4. Development

Development

During development, positive resist films are structured by dissolving 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 ± 0.5 °C should be maintained.

All offered developers (AR 300-35, AR 300-26, AR 300-40) are suitable both for immersion and puddle development, while developers AR 300-26 and 300-40 can additionally be used for spray development.

Optimally adapted developers and dilutions for each resist are specified in the product information. Entries like for example AR 300-26 1 : 2 indicate a dilution of 1 part of developer AR 300-26 with 2 parts of DI water.

The optimal development time is dependent on the respective resist type and film thickness as well as on the exposure wavelength, tempering and development procedure. Favourable development times for films of up to 2 μm are e.g. for immersion or puddle development in a range between 20 and 60 s and should not exceed 120 s. Layers of up to 10 μm thickness require 2 to 10 min, while films with thickness values of up to 100 μm may need development times of more than 60 min. The more intensive spray developments require shorter times.

Developer 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 parameters contrast and sensitivity are adjusted via the developer concentration by defined dilution of the developer with DI water.

Note: Metal ion-free developers 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 detail rendition.

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.