The beginning of electron beam lithography dates back to the early 1980s when the first PMMA resists were developed, with chlorobenzene as first solvent. This solvent most efficiently dissolves the various PMMAs (with different molecular masses of 50K to 950K) and thus also allows high solid matter content and the generation of thick films during the coating step. Furthermore, the quality of chlorobenzene PMMA resist coatings is excellent.
With respect to health-related issues, however, chlorobenzene is not the first choice. Evaluating the health-hazardous aspects of solvents, anisole performed significantly better in this respect. Today, PMMA resists are consequently offered worldwide with anisole as solvent. Allresist furthermore provides ethyl lactate-containing resists which are even less harmful. A small disadvantage of ethyl lactate PMMA resists is however the low solubility of the polymers in the solvent, which only allows the manufacture of films with relatively low thicknesses.
The different solvents exhibit no influence on further process parameters of resist films, since the solvent is expelled after the soft bake (150–180°C). PMMA films have identical lithographic properties, even if these films were originally generated with different solvents.
Overview E-beam Other Resists