During development, a positive tone resist film is structured by a removal of exposed areas, while unexposed areas are removed if negative resists are used. To achieve reproducible results, temperatures between 21 and 23 °C 0.5 °C are highly recommended.
Allresist offers two different kinds of developers which are either buffered systems (AR 300-26, AR 300-35) or metal ion free (unbuffered) TMAH developers (AR 300-44 … 475):
Developer AR 300-26 is a buffered system with high activity which is preferably used for the development of thick resist films > 5 µm, if high contrast, steep edges, and short development times are desired. Provided as developer concentrate, this developer is diluted with deionised water and can also be used for spray developments.
Developer AR 300-35 is a buffer system with broad process range and particularly characterised by a wide variation range with respect to contrast and sensitivity. This highly versatile developer suitable for most photoresists is provided as developer concentrate which can be diluted with deionised water. The undiluted developer solution is primarily designed for the development of 3 – 6 µm resist films. This developer is suitable for aluminium-containing surfaces, since it does (in contrast to other developers) not attack aluminium.
The developer product line AR 300-40 comprises four metal ion-free developers of various concentrations, which particularly well meet the high demands of micro lithographic applications in semiconductor industry. The use of these developers minimises the possibility of metal ion contamination on the substrate surface. They exhibit excellent netting features and work, as aqueous alkaline solutions, without leaving any residues. The developers are each adjusted to the different resist systems AR-P 3000-5000 and 7000.
Metal ion-free developers are more sensitive to dilution variations than buffer systems. These developers should be diluted very carefully, if possible with scales and immediately prior to use, in order to assure reproducible results.
Higher developer concentrations result in an increased light sensitivity of positive resist developer systems. The required exposure energy is minimised and development time is reduced, allowing a high operational capacity. Possible disadvantages might be a higher dark erosion of unexposed areas and also a low process stability (reaction too fast). Using higher developer concentrations, negative resists require a higher exposure dose for cross-linking.
Lower developer concentrations provide a higher contrast, e.g. of positive resist films, and reduce the resist thickness loss of unexposed or partly exposed border areas even at longer development times. The best contrast values can be obtained with carefully diluted buffered systems (AR 300-26, AR 300-35). In this case, the exposure energy required is mandatorily increased. Negative resists require a lower exposure dose (for cross-linking) at lower developer concentrations. However, the time for complete development is extended. As a rule of thumb for the developer strength: high speed (strong) or high contrast (weak).
The service life 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 bottle and leads to a reduced development rate.
Different methods exist for the development:
Immersion development: The wafer is completely immersed in a bath and move.
Puddle development: A defined amount of the developer is placed on the wafer, the wafer is then gently turned back and forth.
Spray development: The developer is sprayed through nozzles onto the rotating wafer. This development is significantly faster than other methods.
No interruptions should occur during aqueous alkaline development. If wafers are rinsed with water after development and the development is then continued, development rates will increase significantly.