR 600-55 and is preferably used if a good resolution and high contrast (with at the same time prolonged development times) is desired for PMMA films (AR-P 630 - 670 series). This developer can also be used for AR-P 617 copolymer films.

The development of PMMA films may, in contrast to novolac-based resists, be interrupted any time and continued later as often as desired. To obtain a particularly high resolution, developers with isopropanol or isopropanol/water should be used. In this case however considerably higher exposure doses are required.

For the development of exposed CSAR resist films, developers AR 600-546, 600-548, and 600 549 are well suited. As weakest developer, AR 600-546 provides a broad process window with the highest contrast values > 15. If the stronger developer AR 600-548 is used, the sensitivity can be increased by a factor of 6 to 10 μC/cm². Developer AR 600-549 with intermediate strength renders CSAR 62 twice as sensitive as compared to AR 600-546, shows likewise no dark erosion, and the contrast is about 4.

The aqueous-alkaline developer series AR 300-40 include metal ion-free developers with different concentrations. The use of these developers reduces the danger of metalcontamination on the substrate surface. All developers have excellent wetting properties and work without leaving any residues. Developments AR 300-46 and 300-47 are specifically recommended for the novolac-based e-beam resists AR-P/N 7400 … 7700 (in dilutions, if required).

Development concentrations as listed in our product information were determined for specific film thickness values or process parameters and can only serve as guideline values under other conditions. The exact developer concentration has always to be adjusted to specific demands (film thickness, development time, tempering). The two parameters contrast and sensitivity are adjusted via the developer concentration by defined dilution of the developer with DI water.

Note: Metal ion-free developers of the 300-40 series are more sensitive to dilution differences than buffered systems. These developers should be diluted immediately prior to use and extremely thoroughly, if possible with scales, in order to assure reproducible results.

Higher developer concentrations formally result in an increased light sensitivity of positive resist developer systems. The required exposure energy is minimised and the development time is reduced, which allows for a high process throughput. Possible disadvantages are an increased dark erosion and (in some cases) a too low process stability (too fast). Negative resists require a higher exposure dose for crosslinking at higher developer concentrations.

Lower developer concentrations provide a higher contrast for positive resist films and reduce resist erosion in unexposed regions or only partly exposed interface areas even at longer development times. This particularly selective working method ensures a high degree of detail rendition at higher exposure intensities.

The effectiveness of the developing bath for immersion development is limited by factors such as process throughput and CO2 absorption from air. The throughput depends on the fraction of exposed areas. CO2 absorption is also caused by frequent opening of the developer bottle and leads to a reduced development rate. This effect is avoided by if the surface of the developer bath is kept under nitrogen.