In the first step of the LIGA process a resist layer is patterned by deep etch X-ray lithography. The exposed parts are dissolved by an organic developer. To achieve perfect microstructures the development must be free of residue, and the unexposed parts should not be attacked. Our studies showed that the solid PMMA material in the resin, as well as the unexposed resist contains at the applied developer temperature soluble parts. Therefore the molecular weight distribution of the resist and the solid PMMA material was investigated as a function of the hardener system respectively the initiator and the regulator concentration. Formation of low molecular weight molecules in the resist layer can only be suppressed if the hardener content is small and if the resin contains no low weight molecules. On the basis of these findings an optimised resist was produced and the quality of the microstructures considerably improved.
